A MANUAL OF THE LATEST APPROVED MATERIAL, INCLUDINGITS USE, OPERATION, INSPECTION, CARE AND MANAGEMENT AND METHOD OF INSTALLATION ON BOARD SHIP
CHAPTER I
INCANDESCENT LAMPS
General Considerations of Naval Types
The incandescent lamp has at least two great advantages over almost all other sources of light: the first is that it can be turned into any position which will best utilize its light; the second is that the distribution of the luminous intensity of the lamp can be varied within wide limits by the mere shaping of its filament. It is an interesting fact that, while much has been done towards improvements in details, the incandescent electric lamp, as invented twenty-five years ago, is still much the same as the original invention in general appearance and construction. The lamp is essentially a filament of carbon heated to incandescence by the passage of an electric current, the filament being enclosed in an exhausted transparent receptacle to prevent that combustion of its material which would immediately ensue if the material were subjected to high temperature in the presence of oxygen; hence oxygen must be rigorously eliminated and this can be accomplished by exhausting the receptacle by some form of air pump and removing residual oxygen by chemical combination.
1 To be continued in succeeding numbers of the PROCEEDINGS and on completion to be published in book form.
The availability of a material for filaments depends upon two qualifications: first, it must be capable of attaining extremely high temperatures without fusing or volatilizing, and upon this qualification depends the efficiency of the material as an illuminant; second, it must be a conductor of electricity.
These two conditions apparently exclude all substances except carbon and the metals with the exception, perhaps, of certain oxides, as a comparison of incandescent lamps, notably those used in the Nernst and Osmium lamps; the oxide types are, however, too fragile for ship use. Practically the conditions narrow the usual selection to carbon, since, as all substances are fused and volatilized at or below the temperature of the electric arc, the arc must represent the best possible source of artificial illumination. The temperature of the incandescent filament is lower than that of the arc and therefore the illumination of the arc must be the superior; still, the temperature of the filament at incandescence is probably as high as 1800° C., a temperature higher than the fusing point of platinum. Carbon, then, not only fulfills the necessary conditions but is at the same time cheap and abundant and possesses the property, unlike metals, of decreasing its resistance with rise of temperature, the resistance of a filament at incandescence being only about half its resistance when cold.
The problem of the filament is to obtain a homogeneous carbon whose specific resistance will be the same in all parts that the filament may not tend to burn away in one section more than in another; and to construct a dense carbon which will not readily disintegrate and blacken with carbon dust the interior surface of the exhausted receptacle, commonly called the bulb; these conditions satisfied, the resistance necessary to the different filaments are readily adjustable by length and cross-sectional area.
The question of selection of a desirable incandescent lamp, apart from those entering into methods of construction, is dependent upon the following considerations:
The Source of Illumination.—This has been determined by experiment to be usually a carbon filament heated to incandescence in an exhausted bulb whose vacuous space is devoid of oxygen.
The Intensity of Illumination.—The number of lumens
Line Drawings
emitted from a source of light are measured by reference to the standard candle and are expressed as so many candle-power for the particular source. Types of incandescent lamps are therefore separated in this consideration by the candle-power emissivity for which they are designed, or "rated." Ordinarily comparisons are made on the 16-candle-power lamp which is regarded as the universal practical standard.
In the navy the following candle-powers are used:
Regular Lamps
16 candle-power.
32 candle-power.
150 candle-power (diving lamp).
5 candle-power (instrument lamp).
Instrument and Special Lamps
10 candle-power (telephotos lamp).
2 candle-power (instrument lamp).
1 candle-power (instrument lamp).
6 candle-power (torpedo lamp).
All of these classes have their bulbs of clear and transparent glass. In the case of the 16-candle-power lamp a frosted type is allowed, which gives a diminished candle-power after frosting, but the light emitted is softer for reading or for desk use. The different types are shown in outline in Fig. 1. The total number of lamps allowed each ship is on the basis of four for each outlet.
The 16-candle-power lamp is the working lamp for general lighting throughout the ship.
The 32-candle-power lamp is allowed for signals, running lights, truck lights, etc., and can be used to advantage to increase the light in dimly-lighted magazines and shell-rooms where the 16 candle-power originally installed is insufficient. The allowance furnished a ship, however, restricts this type of lamp to navigational and signal use.
The 150-candle-power lamp is supplied for diving use.
The 5-candle-power instrument lamp is for illuminating the indications of "lamp indicating instruments," such as the Helm Angle Indicator, Helm Telegraph, Engine Telegraph, and for lighting binnacles and mechanical telegraphs.
The 6-candle-power torpedo lamp is mounted on the end of a rod for examining the interior of automobile torpedoes and is made long and narrow that it may be readily inserted in the small • orifices in the side of the torpedo.
The 10-candle-power telephotos lamp is an especial form of lamp for the telephotos type of (red and white) lantern of the night signalling lanterns. The lanterns of night signalling sets of the General Electric Company's manufacture and some telephotos lanterns are supplied with a single 32-candle-power standard lamp in each half of the lantern; the usual telephotos lantern requires four 10-candle-power lamps in the red half and three in the white half.
The 2-candle-power lamp is for illuminating the dials of the Fiske type of instruments, and the 1-candle-power for the same purpose in the Cory instruments, no greater intensity being necessary in either case. A 10-candle-power regular lamp is sometimes met with but its intended installation in engine- and fire-rooms effects no good economy when compared with the loss of illumination in those locations.
Lamp Voltage.—The voltage which is to be maintained at the terminals of a given lamp is that voltage which will produce the rated candle-power, at the resistance of the filament, and is restricted by the fact that the life of the filament decreases as the standard voltage is increased, that is, a lower voltage lamp will usually be the longer lived.
The voltage of lamps, except the 1 candle-power (which has an especial voltage of 10 volts for convenience of construction), primarily depends upon the terminal voltage of the dynamos which are to supply the energy. Formerly dynamos have been prescribed for a terminal voltage of 80 volts and the voltage of lamps has been prescribed at 80 volts, mean, between the limits of 78 volts and 82 volts; the variation in limits being allowed in order that a larger number of lamps may be obtained from any manufactured lot than would be practicable if the normal (80 volts) was rigidly prescribed and fixed.
Upon the adoption of the 125-volt dynamos, and for use with the 110-volt machines installed in auxiliaries, both 123-volt and 110-volt lamps have come into use, the 123-volt being now the standard for 125-volt installations. In order to obtain a range of selection, variations in limits are also prescribed for the 123-volt and 110-volt lamps as in the case of those for 80 volts.
A condition which affects the selection of voltage is the question of commercial supply and demand, that is, the ability of the manufacturers to fill an order in view of other contracts. For a 125-volt installation a lamp of any voltage between 110 and 124 volts may be used; all types are commonly used by commercial companies at different distances from the power-house to accommodate the lamp to the loss of potential due to distance, or for saving in cost of copper by reason of available reduction in wire size.
The average ratio of supply to demand for Ho-volt lamps in the market is as 6 to 9; lamps at this voltage are therefore difficult to obtain, and the case is approximately the same for other voltages up to 119 volts. It is not advantageous, considering the short distances of runs in ships, to endeavor to reduce wire size by using a variety of voltages, and an allowance of 3 per cent drop renders a 123-volt lamp available at all ship distances and necessitates but one type. In the variations of a supply furnished a ship, occasioned by the limits in acceptance, those lamps having voltages lower than 123 are placed at the farther end of lines of wiring, and those nearer to or above 123 volts, in the vicinity of the dynamo-rooms.
Lamp Efficiency.—The economic performance of a lamp is measured by the number of units of energy which the lamp consumes, and this energy is electrically measured by the number of watts required by the lamp, as determined by the product of the current passing through the filament and the voltage at its terminals; this product is called the total watts. The total watts divided by the candle-power of the lamp, or the number of watts per candle-power (w. p. c.), is taken as the measure of the lamp's efficiency.
Experiment has determined three practicable efficiencies: 3.1, 3.5, and 4.0 w. p. c. As explained under the subject of voltage, to obtain a range in selection, these efficiencies are prescribed between limits: 2.9 to 3.3 w. p. c., 3.3 to 3.7 w. p. c., and 3.6 to 4.0 w. p. c.
A " high " efficiency of 3.1 w. p. c. will consume the least electric energy for a given lamp of given candle-power, and will give the most brilliant light as compared with lamps of the same candle-power at lower efficiencies, that is, the light will be whitest. The condition obtains only because the lamp at 3.1 w. p. c. is at the highest temperature. In reality no lamp can be said to be of or have a greater or less efficiency than another: one lamp may be burned, or "run," at a greater efficiency, but it possesses no greater efficiency in itself for the reason that any other lamp can be run at an efficiency just as great; and, further, any lamp can be run at any desired efficiency, approaching in its intensity the electric arc, dependent only upon the temperature, the limiting efficiency being that necessary to the instantaneous destruction of the filament.
Hence, a higher efficiency means a higher state of temperature of the filament; it also means that the filament will burn out more quickly and have a short life. The filament of lamps at an efficiency of 3.1 w. p. c. have the comparatively short life of about 400 hours, and are desirable for those uses alone where extended life is not a consideration as compared with brilliancy, or where a brilliant light is required for but a short time, or intermittently, as in the case of the 150 c. p. diving lamp.
As a life of 1000 hours and above is usually desired and expected, a low efficiency is prescribed for general use; that of the 80-volt lamps heretofore in use is 3.6 to 4 w. p. c., giving long service but showing a yellowish light as compared with the commercial lamp of 3.5 w. p. c. The present standard efficiency is 3.5 w. p. c., between the limits of 3.3 and 3.7 w. p. c., and applies to all classes of lamps except the 150 c. p. diving lamp, whose efficiency is 3.1 w. p. c.
The shorter life of a lamp at high efficiency is taken advantage of in testing the life of lamps from the great saving of time. Though a lamp be designed for an efficiency of 3.5 or 3.8 it can be made to burn at any other efficiency by merely altering the voltage, but it will give a different candle-power from that of the design; for example, a lamp which is producing 16 candle-power at 80 volts is under life test and it is desired to burn it at 3.1 W. p. c. instead of at the 3.5 of the design; it is only necessary to raise the voltage at the lamp terminals to 82.4 volts, and the efficiency will be 3.1; but the lamp will produce nineteen candlepower at the new voltage instead of sixteen, and will consume more electrical energy than if burned at 3.5 w. p. c.
In addition to changing the efficiency and farther decrease the time necessary for the life test, it is the custom to burn the test lamp only during its "useful life," or that number of hours in which its candle-power shall have been decreased to 80 per cent of the rated candle-power.
[Note 1.—The high efficiency of the Nernst lamp in particular has of late turned the attention of lamp manufacturers to metal filaments, from which high efficiencies and consequent economy in energy, are readily derivable; the life of the lamp is about 800 hours. One type has a filament made from the metal tantalum which is, however, brittle and has not met with success in alternating current work; the latest development is a tungsten filament, giving the high efficiency of 1.0 w. p. c.; the saving of energy, economy, of this type of filament over the usual carbon filament type is therefore 71 per cent. The type has not as yet been extensively introduced, and it will probably be many years before the carbon filament lamp is importantly supplanted.]
The Type of Bulb.—The type of bulb is a question of dimension for filament area and for the intended use; the commercial "straight side," or "parachute " bulb is the approved standard.
The Type of Base.—The Edison screw base is in such general use and is so well adapted for securely holding a lamp in place that it has been the permanent standard.
Lamp Manufacture
The Filament.—The original compound is a pyroxylin made from cotton. The steps of reduction to cellulose vary with different manufacturers, but the main reactions are as follows: The pyroxylin is dissolved by hot concentrated 40 per cent zinc chloride forming a syrupy mixture from which a hydrated cellulose zinc-oxide is precipitated by alcohol. The zinc is freed by hydrochloric acid and washing. The pyroxylin is reduced to cellulose by ammonium sulphide. The resulting compound is a heavy, brownish or amber-colored liquid known as “tamadine," and of the consistency of heavy molasses.
The liquid is put in an inverted bottomless jar, over which is fitted a cap for application of a light air pressure; the neck of the jar is fitted with a pipette nozzle, the diameter varying for the diameter of the filament to be produced. The liquid oozing through the nozzle passes in a thread to a “tub“placed in a slowly-revolving jar which is filled with alcohol to harden it. The tubs undergo several washings to remove the adhering zinc chloride; acidulated washes are sometimes used to remove any stickiness of the surface. In this state the thread becomes a milky-white cord resembling, and a little thicker than, boiled vermicelli.
The cord is thoroughly dried on the surface of a slowly-revolving drum, which is heated internally by gas or steam; drying to a tough, flexible, lustrous thread resembling a white horse hair. In this state it is wound about the posts of a former, or mandrel, having a large and small post; turns are taken around the larger post before crossing to the other in accordance with the number of turns, or spirals, desired in the finished filament. The spirals on the mandrels are slightly baked in an oven to ensure temporary retention of form, and are then cut at the smaller post and taken off the mandrel.
Fig. 2. – Bottle for flashing or treating.
The filaments are then packed in metal boxes filled with peat and brought to a red heat in an oven; this process gives all the shrinkage that will result in carbonizing; at this stage the filament is not yet a conductor of electricity.
The filaments, now of a black color, are packed with a refractory material in plumbago crucibles and carbonized, retaining the formed shape permanently; they are separated carefully and the ends trimmed to the finished length.
The manufacture of the filament thus far assures neither homogeneity throughout nor the appropriate resistance; both are accomplished by the following ingenious process, known as " treating " or " flashing " :
The filament is connected by clips (A, Fig. 2) in the air-tight cork of a bottle B, which contains a volatile hydrocarbon such as gasoline, benzine, etc. The clips are metallically connected with the binding posts, C, to which wires from a source of electricity at proper voltage are connected through a clutched switch and an ammeter (not shown). When the switch is closed the terminals, C, are at a slightly higher potential difference than that at which the lamp is to be used. The bottle is first exhausted, the switch is closed, and the filament (within the bottle) becomes incandescent. The heat decomposes the vapor emitted by the hydrocarbon and deposits carbon on the filament; those sections of the filament which have the greatest resistance (or which are of least diameter) will heat most and receive the greatest deposit of carbon, and proportionately for differences in diameter; the whole filament thus becomes homogeneous and uniform in resistance throughout, no section tending to heat more than another.
As the carbon is deposited the resistance decreases and the current increases. The pointer of the ammeter moves along the scale to an indication where the desired resistance, and consequently current, has been reached; at this point the pointer closes a circuit which automatically shunts in a current from another circuit and which in turn throws out the switch clutch; the switch springs open and cuts off the current from the filament, stopping any farther deposition of carbon.
It is optional whether the filament be suspended in the vapor above the liquid in the bottle or be submerged; results of test show that filaments flashed in the vapor are less likely to cause blackening of the bulb than when treated by submerging. The latter process is sometimes used because it is the cheaper and is also the safer from explosions occasioned by access of air.
In making the filament the length and cross-sectional area are the considerations sought in homogeneous material in determining the resistance for a required candle-power at the voltage at which the lamp is to be burned.
Filaments of the 150 c. p. diving lamp are made either of tamadine or carbonized split bamboo, but neither style of filament have as yet proved successful in this type of lamp.
Tamadine filaments are usually known to the trade as “squirted " filaments.
Figs. 3 and 4 show the different types of filaments of naval incandescent lamps. The spiral type (C, Fig. 3) was used in 80-volt lamps of 16 and 32 c. p., having the old cruiser type of bulb, now obsolete. The oval type (E, Fig. 4) is used in those having the present parachute standard bulb for the 16 and 32 C. p., and in the 10-candle-power telephotos lamp. The practical difference between the oval and spiral filaments is that the oval is anchored while the spiral is not.
Fig. 4 – Stages of lamp assembly
The filament of the 15o c. p. diving lamp is made in a two-coil spiral (D, Fig. 3) for the 8o-volt type; that for the 123- and 110 volt types is a double loop, or double "horse shoe" (B, Fig. 3), the loops being set at right angles and in series with each other.
The filament of the 5 c. p. is a two-coil spiral (D, Fig. 3). That of the 2 c. p. is a double loop for the 80-volt type and a three-coil spiral (E, Fig. 3) for the 123-and 110-volt types. The filament of the i c. p. lamp is a single loop (A, Fig. 3), as is also that of the 6 c. p. torpedo lamp; the long filament of the 6 c. p. is ordinarily anchored to the tip of the bulb instead of to the flyer to obtain better centering and steadiness.
The Flyer.—Two 3-inch copper leading wires are first attached to two platinum wires, each about ½ inch in length (A, Fig. 4) ; the copper wire is heated in a blow lamp and the platinum wire forced into the fused end of the copper, making a secure joint. Notwithstanding the comparatively great expense entailed by the use of platinum for these lamp ends (which are to be fused into the glass of the flyer) no other metal so well serves the purpose: first, because platinum will not oxidize at the high temperature necessary for fusing the glass, hence the joint will be tight and not cause a leakage of air into the vacuous space; second, as the coefficients of expansion of glass and platinum are practically the same, the expansion of the metal is not likely to crack the glass of the flyer and admit air.
The combination of the copper and platinum leading wire is next assembled in a glass tube haying a bell-shaped mouth (C, Fig. 4), the platinum wire being fused in the glass. The finished flyer is shown at D. The wire shown in the center of the flyer is of metal, usually copper, and is called an anchor; its office is to secure the bottom of the filament spiral, thus centering the filament, steadying it against vibration, and preventing it from swinging against the glass of the bulb; it requires but a light touch of the incandescent filament to fuse the glass, collapse the bulb at the point of fusing, admit air, and destroy the filament.
The filament ends (B, Fig. 4) are next attached to the platinum wires of the flyer, and the spiral to the anchor, by a non-fusible cement, or carbon paste, called a "clamp"; the date of manufacture is written in ink on the surface of the glass of the flyer, and the combination of this stage (E, Fig. 4) is ready for inserting in the bulb.
The length of the flyer for the 80-volt, 110-volt, and 123-volt types is not the same, due to the difference in length of the filament.
The Bulb.—The construction of the bulb is purely a glass manipulation. F, Fig. 4, shows the bulb as received from the glass factory; G, at the stage at which the flyer is fused in.
The assembly of the bulb and flyer consists in carefully inserting the combination shown at E, Fig. 4, into the bulb, G, and fusing the edges of the bell mouth of the flyer to the edge of the bulb; the finished product is shown at H, in which stage the lamp is ready for exhausting.
Commercially standard bulbs are generally denoted by a number which represents their diameter in eighths of an inch; thus a 2 5/8 -inch bulb is designated as No. 21.
Forming of the Vacuum.—Upon the best performance of this office depends that vital consideration, the life of the filament, and consequently the life of the lamp; the rationale of the method is the elimination of oxygen.
The narrow tube which is shown attached to the top of the bulb, H, Fig. 4, is coated internally with a red chemical compound, a trade secret, but containing red phosphorous which takes up the residual oxygen in the bulb when heated forming a transparent phosphoric acid gas. The end of the narrow tube is next inserted in the air-tight rubber bushing of a tube connected with a mechanical, Sprengel, or Weston, type of air pump and exhausted until the attached column of mercury shows about 30 inches. The copper leading wires of the lamp are now attached to clips on two wires which are fed at the potential at which the lamp is to be run and the current is turned on. The color of the bulb will now be a pale blue.
A blow-pipe flame is applied gently to the narrow tube until the red chemical volatilizes and disappears and the lamp shows a clear or bright yellow; the narrow tube is then gently seared over ("sealed") next the bulb and twisted off, leaving the little nipple generally seen on incandescent lamps. I, Fig. 4, shows the lamp at this stage.
The bulbs are now tested for vacuum by brushing the leading wires against a plate attached to one electrode of a Ruhmkorff coil, the lamp being held in the hand. The sufficiency of the vacuum is judged by the color and the appearance of the light inside. The bulb is then ready for the base.
Attaching the Base.—The Edison base consists of a threaded spun brass open-ended cylinder, perforated with one hole near the middle of its length, and a brass disc perforated through its center. The method of attaching the base, using plaster of paris only, is as follows:
The combination (I, Fig. 4) is put in a frame moving perpendicularly, the cylinder is centered under the frame and the disc is entered at the bottom of the cylinder. The copper leading wires are threaded; one through the perforation of the cylinder, the other through the center of the disc, and the cylinder is filled with plaster of paris.
The frame is now pushed down and the wires drawn through. As soon as the plaster hardens the overflow is trimmed off, the leading wires are cut close to the cylinder and disc and soldered. The bottom of the base is then coated with shellac and the lamp is finished. This method, though common, has the serious objection that, notwithstanding the protection afforded, the shellac proves unequal to keeping out moisture when the lamps are stored in such moist locations as ship store-rooms; the plaster of paris being hygroscopic, sufficient moisture is taken up to cause a short circuit between the copper leading in wires in the lamp base which cannot be readily removed by drying.
A second method considerably in vogue is to crimp the bottom of the cylinder and cement in a treated porcelain plug or button in which the brass disc is imbedded; the bulb is secured to the cylinder by moisture proof cement. The porcelain plug has channels for the leading wires to the disc, and to the side of the cylinder, or to a bottom edge if so connected. It is important that the porcelain insulate between the leading wires. The channels should be carefully filled with some .water repellent substance. The method has the same objections cited for plaster of paris, but in a lesser degree.
The latest method, in which a glass plug is used instead of porcelain, is an improvement on the last. The plug is made by forming melted glass in the crimp of the base, the contact piece being secured by rivet attachment. In this method but one channel is necessary, the other leading in wire being soldered at the top of base.
The bases of the 150, 32, 16, and 10 c. p. lamps are required to be of standard form of Edison base. The base of the 5 C. p. is of the candelabra form of Edison base. The bases of the 2 C. p. and 2 c. p. are of the minature form of Edison base.
Test of Voltage.—The lamps are next "run through" a photometer to measure the voltage at which the rated candlepower is maintained, the screen being moved along a scale marked in volts, the lamp rotating at 180 revolutions per minute. All that is sought in the commercial test is to ascertain what voltage the particular lamp requires for the rated candle-power; this complying with specifications, the watts per candle-power and actual candle-power are taken as correct. Lamps have heretofore been marked for the rated candle-power and rated (not actual) voltage; a mark showing the actual voltage to the nearest volt is now shown on the label.
Life Test.—A number are selected and started on a life test (useful life being tested) for loss of candle-power in the interval.
Frosting.—The bulbs of those lamps which are to be frosted are, after being tested for voltage, submerged in a solution of hydrofluoric acid and ammonium chloride; the operation requires but a fraction of a minute.
Inspection and Test of Incandescent Lamps.1
In order that there may be no misunderstanding as to what will be expected of a delivery of incandescent electric lamps the inspection and tests which the lamps will be subjected to are prescribed in the specifications substantially as follows:
All lamps are to conform in their general shape and form to the official drawing, from which Fig. I is taken.
The overall dimensions of the standard 32, 16, and 5 c. p. lamps must not exceed the dimensions in inches in the following table, in order that they may fit in the standard types of fixtures:
TABLE I
32 c.p. 16 c.p. 5 c.p.
Length overall 4 7/8 4 7/8 2 7/8
Length of bulb without tip 3 11/16 3 11/16 2
Maximum diameter of bulb 2 5/8 2 ½ 1 3/8
The overall dimensions of the iso c. p. (diving), Jo c. p. (telephotos), and 2 c. p. and i c. p. (instrument), and 6 c. p.
2 All inspections and tests herein explained are those in current practice in the Equipment Department of the New York Navy Yard. For the sake of brevity, it may be here stated that in addition to items of specification (which are alone taken up in the descriptions following), the blank forms used by that department, largely inaugurated in the department itself, are made complete as to details and features of the article under inspection, the marks of manufacturers, workmanship, accessories, dimensions—in short, any detail for recognition, future requisition, or Incidental and necessary to repair. A photograph of a new article is always taken in three views, and often the whole is disassembled and all parts photographed.
(torpedo) lamps must conform to the dimensions shown in the official drawing.
The lamps must be made of the very best materials, and must be of the best quality and finish and uniform in size.
The filaments must be centered in the bulb and, in the case of the 32 c. p. and 16 c. p. lamps, must be anchored. They must not droop appreciably during the life of the lamp ‘when the lamp is run in a horizontal position.
Each lamp must have its rated candle-power and the voltage (to the nearest volt) necessary to give this candle-power, and the name or trade-mark of the maker shown on a printed label or otherwise clearly or indelibly marked on the bulb.
The lamps must be so designed that when burned at the rated mean horizontal candle-power the volts and total watts will not fall outside of the limits prescribed by the table on opposite page.
Measurements for mean horizontal candle-power are to be made by revolving the lamps at about, and not less than, 180 r. p. m. with the axis of the lamp vertical. When making this determination the lamps shall be so placed in the photometer that the horizontal line through the center of the screen will cut the lamp at its maximum diameter.
From each barrel or lot of 200 lamps there will be selected at random 10 lamps for the purpose of determining the initial voltage, and the total watts at the rated candle-power, and the physical characteristics of the lamps. These lamps will be known as test lamps. If the voltage or total watts of any two of the test lamps from any barrel or lot of zoo lamps is found to fall beyond the limits allowed in Table 2, above, 10 more lamps will be selected at random from the same barrel or lot, and if any one of these additional lamps is found to fall beyond the allowed limits of voltage and total watts, the entire barrel or lot will be rejected without further test. If the voltage or total watts of more than two of any lot of 10 test lamps falls beyond the allowed limits, the barrel or lot from which these lamps were selected will be rejected without further test. If any one of the 10 test lamps selected from any barrel or lot of 200 lamps shows a poor vacuum. a loose base, a spotted or discolored filament, or any other physical defect incompatible with good workmanship, good service, or with any clause of these specifications, 50 lamps will be selected from this barrel or lot, and should 10 per cent of these 50 lamps
TABLE No. 2.
be found to have any of the physical defects above mentioned, the entire lot from which these lamps were selected will be rejected without further test.
From the 10 test lamps selected from each barrel or lot of 200 lamps passing the above tests for voltage, total watts, and physical characteristics, one lamp shall be selected and shall be known as a life lamp. This lamp shall be the one from each lot of 10 test lamps which measures closest to the mean of the limits for volts and total watts as given in columns 5 and 6 of Table 2, above. From the life lamps so selected a given number will be tested for candle-hour performance, and this test will be known as the life test. The number of lamps that will be put on life test will depend upon the number of lamps delivered.
When lamps are purchased in lots of 2000 or less, 10 lamps will be selected for life test; in lots of from 2000 to 5000, 20 lamps will be selected; in lots of from 5000 to 10,000, 30 lamps will be selected; in lots of from 10,000 to 30,000, 50 lamps will be selected for life test. The lamps selected for life test will be brought to that value at which the lamp burns at 3.1 watts per mean horizontal candle-power. Throughout the life test each lamp will be burned at the particular voltage which was required to give 3.1 w. p. c. initially. The average value of the candle-hour performance of the lamps subjected to life test shall not be less than the amount in column 8, Table 2, above.
The candle-hour performance of a lamp will be calculated, as described below, from the observed values of the mean horizontal candle-power measured at the beginning of the life test, and at intervals thereafter of 25 hours during the first 100 hours, and thereafter at intervals of not more than 100 hours until the lamps shall have burned out, or fallen to 80 per cent of its test candlepower. In case a lamp burns out, its candle-power at the time of the burn-out will be assumed equal to the last observed candlepower. The candle hours given by a lamp during any one of the intervals of 100 hours or less, as above, will be considered to be the product of the hours denoting the duration of that interval, and the arithmetical mean of the observed values of the mean horizontal candle-power measured at the beginning and at the end of such interval; provided, that if any observed value of the mean horizontal candle-power exceeds the test candle-power by more than 3 per cent, such candle-power shall, in computing the candle hours, be given a value of 3 per cent greater than the test candle-power. The candle-hour performance of the lamps will be considered as the sum of the candle hours given during each of the observed intervals, and up to that time when the lamp shall have burned out or shall have fallen to 80 per cent of its test candle-power.
Test for vacuum will be made with an induction coil previously set for a 3/8-inch spark for regular lamps, and suitably reduced for small lamps having delicate filaments.
The standards of candle-power which will be used in making the above-described tests will be those held in the Equipment Department at the Navy Yard, New York. Any person having a contract for lamps may send to the Equipment Department, Navy Yard, New York, a set of 10 seasoned lamps to be standardized, one-half of which will be returned, and the other half retained for future reference.
All lamps whose bulbs shall burst, or whose • filaments shall break under test or in transit will be rejected from the delivery, and must be replaced at the expense of the contractor. In order to avoid duplication of the life test, no test will be made on any class of lamps until the entire number of such lamps on any contract is delivered, unless it is specified in the contract that partial deliveries are to be made at stated times. In case partial deliveries are required, the entire quantity of each class of lamp constituting the partial delivery must be received before any tests will be undertaken.
Mechanical Construction.—The maximum diameter of the bulb is tested by means of a gauge ring which has an inside diameter equal to the greatest allowed diameter of the lamp, as per table; the lamp must pass through this ring without effort. Two or three other diameters of the bulb and the diameter of the base are calipered. Lengths are measured for correspondence with the prescriptions of the standard drawing. These dimensions are important, to insure fit in standard fixtures.
Examination is made of the following:
That the threads of the base are of the prescribed number and pitch, in order to insure a fit in the standard socket.
That the bulb is securely cemented to the base, and that the cement is moisture proof; tested by placing the lamp under water for an hour or two and wrenching the base.
That the button is so placed that it will insure insulation between the contacts and that the channels are fitted with a water-repellent substance. After the soaking test the lamp is placed in a socket; if short-circuited it will not burn or will burn faintly.
That the leading-in wires are securely soldered to the bottom contact and to the side cylinder; and that they are of copper and have platinum ends in the fused part of the flyer.
That the filament is .centered in the bulb and, if anchored, that the anchor is of metal and is securely fused into the flyer.
That the quality and finish is of the best, judgment being rendered by comparison with a standard sample.
That the lamp is properly labeled for its rated candle-power and the actual voltage, to the nearest volt, which is required to give that candle-power.
That the filament is securely fastened to the leading-in wires and to the anchor. Usually this determination is not definitely demonstrated by examination; as a rule the performance of the lamp on life test will show it, as the filament is likely to separate from the platinum wire if the clamp is poor.
The date of manufacture must be noted, and if not within three months of the date of delivery examination of records is made to insure that the lamp is not of a lot that has been previously tested and rejected.
Photometer Test —In ordinary photometer tests the problem is to ascertain the unknown candle-power of a source of light by comparison with a standard flame or candle, and, incidentally, the rate of consumption of the material which maintains the source. In photometric measurements of incandescent lamps the problem is to ascertain the consumption of electric energy in a lamp of designed, or rated, candle-power by measuring its voltage and current when burning at that candle-power; the product of these two measurements gives the total watts consumed, from which the efficiency can be calculated by dividing by the candlepower.
The photometer used is shown in Fig. 5; it was constructed at the navy yard.
The bed of the photometer, A, is a steel I-beam mounted on heavy cast-iron standards. It carries a steel scale, divided, first, to read directly in candle-power; second, in tenths of an inch over a length of 60 inches, the total distance between sockets for the standard lamp and the lamp under test.
The photometer carriage, B, runs on ways provided on the upper side of the photometer bed, and carries the photometer screen, C (the Lumner-Brodhun is shown, the ordinary Bunsen screen is shown detached at D). The screen has an index line
Photograph
Fig. 5 – Photometer, New York Navy Yard
giving its exact center with reference to the photometer scale; a pin fixes the screen at the 16 c. p. and 32 c. p. divisions, on its rear side is a clamp for holding at any position. For taking readings on lamps of unknown candle-power (when the carriage is to be varied in position) an instrument lamp is provided which illuminates minates the photometer scale at the index line; this is lighted by pressing a button, also on the carriage.
At the right-hand end of the photometer is the socket, K, for the standard lamp, which can be turned about its vertical axis to any angle, as indicated by a graduated circle, and clamped fast in the position by a set screw. An adjustment for height (by collar and set screw) is also provided; when correctly set, the center of the loop in the lamp filament will correspond with the center of the photometer screen.
The rotator, E, for the lamp under test, L, is at the left-hand end of the bed. This consists of a socket rotated at a constant speed of 180 r. p. m. by a direct-connected, 1/6, h. p., motor; electrical connection is made to the lamp by means of two mercury cups. The speed of the motor is regulated by a rheostat of the Carpenter type, P. The motor is stopped and started while the lamp is being replaced by a switch operated by the laboratorian's foot. A snap switch is provided in the rotator circuit.
The rheostat, F, regulates the voltage of the standard lamp; it is wound with No. 22 German silver wire, total resistance 69.5 ohms. The insulated resistance wire is spooled over a brass tube and a section of the surface is bared for contact with sliders, S. in series with the rheostat and the standard lamp. When the sliders have been advanced to the “all-out” positions on the rheostat resistance, there will still be a resistance of 1.5 ohms in circuit due to the rheostat.
The rheostat is so located as to be conveniently in reach of that observer who is reading the voltmeter, G, which is connected across the standard lamp, and the voltmeter, H, and ammeter, J, connected for reading the voltage and current of the test lamp.
The rheostat, R, similar in construction to F, is in the circuit of the lamp under test, and is placed on the photometer bed so that the observer at the screen can adjust the voltage of the test lamp to that necessary for obtaining the proper intensity of light on the test lamp side of the screen. Three coils are shown in the rheostat, of which the smaller is for fine adjustment of the voltage.
When the intensity of the light on both sides of the screen is equal (or “balance" has been obtained) the voltmeter, H, will indicate the voltage of the test lamp for balance. The rheostat, N, is used as a shunt for tests of the 150 c. p. lamp, whose current, 6.25 amperes, would be likely to burn out the rheostat, R, if N were not paralleled across the circuit.
The voltage of the standard lamps varies from 48 to 50 volts, but the rheostat, F, contains enough resistance to cut down the line voltage to the proper value for these lamps when 125-volt lamps are under test.
The rheostat, R, controlling the lamp under test is wound with No. 18 German silver wire; total resistance, 54.7 ohms.
Resistance of top coil 24.7 ohms.
Resistance of 2d coil 7. ohms.
Resistance of bottom coil 23. ohms.
Reading lamps are placed over the instruments and are so shaded that light is thrown on the instrument scales only. These are instrument lamps of 2 c. p. at 80 volts, a 32 c. p. lamp being placed in series to cut down the voltage from the 110 volts necessary for the motor.
The Bunsen Screen.—A spot of grease on a sheet of white paper is placed normal to the optical axis of the photometer; the spot disappears when the paper is equally illuminated on both sides. The spot is central and the field is viewed by 45-degree mirrors set on each side of the screen.
The paper used is Whatman's I A H double elephant; the grease spots are prepared by dipping a warmed disc of brass, about 5/8 -inch diameter, into a paraffin bath; this, after dripping a little, is pressed on a large sheet of paper in a number of places and the excess paraffin removed from the spots by the aid of a sheet of blotting paper pressed by a moderately hot flat-iron. The best spot is then chosen.
The photometer should readily show a difference of 2/10 volt in a 3.6-watt, 80-volt, 16 c. p. lamp with the Bunsen screen, one lamp revolving. With the Lumner-Brodhun screen and stationary lamps, as in checking standards, observations by two persons should check within 1/10 volt.
The Lumner-Brodhun Screen is shown in diagram in Fig. 6 It consists of a gypsum, or MgO screen, held normal to the Optical axis, each face of which is illuminated by one of the lamps under comparison. Two prisms are provided, one of the hypothenusal sides being so recessed and held as to be in contact only at a portion of the length, as shown. The eye at the reading telescope sees a uniformly illuminated field when the faces of the screen are equally illuminated. One face of the screen is seen by reflected light, the other by the light transmitted through the prisms; this is reversed by turning the box through 180 degrees, the surface seen in the first position by reflection being seen by transmitted light in the second.
The trapezoidal-shaped figures of the sight field are illuminated by light from the regions marked 4 and 5 only; the light of the regions 2 and 7 does not pass to the eye piece at all and the field, as distinct from the trapezoidal figure, is illuminated from the test lamp source by the rays 6 and 8 and from the standard lamp by the rays 1 and 3. Hence, there will be contrast between the figure illuminated by 4 and the field illuminated by 1 and 3 on each side of it, and similarly there will be contrast between the figure illuminated by 5 and the adjacent field illuminated by 6 and 8 but in the opposite sense to the contrast for the figure illuminated by 4. There will also be a contrast at the medial line of the sight field between the spaces illuminated by 3 and 6. These three contrasts in different positions enable the operator to check his balance quite accurately, and more so than is practicable with the Bunsen screen.
The Lumner-Brodhun screen can also be fitted with absorption strips (as shown in the path of the rays 1, 3, 6, and 8), interposed in the path of the light from both of the sources; their use is unnecessary when the lights from the two sources are of the same color, and are used only when the lights from the two sources are of different colors.
The rays 1 and 3 from the standard source, and 6 and 8 from the test source, pass through the absorption strips to illuminate the fields but do not illuminate the trapezoidal figures, the figures being illuminated by the active light from each source. There are, therefore, two methods of comparison; by contrast of the active lights from the sources, and by contrast of those active lights as affected by absorption, the comparison being made by contrasting the illumination of the trapezoidal figure with the field immediately adjacent to it. There is also the difference in illumination across the medial line of the sight field, or three ways can be utilized as before but, due to the absorption strips, the contrast between the trapezoidal figures and the adjacent fields will be intensified.
In testing, a Tertiary standard lamp is placed in the socket at K (Fig. 5), and used as a standard for the lamps to be tested; it
Diagram (page 25)
is fixed by the circular scale so that the plane through its filament will be 60 degrees from that of the optical axis of the photometer. Its voltage, as determined in standardization and as recorded by the voltmeter, G, is kept constant for any fluctuation of the line voltage by the rheostat, F. The lamps under test are mounted consecutively in the socket, L, which is kept revolving at 180 r. p. m. by the motor, E, and the voltage of the test lamp is varied by the rheostat, R, until equal balance is shown on the screen, when the voltage as indicated by the voltmeter, H, and the current, as indicated by the ammeter, J, are read. To avoid cracking or scratching the bulbs by contact, which weakens the vacuum, all lamps are handled in the racks only after unpacking.
The number of lamps tested is governed by the specifications above cited.
In order that a representative lot of lamps be tested, the lamps tested are selected equally from all the barrels or packages in the shipment, except in case one or more barrels or packages contain lamps of mixed voltages: in that case the test lamps are so selected that the percentage of each voltage is the same percentage as the number tested is of the number represented by the test, care being taken that some lamps are selected from each barrel or package.
Each lamp is marked in ink on its label with a serial number. This identifies the lamp during the test and upon the records. Failures are recorded by a check mark in the proper column of the test record form opposite the test number of the lamp failing. The mercury contacts on the rotating socket should be clean, well amalgamated, and have sufficient mercury in the cups to insure good contact. The rotating socket should be tried to see that it can be driven at 180 r. p. m. and that it will maintain that speed.
Care should be taken that all working parts of the Bunsen screen are clean and that the two sides are in exactly the same condition. Only a soft chamois cloth is used for cleaning the working parts and a soft camel's hair brush for dusting the screen. These directions apply to the care of the Lumner-Brodhun screen also. When either screen is perfectly clean the direct and reversed readings will be exactly the same. Great care must be exercised in cleaning the Lumner-Brodhun screen to avoid injury to any of the delicate parts.
Before starting to test a voltmeter is checked daily with the laboratory standard voltmeter at the voltages at which it is to be used, and the photometer voltmeters calibrated to conform to it. These photometer voltmeters must be adjusted every time a voltage differing a few volts from that last used is to be read on them. Adjusting by means of a magnetic shunt obviates the necessity of correcting each reading as it is taken.
The ammeter which is to be used is calibrated daily by checking it with the laboratory standard ammeter.
Care should always be taken that no lamp is subjected to a voltage higher than its rated voltage. To accomplish this always have both photometer rheostats "all in" before starting a test.
In standardizing, since the laboratory tertiary standards are 16 c. p., for a lamp of any other candle-power the screen would be placed at that distance on the bar scale from the standard lamp which would accord with the law that the intensity of light varies inversely as the square of the distance; in standardizing a 5 c. p. lamp the screen would, therefore, be set at 6.4 inches on the scale bar from the lesser candle-power, or 53.6 inches from the standard 16 candle-power. The positions for the different types of lamps are, however, marked on the photometer bed, A.
There are two considerations of the foregoing test which deserve some passing explanation; they are the mean horizontal candle-power and the standardization. The first question is what is to be the relation of the filament of the test lamp to the optical axis of the photometer when the lamp is emitting its mean available candle-power. It is not a question as to the standard lamp because that lamp is standardized for the fixed 60-degree position and should obviously be so set.
Two candle-powers are recognized in lamp tests, one given out at the end of the filament, or end candle-power, the other given out at the side of the length of the filament, or horizontal candlepower. A lamp constructed with a filament running straight through would evidently have no end candle-power at all, and, in general, the end candle-power will be less than the horizontal for any type of filament. This suggests that a lamp be so installed in the ship as to emit its light at the side rather than at the end and that, for overhead lighting, the lamp should be laid flat if the side illumination is to be lost in the particular location.
Whether the test lamp shall be set with its axis in continuation of the optical axis of the photometer, end on, or with its axis in, but perpendicular to, that optical axis, has been a mooted point; it is now the recognized practice to adopt the latter method as a better comparison with the usual and necessary practice as to gas flames, etc., and the horizontal candle-power method is very generally accepted.
The method of test of candle-power by fixing the plane of the filament at the best angle for the determination of a good mean is found not to be as fair to the lamp as the determination by rotating at a necessary speed, as the mean horizontal candle-power determined by the latter method is in excess of that for which a comparable mean could be measured for the same lamp when in the fixed position.
Another method of testing, by mean spherical candle-power, deserves no particular mention as it is practically the same in result as the mean horizontal.
The second question, standardization, is dependent upon the reliability of the official reference standards. The Equipment Department of the Navy Yard, New York, is in possession of 18 of the very best standard 16 c. p. lamps extant. These lamps were carefully constructed by the General Electric Company for the especial purpose and were selected as the best of the number of well-seasoned lamps so constructed. They have a loop (horseshoe) filament and operate at between 48 and 50 volts, taking from 1.18 to 1.2 amperes to produce 16 c. p. when at the 6odegree angle. The lamps were standardized by the Physikalish Technische Reichsanstalt, of Charlottenburg, Germany, in comparison with the Hefner Alteneck Amyl-acetate lamp. In determining the candle-power the ratio of the English Parliamentary Standard Candle of 46 millimeters (1.773 inches) flame height to the Hefner lamp is taken as 1.14 to 1.0.
The comparison was made both when revolving at 180 r. p. m. and when the plane of the filament was 6o degrees from that of the center line of the photometer, on the line marking the 6odegree position toward the disc.
The best nine lamps are used as primary standards and are marked P-1, P-2, etc. The remaining nine are the secondary standards and are marked S-I, S-2, etc. From these standards 20 other lamps were standardized; they are known as the tertiary standards (marked T-1, T-2, etc.), and were made and selected for the purpose at the same time as, and are exactly like, the primary and secondary standards.
The standard lamps are handled by laboratorians only. Four primary, four secondary, and five tertiary standards are buried
FIG. 7 – Apparatus for vacuum test.
Photograph (page 29)
in an air-tight box to avoid loss of reference standards in case of fire. The secondary standards are checked with the primary standards every six (6) months, January and July and the tertiary with the secondary every month except when no lamps have been under test during that month. The Lumner-Brodhun screen is always used for these tests.
Whenever a lot of new lamps are to be tested one of the tertiary standard lamps is used as the working standard; a lamp taken from the lot will not suffice as, not being properly seasoned, its candle-power will not remain constant. In order to give the same amount of use to each of the tertiary standards they are used in rotation.
The Vacuum Test.—The vacuum test is made after the photometer test. The vacuum tester is shown in Fig. 7, and the manner in which a lamp is held while testing.
The tester is a Will-young X-ray apparatus. The induction coil, A, has its primary connected to an interrupter which differs from the ordinary type in being rotary instead of vibratory. The interrupter, B, is attached to the shaft of a Lundell 1/12 h. p. motor, C, by which it is driven at a speed of 1500 r.p.m, making 75 breaks a second, or three per revolution; the breaks are made under water, the interrupter being enclosed by a copper tank, T, for the purpose. The reversing switch, D, is connected to the primary circuit; it changes the direction of the current in the primary coil and interlocks with the motor switch so that the latter cannot be turned off with the reversing switch left at on point.
The condenser is of the ordinary type and made up of tin foil and paraffined paper. One electrode of the secondary of the coil is connected to an insulated metal plate, G, and the other to both terminals of the lamp, F.
The X-ray machine is regulated to give a spark of about three-eighths of an inch in length for regular lamps; for lamps of 5 c. p. and below a ¼-inch spark is used. The spark gap should be rather less than more than this. The terminals are, after the machine is regulated, set at a greater distance apart so that no spark passes between them.
The lamp to be tested is then held in the hand, grasping it by the bulb, and its base brought into contact with the metal plate, G.
If the vacuum is very poor the lamp will glow all through even before it touches the plate. If it is better than this, but still not good, there will be a glow all through the lamp when its termals touch the plate.
If the vacuum is good enough there may still be a considerable amount of glow, but it will all appear on the inside surface of the glass, and not at all in the interior of the lamp.
The glow in the interior of the lamp in the case of a bad vacuum will be of a blue color, or, if the vacuum is very bad, of a purple color. In the case of a good vacuum, when there is a glow upon the glass only, it will be blue if the bulb is made of lead glass, but of a green color if German glass is used. In the case of a good vacuum the glow on the glass is intermittent and only appears in patches or there may be no glow at all.
With a good vacuum while one hand holds the lamp to the plate the other hand may grasp the lamp, F, connected to the other terminal of the X-ray machine with impunity; while, if the vacuum is bad, a shock will be felt. The experiment is dangerous if the frequency is low.
The coil or inductorium test, while good, is not infallible. A lamp which shows a poor vacuum may, by being run very bright on the photometer for a minute or two, be made to show a good vacuum on the coil, no trace of any glow being perceptible. A Clouded appearance of the glow, as if the interior were filled with steam, is a sure indication of a bad lamp whatever the color.
A lamp which, when run at rated voltage, shows blue is a bad lamp and requires no farther vacuum test
The Life Test.—The life test is practically crucial as to filaments demonstrating the sufficiency of the construction by the test of endurance, the quality of the treating (flashing) by the amount of deposit on the interior surface of the bulb, and the integrity of the clamp under protracted heated conditions. The test also determines in a way the sufficiency of the vacuum, as with a poor vacuum the filament will soon burn out; but this particular fault would not be separable in a life test from poor construction of the filament.
The great problem of a life test is to keep the test lamps burning continuously at constant voltage over the interval of their useful life, that is, while their candle-power is reducing to80 per cent of the initial rated candle-power. Even with the expedient of burning at 3.1 efficiency the test will still require from 15 to 20 days (360 to 450 hours), day in and day out. Automatic regulation enables us to obtain very reliable results.
The life test apparatus is shown in Fig. 8; it was constructed at the navy yard. There are six lamp banks, A (two are not shown): four banks are for lamps having the standard base (150 C. 1), 32 c. p., and 16 c. p.) and can take 12 lamps each; a fifth bank can accomrnodate 48 1-candle-power instrument lamps, and a sixth bank, 48 5-candle-power instrument lamps. Each bank has an adjustable resistance, by which the voltage of the bank can be adjusted to the voltage of the mains; hence, 80-, 110-, and 123-volt lamps can be tested at the same time. The difference in actual voltage of the lamps on the same bank for the same rated voltage are adjusted by inserting small pieces of resistance wire in series with the connection of the particular socket, the wiring
Photograph (page 32)
FIG. 8 – Compensating Voltmeter and lamp banks.
being arranged to provide for it. These resistances give the lamps the voltage which produces an efficiency of 3.1 w. p. c. for each.
The voltage of the mains is kept constant by the automatic compensating voltmeter, C. The contact maker, D, is a long metal pointer which is pivoted at its upper end. At this pivot is fastened the armature of the electro-magnets and at such an angle with the main axis of the pointer that the armature will be in the center line of the electro-magnets when the pointer is at its extreme throw to the left. The pointer is electrically connected to the current of the line through the circuits of the electro-magnets which are shunted off the main line. In its motion from side to side the contact maker, D, closes circuits at E and F, which send a current through either one or the other of the two solenoids, G and H, of a relay; these attract their armatures, L, M, to which are secured two springs carrying two carbon points each, to make the connection double pole. When these carbon points come in contact with two other carbons connected in the main line, the armature of the motor, T, is energized. The motor turns a screw bar on which is a slider, S, moving over the surface of a coil rheostat, R, having two coils in parallel, and which is placed in series with the main circuit. (The apparatus as reconstructed has four rheostats with four sliders.)
If the voltage of the line should get too low, a spring draws the pointer, D, to the right, making contact to the right; the solenoid, G, is energized, its armature is attracted and the carbon points make contact with those connected to the leads of the motor armature; the motor then moves the screw bar in that sense which will reduce the resistance in the rheostat, R. If the voltage of the line becomes too great the electro-magnets of the automatic voltmeter will attract their armature on the contact maker, D, against the tension of the spring, contact will be made to the left; the solenoid H will attract its armature, and the motor energizes to increase the resistance of the rheostat, R. The reversal of the motor is assured by separately exciting its field by shunts from the mains.
At V is a Bristol recording voltmeter; a clockwork mechanism revolves a card marked on its outer edge in hours for 24 hours. The voltmeter pointer of the instrument presses on this paper, tracing a line in ink; volts are measured radially along the curves from the center. This voltmeter keeps an accurate record of the action of the automatic voltmeter.
Although this automatic apparatus is connected for 8 hours of the day on a power circuit, whose voltage is much disturbed by throwing motors on and off, its performs its duty well under the adverse circumstances. From 5 p. m. to 8 a. m. the line is fed by the comparatively steady source of storage batteries. The compensating voltmeter has during this interval to compensate for the small decrease of about one-half volt only; this ideal condition for the working of the compensating voltmeter is not available during the day owing to the necessity of charging the storage batteries. The sensibility of the compensating apparatus is such that it will operate on a change of two-tenths volt in either direction, insuring the great desideratum of a life test, steady voltage.
When selected for life test each lamp is given a serial or reference number, which is marked on the label. The number is also scratched on the brass base. This number identifies the lamp upon the records and throughout the test.
One lamp of each lot is laid aside to be used at the end of the test for comparing the blackening upon the inside of the bulbs.
Each lamp put on life test is first tested for vacuum.
The voltage of the lamps selected for life test is brought to that value at which the lamp burns at 3.1 watts per mean horizontal candle-power. Throughout the life test each lamp is burned at the particular voltage which was required to give 3.1 w. p. c. initially. The voltage to be used for an efficiency of 3.1 w. p. c. is obtained experimentally; it can be calculated approximately by the compound proportion, the total watts at the efficiency of the design as determined by the photometer test compared with the total watts at 3.1 w. p. c., the rated candle-power compared with that at 3.1 w. p. c., and the voltage as determined by the photometer test compared with the unknown, or that to be maintained for an efficiency at 3.1 w. p. c. In practice the required voltage is picked out from a previously constructed curve in per cent, but the curve must be made on a large scale to obtain the fractions of per cent incident to variations of one-tenth of a volt.
As before cited, photometer tests are made after a run of 25, 50, 75, and 100 hours and after every 100 hours thereafter until the candle-power has decreased to 80 per cent of its initial candlepower. The periods should be kept as close to 25, 50, 75, and 100 hours as possible. In case any run exceeds, 25, 50, 75, or 100 hours as the case may be, the next period is to be that much shorter so that no time accumulates. The average value of the candle-hour performance of the lamps subjected to life test must not be less than the amount shown in column 8, Table 2.
Adjust the compensating voltmeter and calibrate all other apparatus to be used during the life test. Be sure that the adjustment and operation is correct and make a trial run on dummy lamps for a day and a night before starting the test run. This will remove the variation due to heating of the coils of the compensating voltmeter and other apparatus. When a lamp burns out ascertain if the difficulty is with the filament of the lamp before removing it from the rack. Note and record the time at which the lamp burned out and if possible the cause. Save the lamp for a print to show blackening and location of defect in filament.
A new chart is dated and put in the Bristol recording voltmeter each day; the clock attachment being wound up at the same time. From time to time (preferably once a day) the recording voltmeter is compared with the standards. By means of an auxiliary resistance in series with the recording instrument, its calibration can be changed to conform with that of the standard when necessary.
As charts are taken off they are again dated and upon them a note is entered indicating the lamps burning during the time represented by the record.
The Bristol instrument is especially intended to record, by an irregularity in the curve, the elapsed time of any break in the circuit such as would be caused by a fuse blowing out or the operation of any one of the automatic devices for opening the circuit.
In case a lamp burns out during the night the potential rises owing to the change in current in the resistance coils, and a small irregularity will be noticed on the line of the Bristol recording voltmeter which records the exact time of the burning out.
The voltage of the lamps under test should be often checked and adjustment made upon the rheostats when necessary.
The lamp banks are made up of spring sockets so that the life test can be run with lamp filaments at any horizontal angle. As the test is now made the loop of the filament lays flat so that the drooping effect may be observed. Spring sockets also give a means of testing for the strength of cementing of the base of a lamp which must stand screwing up hard without breaking the base away from the bulb.
Heating of the clamp where the filament joins the platinum leading-in wires is a defect which is to be carefully watched during a life test.
The charts should be kept to constitute a complete check upon the "Time Log." The entries in the time log should be made each morning and evening and should contain notes of the condition of the test at the time and also a record of the times of opening and closing the circuit. The log is intended to be a record of the time the lamps have burned. If the circuit should be opened during the night the entry would be made from the chart of the recording voltmeter, but under no other circumstances should the voltmeter chart be used for making entries in the time log.
Voltmeters are kept in the lamp circuit during the entire run. Besides this, the photometer instruments consisting of voltmeter and ammeter are reserved for this work only. These instruments are calibrated at regular intervals and always before taking the photometer test at the 25, 50, 75, and Too hour intervals.
Method of Recording and Reporting Tests.
As the photometer tests are made the data are recorded. Each of the separate tests is averaged and entered up in the resume. The resume is intended to show the results of the test and is made up to represent the average of the lot of lamps under test.
Lamps.—The test is started with a certain number of lamps, and as these burn out the actual number left burning is recorded as indicated.
Average c. p.—The initial is taken as 100 per cent, and the actual is expressed in terms of it. The candle-power is the mean horizontal candle-power as measured by the photometer while the lamp rotates at 180 r. p. m.
Average w. p. c.—(Average watts per candle when running at the current and voltage determined by photometer.) The initial is taken as 100 per cent and the actual is expressed in terms of it.
The candle-hour performance of the lamps is considered as the sum of the candle hours given during each of the observed intervals, and up to that time when the lamp shall have burned out or shall have fallen to 80 per cent of its test candle-power.
Resistance.—The initial is taken at 100 per cent and is from the readings of current and voltage of lamps during the preliminary photometer run. The actual is computed from the data recorded.
From the resume data is taken to plot the following curves (Fig. 9)
- With time and c. p. (average) as co-ordinates.
FIGURE 9
FIG. 9 —Curves of performance on life test.
(b) With time and volts per rated c. p. co-ordinates.
(c) With time and w. p. c. (average) co-ordinates.
(d) With time and resistance (average) co-ordinates.
(e) With time and lamp hours (total) co-ordinates.
(f) With time and c. p. hours (total) co-ordinates.
The length of time a lamp burns is represented by the length of a line drawn parallel to the time co-ordinate, one time to represent one lamp.
It will be noted in Fig. 9 that the candle-power developed for the first 50 hours or so is greater than that for which the lamp is designed; this result is characteristic of all life tests and is the occasion for the prescription of 3 per cent in specifications.
After completion of the test all the lamps are mounted (or a selected representative number) with the one which was laid aside at the start, in receptacles on a block and a photograph made through them, preferably using an arc or a search-light for a source of light as the definition from this light is sharper and the defects in the filament and glass are better shown.
The lamp that was set aside should be mounted in the center and those that ran the longest disposed equally on each side; that that burned out first being at the ends.
The Target Diagram.—The Target, or "shotgun," diagram, when used in connection with the curves of Fig. 9, shows at a glance the results of the photometer and life tests of the test lamps. The diagram, Fig. 10, is constructed with candle-power and total watts as the co-ordinates forming a rectangle. The diagonals are the efficiency limits based on a mean rating of 3.5 w. p. c. As the upper left-hand and lower right-hand triangles are outside the prescribed limits the diagram represented by the contour line is really that used for reference.
The upper large black dot represents the mean for all the lamps as tested by photometer before the life test.
Each lamp of the test lot is plotted on the diagram by its serial test number in accordance with the results obtained on photometer test, and again from photometer results after life test; the same lamp in each case is then connected on the diagram by a dotted line to show individual performance, the slopes of these lines should evidently be the same. A mean position is also plotted which is derived from results for all the lamps, as in the case of the photometer test. This mean shows the general characteristics of the whole test lot submitted and also the particular feature in which the lot is lacking.
In order to obtain intelligent results from the diagram care should be taken not to construct it from a selected lot of lamps sent by a manufacturer; the test lot of the actual delivery is the, only good guide of performance, as selected lamps could be so picked out as to show quite different results from those determined by the test of the delivery.
FIGURE 10 (page 39)
CANDLE-POWER
FIG. 10 – The target diagram
CHAPTER 11
ARC LAMPS AND SEARCH-LIGHTS
The feature of arc lamp lighting is the great amount of light emitted from a single fixture, affording a decided advantage when large spaces are to be lighted whose height, or general use, renders the total required installation of incandescent lights difficult, insufficient and expensive in comparison; the spaces usually so lighted are fire rooms and engine rooms, and the arc lamps furnished a ship are on the basis of one lamp for each fire room and one lamp forward and abaft each main engine.
Arc lamps give very efficient lighting over coal barges when taking coal at night.
The type of arc lamp heretofore supplied, and known as the "miniature arc lamp," has been superseded by a commercial type commonly used for interior lighting and known as the "parallel rod, edgewise wound, direct current, enclosed arc" lamp. It is shown in Fig. 11. It operates at 43½ amperes and is adjustable for 80, 110, and 125 volts.
The advantages of the enclosed arc type over the open arc are: first, it can be run off the mains in multiple similarly to an incandescent lamp; second, it requires less trimming (putting in new carbons) for, while an open arc lamp will require the renewal of at least its positive carbon after burning for but from 12 to 14 hours, that of the enclosed arc will not require renewal under from 100 to 175 hours. The carbons of the lamp shown in Fig. ix, having a closed-base enclosing globe, will burn from 125 to 150 hours.
The mechanism is protected from dust, etc., by a bronzed sheet copper casing (Fig. 11), which is attached to the lower inner edge of the cap (at the top) by hook bayonet joints and held by set screws. To the lower edge of the casing is secured the clear glass outer globe which is protected by a guard, or cage, also secured to the casing. By loosening the thumb screws which hold the casing to the cap, and disengaging the bayonet joint, the casing together with guard and globe can be taken off clear of the inner (enclosing) globe and the mechanism.
The enclosing globe is of opalescent glass, is closed at the bottom and is held to the disc framing of the mechanism by screws under the globe flange. Its office is to exclude air from the carbons, having the general effect of increasing the voltage required to maintain the arc; for, while open arcs are generally
FIGURE 11 & FIGURE 12 (page 41)
FIG. 11 – Are lamp, Form 12, General Electric Company
FIG. 12 _ Mechanism of the Form 12 are lamp
maintained at approximately 50 volts, the enclosed arc requires an average of approximately 85 volts; this, of course, represents a loss of energy in comparison, for as two lamps in series could be run on a 10-volt circuit with a loss of but 60 watts for both, the enclosed arc system represents a loss of 180 watts for the single lamp; the convenience of branching off the enclosed arc type in multiple, its softer light and the material reduction in labor of replacing carbons has, however, caused it to largely supersede the open arc for street lighting and very generally for interiors.
The mechanism is shown in Fig. 12.
The current entering the electrode P reaches the slack positive wire A through the switch S; this wire is connected to a brass rod B which runs in a guide hole of the top of the spool of the rheostat C; on this rheostat is a ring or movable contact D, which can be set at any proper place on the rheostat C necessary to give that voltage which will give best working of the lamp; its effect is to connect the positive wire to that point of the resistance which will cut down the potential of the line, between the positive terminal P and the negative terminal N, to that potential at which the lamp is to operate; it is essential that the ring D shall be adjusted and set by the lamp makers in conformity with the voltage of the customer's supply line, and that it shall not be changed thereafter except by experts.
The rheostat C is made of bare, flat wire or ribbon and is wound on edge, each layer being insulated by a non-inflammable material; this, and the similar construction of the magnet windings, occasions the designation edgewise wound."
After passing through the flat windings of the rheostat C, below the movable contact D, the current passes to the windings of the two electro-magnets E, and thence by a slack wire F to the holder of the positive (upper) carbon I. The current then passes (by contact, or arc) to the negative carbon, thence to the clamp G and metal frame H, which holds the negative carbon, to a brass rod I, extending up back of the magnets, to a curved cross rod J that leads under the center of the rheostat C. From this point a straight connection leads to the negative terminal clear of, and through the center of, the rheostat.
The operation is: The entering current through P, A, D. and the rheostat C finally reaching N—energizes the two electromagnets E; these magnets draw up a horseshoe-shaped plunger K, which has a holder with bell-crank clamp L; this clamp grips the positive carbon as long as K is attracted into the magnet core and only releases it when resting on the disc frame which carries the enclosing globe M. The action of the plunger thus strikes the arc and starts the lamp. As the carbons burn away, the resistance across the arc increases, decreasing the current in the windings of the electro-magnets and hence the lifting power of those magnets; the resulting effect is that the positive carbon is lowered until the magnets hold it in proper relation to the resistance; that is, the magnets automatically adjust the distance to be maintained between the two carbons for steady burning and steady light. The guide rods 0 are in reality attached to the plunger K through the center of the electro-magnets, thus centering the plunger and keeping the axes of the positive and negative carbons in line; they are connected to a small dash pot (not shown) containing air only, which cushions any shock which might occur from a sudden failure of the current in the magnets and the consequent dropping of the plunger K.
When the switch S is opened the positive carbon descends slowly until the clamp L strikes the disc frame; the clamp then releases the positive carbon, which descends to rest on the negative, making an actual contact which is the necessary condition for the next starting up.
General Directions.—Only high grade solid carbons should be used in the lamp; the dimensions of the positive are 12 X ½ inch, and of the negative, 5 x ½ inch.
After unpacking a lamp, remove its casing, which is supported at the top by a bayonet joint. Loosen the thumb screw at the side of the top cap, raise the casing slightly and turn it to the left until it can be lowered. Take out all wedges and packing from the mechanism. Brush out any dust that may have accumulated, and examine the mechanism for loosened parts. Be sure that the movable parts work freely. Then replace the casing and the lamp will be ready for operation.
The lamps are usually installed on board ship by connecting to a switch and' receptacle through a length of double conductor, plain, and the ordinary attachment plug; the use of the switch S (Fig. 12) is therefore not necessary; the adjoining junction box contains the fuse for the lead. The binding post on the switch side of the lamp is positive and the attachment plug must 'be so entered into the clip of the receptacle as to insure this polarity; this is best accomplished by marking the contacts of the plug plus and minus and scribing the corresponding mark on the receptacle; if there is doubt as to which side is positive, insert the plug into the receptacle, let the lamp burn a few minutes and then switch off; the upper (positive) carbon should remain red hot longer than the lower (negative)—if the lower carbon remains red hot longer, reverse the plug.
The lamp should never be used without the enclosing globe, which excludes air from the arc. Closed base enclosing globes must rest squarely against the machined surface of the stationary cap. The number of hours the lamp will burn at one trimming depends largely upon keeping the globe tight and excluding the air.
As carbons vary somewhat in diameter, use only those of the dimensions specified. They should pass freely through the enclosing globe cap, for any friction at this point will prevent the proper operation of the lamp. The carbons must be smooth— sandpaper them if necessary, to remove small bunches of blisters.
To insure proper electrical connection to the positive carbon, it must be well inserted in the spring carbon-holder. Inserting carbons is facilitated by bevelling their ends. Better light will be obtained if the enclosing globe is cleaned thoroughly at each trimming.
Carbons are usually supplied in 12-inch lengths, the negative carbon being advantageously derived from the remainder of the positive after some use. Spare carbons should be stowed in moisture proof tins and care should be taken that they do not absorb oil.
Never use oil in the dash pot or on any part of the mechanism.
Inspection of Arc Lamps
Mechanical Construction.—The general workmanship in appearance, strength and adequate sufficiency of the various parts and the mechanism is rather a matter of comparison for the many details, comprising in each lamp some 36 parts apart from assembling machine screws. Principal points are as follows:
- The overall dimensions from inner edge of top of hook to extreme base of guard not to exceed 27½ inches; maximum allowable width at any part 8½ inches; maximum weight, 23 pounds.
The dimensions should be a minimum on account of the character of the locations for which the type of lamp is intended; the locations forward and adaft main engines is an especially contracted space; the limiting dimensions are those which are readily met by commercial types of construction.
2. The design of the lamp and its operating parts must be such as to adapt it for use in engine and fire rooms of naval vessels. This specification is to be considered with reference to the effect of the rolling, pitching and vibration of the vessel; the capability of continued operation when subjected to the moisture, dirt and oil incident to engine and fire rooms; and its capability of continued operation when exposed to weather, an experience to which the lamp will be subjected when used for lighting over coal barges when working at night. The determination of these matters rests mainly on the tightness of the outer and enclosing globe and the close assembly of the casing.
3. The top of the case is to be in one piece to form a watershed, and to have an insulated hook for suspension. The cap is usually so designed; note particularly that the suspension hook is insulated.
4. The case enclosing the operating mechanism shall be susceptible of ready removal, and replacement. The desirable feature should go farther than this and include the removal and replacement of the casing, outer globe and guard without disassembly of these parts; the proper method is explained in the description. This is not to be construed as meaning that the casing must be removed when the carbons are to be renewed; this is provided for in the next item.
5. To be fitted with a strong guard, bronze finish, capable of ready removal without the use of tools, and fitted with chains which will permit tbe dropping of the guard far enough below the enclosing globe that this globe can be conveniently removed in trimming.
6. The outer globe must be capable of being removed with the guard.
This does not preclude that they shall be separate, that is, it is not necessary that they be attached to the same ring with hinge design, etc. The globe requires to be separated for the cleaning necessary, at least, whenever the lamp is trimmed.
7. The lamp is to be designed to take at least a 10-inch positive carbon. The usual carbon is 12-inch.
8. The outer and enclosing globe are to conform to the official drawing, but are acceptable if interchangeable with the design of that drawing. The enclosing globe is specified to be of the light opal type; it is advisable that the opalescence be not too obstructive of the candle-power emissivity of the lamp.
9. Resistance material of the rheostat must be non-corrosive; the mounting must insure against sagging from excessive heating, crossed grounds or short circuits. Means for readily adjusting the resistance must be provided. The resistance is designed for adjustment over the range of 80, 110, and 125 volts of the supply line, but is not intended to be altered after once being adjusted for the voltage used in the particular ship.
10. Switches are not required, but if they are fitted they must be of the self-contained lever type, and accessible by use of a stick from the deck below.
A ring or hook must be a part of the design, to afford a means of suspension. Terminals for the line are to be fitted at the top and marked for polarity.
Electrical Qualifications and Test.—The lamp after unpacking and examination as to mechanical matters is connected up to a 80, 110, or 125 volt circuit, as the particular delivery may be specified, and the connections are traced to determine that the polarity as marked on the terminals is that of the connections. The cold drop of the magnet windings (for heat rise, see test of Generators) is then taken and the temperature of the resistance and casing is taken by thermometers, covering the bulbs with cotton. The current is then switched in and the lamp run for four hours, when the hot drop of the magnet windings is taken, and the temperature of the resistance and casing as before. The temperature of the air is noted half-hourly during test.
The permissible heat rise of the magnet windings is 60 degrees centigrade. There is no restriction as to the heat of the resistance or casing. (The low limit of 60 degrees is necessitated by the hot locations in which the lamp is to be used.)
2. While still hot a high potential test of 1000 volts (see test of Generating Sets) is made for one minute between the current carrying parts and the frame; these include the lead from the Positive terminal; the windings of the resistance; the winding of the magnets; positive carbon holder; negative carbon holder and frame and rod attachment leading to the connection at the base of the resistance; and the negative lead.
3. Test is then made of the adaptability of the resistance for adjustment for 80, 110, and 125-volt circuits by adjusting the movable contact on the resistance; the greater the voltage of the supply the greater the resistance to be introduced, and the higher the contact must be clamped on the rheostat. As lamp constructions differ somewhat the point at which, for a given voltage in line supply, the lamp operates best must be selected; lowering the contact clip increases the arc voltage.
4. During the four hour run an ammeter is kept in the lamp circuit and the operation of the current regulation, by the magnets noted. The observations should be frequent and the current regulation must be within five per cent.
5. Observations must be made during the four-hour test that the arc is steady and free of jump and flaming; the current variations (four above) are particularly to be noted if jump and flaming occurs (it is, however, more a matter of quality of carbons than of lamp operation).
6. A life test—a test of the carbons—is next made, the new carbons being allowed to burn continuously until the positive carbon is consumed. Tests usually show about 130 hours. General observations of the operation of the lamp are made during this interval.
7. The lamp must automatically cut the lamp out of circuit when the carbons are consumed.
If a life test is not made, this is tested by putting in a short positive carbon, and running the lamp until the carbon burns away.
Search-Lights
The varieties of projector usually met with in the service are of the manufacture of the General Electric Company or of the Schuckert Company. The sizes, rated by diameter of mirror, are 13-inch, 18-inch, 24-inch, and 30-inch; two 36-inch have been in use, and one 60-inch size has been installed.
The varieties (General Electric and Schuckert) have much in common, though differing in details; as a comparison in service experience, preference is often given to the General Electric Company's type of lamp on account of its good service and simplicity; and to the Schuckert Company's drum, or barrel, by reason of the opportunity of closure of the front of its drum by a shutter, or "Iris Blind," a convenient and advantageous arrangement for search-light exercise, as the focusing and adjustments may be made ready before the signal for exercise; also, at the expiration, the light can be masked and then lumed off without showing the glow; another advantage for navigating purposes is the facility of masking or using the light as required without delays incident to focusing, switching, etc. This is especially an advantage in torpedo-boat destroyers whose search-light must be placed low down, and whose use has a blinding effect on the officer at the conn, whether on the bridge or near the wheel.
[NOTE 3.—The General Electric Company has recently designed a shutter. It consists essentially of radial rods across the aperture of the drum to which light blades are attached on each side: the rods move together through gearing throwing the plane of the blades parallel with the beam when open: the device makes good closure against escape of light when the blades are across the beam.]
General Electric Company's Projector
There are two types of this projector manufactured by the General Electric Company, viz.: the "Electrical Control' and the "Hand Control."
Both types are alike in outward appearance, but the former type in addition to the usual electrical connections and training mechanism contains two shunt motors, each with their train of gears. This type, in addition, is provided with a controller, controller receptacle and a flexible cable to connect the controller to the receptacle. The controller, motors, etc., however, are not now generally installed. The 30-inch size, fitted for electrical control, is shown in Fig. 13.
[Non 4.—The electrically controlled projector, by reason of its convenient operation from advantageous locations for the operator and especially when the projector is installed in tops, is probably again to be introduced: the difficulties occasioning its removal from service were with the controller, from burning out and corrosion of the enclosed resistances, but incident to the lack of care on the part of personnel rather than to general inherent defects, the principal of which was that the interior was not well water-tighted; in the newer types of controller the defect has been remedied.]
The projector consists essentially of a base, fork, drum, mirror, obturator and magnet, automatic and hand feed lamp. The base consists of a casting drilled at the bottom to bolt
Figure 13 (page 49)
to the deck and to receive the line wires, which wires connect to the lower terminal of a double-pole switch secured to the base; the upper surface of the base has a track ring for the fork and drum to revolve upon, and to it are secured two insulated plungers with springs which act as conductors for the two leads which connect to the upper terminals of the double-pole switch.
The fork which supports the drum is composed of three castings; two arms and a turntable.
The upper end of the fork is fitted with bearings in which the drum trunnions work. The lower ends of the fork are bolted to the turntable. On the underside of the turntable the rollers are secured, which bear on the tracks of the base, and spring plungers in the base make electrical connection to two contact rings on the under side of the top of the turntable. From each of the contact rings a wire cable is led up to the lamp, and is secured midway, on the inner side of each arm of the fork by a brass clamp (see Fig. 13). The turntable of the electrically (changeable to hand-control) controlled projector contains a spindle surmounted by a cross-head with a special locking device of which: A is a hand star wheel for slow vertical movement; B is a wheel for throwing out a split nut, and is used for connecting or disconnecting the drum from the base mechanism; D is a hand star wheel for clamping the turntable to the center pin for engaging the electrical control. In the turntable of the projector having hand control only, all the gearing is omitted and only the hand star nut for clamping the horizontal movement is retained; the vertical movement being controlled by a hand star wheel on one of the arms of the fork and a quadrant fitted to one of the trunnions on the drum.
The drum consists of a cylinder, ventilators, mirror, front door frames, back cover and handles.
The cylinder is of sheet metal provided with three ventilators, two on the lower part of the drum to admit air; and one on top of the drum to allow the hot air to escape, and being so designed as to prevent entrance of wind and rain, or the escape and discovery of light; if to be located within 30 feet of the compass, the metal of the barrel and the securing rods should be specified to be of a non-magnetizable metal; experience in service shows this to be mandatory.
On one side of the upper ventilators is a focussing peep sight P, fitted with a lens and an enameled glass plate; on the latter the image of the carbons is reflected when the lamp is in operation and focus. A colored peep sight 0 is situated on each side of the drum, which permits of viewing the arc without dazzling the eye.
A trunnion is secured on each side of the drum, and two eye bolts, shown; one on each side, are installed on the trunnion blocks to facilitate transportation.
The mirror frame is of brass, lined with asbestos, and is fitted at the back with equally spaced springs which hold the mirror in place, allow for expansion due to heating and provide for flexibility under shock of concussion. It is secured to one end of the drum and protection to the frame and mirror against mechanical injury is provided by a metal cover secured to the barrel.
The mirror is of glass ground to parabolic curvature, silvered on the back, the silvering being protected by a close covering of hard paint. The mirror frame is designed to take either Mangin or parabolic mirrors; both types are in use, but for some time past the practice has been to use the parabolic mirror only, it having the advantage of less noticeable, and therefore confusing penumbra as compared with concave mirror types, and greater effective aperture as compared with the Mangin ; its distinct apparent advantage (as compared with the concave mirror) is that it lights up the foreground better and, as we are accustomed to outlining objects by their surroundings, the target is brought out with more sharpness and distinctness of outline.
The drum contains the mirror, obturator, drum slide contacts and the horizontal lamp. It has two handles E which serve to facilitate its manipulation when rapidity of movement is required. Two doors, M and N, are fitted to afford access to the carbons and the interior generally.
Front Door.—The opening of the barrel is closed by a door consisting of a ring having two handles (shown) and glazed with strips of plate glass. The use of the strips is more convenient and is more economical in affording a readier means of renewal after breakage by concussion, etc., than would be practicable for a solid pane.
The obturator, Fig. 14 (colloquially "shutter" but from which it should be distinguished), is suspended by a bracket as near to the arc as possible. It consists of an electro-magnet (magnetized by the current flowing through the carbons) and two semicircular brass shutters whose outer edges are hinged to a bracket; a clamp serves to hold the shutters in position when closed. The object of the obturator is to cut off those rays of light which would otherwise proceed in a cone directly from the arc without being reflected by the mirror into a parallel beam. The magnet consists of a broken ring of soft iron, curved to surround the arc on all sides except the top; its office is to counteract the tendency of the arc to force upward—thus burning away the carbon at the top and forming an imperfect and inefficient crater—a tendency which is created by the hot air currents rising through the barrel. The magnet can be rotated on its horizontal axis, this device contemplating its use to align the arc should it tend to the side as well as the top, a condition sometimes arising from imperfection in the carbons.
FIGURE 14 (page 52)
FIG. 14 – Obturator and magnet.
The drum slide contacts are secured to the inner lower part of the drum and to these contacts the cables leading from the contact rings are connected.
The controller, Fig. 13, is a sheet brass cylindrical cover attached to a composition base, with handles at the side for transportation. The latest type is much shorter than that of the figure and is fitted to be mounted on a bracket, or as convenient. Near the base is a coupling T fitted with recurvecl springs for electrical connection to the coupling attached to the controller cable. The resistance coils are in the interior of the case and ventilation is afforded around the rim of the cap. The controller (and hence the motors in the base of the projector) can be thrown in and out of circuit by the switch G. The handle H has a vertical plunger which makes contact with the motor supply lines (G being closed) to accomplish elevation and depression of the barrel and its motion to the right and left; the device admits of simultaneous operation of elevation combined with a motion to the right or to the left as desired, or of depression
FIGURE 15 (page 53)
combined with a motion to right or to the left; to elevate, the handle is raised; to depress it is pushed down; to move the barrel to the right the handle is moved to the operator's right, to move to the left, to the operator's left; to operate vertically and in azimuth at the same time, first move the handle for elevation (or depression) and, holding it in that position, move to the right or left; releasing the handle for any position attained leaves the barrel pointing in that position. The maximum permissible elevation is usually 40-degrees, the maximum depression 20 degrees; a train of the complete circle is practicable. The tube U just above that for the controller cable is capped and contains the fuse for the supply line of the controller.
The lamp, Fig. 15, is of the horizontal, automatic, ratchet feed focussing, type; it is remarkably compact, simple, and efficient in throwing the greatest practicable amount of effective light on the mirror. The obturator cuts off the direct rays and the magnet centers the crater to the center line of the mirror. The carbon carriers are designed for vertical and horizontal adjustment of the carbons; the automatic feed controls the crater at the focus until the carbons are consumed. The principal parts are described in connection with the operation of the lamp under automatic feed, as follows:
When the main switch S (Fig. 13) is closed, the current enters by the positive connection to the insulated plunger on the inner top of the base, thence to the contact ring within the turntable, and by the positive wire up to the drum slide contact within the drum; before closing this switch the automatic feed switch h (Fig. 15) must be closed, and the carbons set about one-eighth inch apart by a socket wrench shipped on the square post c of the screw bar.
The main current enters the lamp by the positive contact spring (shown in three leaves and a contact plate below c), insulated from the frame, which is connected to the winding of the series, or striking arc, magnet m. Since, on closing the main switch, no current is passing, the dead resistance of the rheostat has no effect in cutting down the voltage to that required for usual operation of the arc; and, the resistance of separation of the carbons, one-eighth inch, being small, the voltage across the carbons at the instant of closing the main switch is approximately that at the switchboard, hence the striking arc magnet receives a large excess current, attracts its armature, which (being attached to the upper screw bar) moves the carbon-holder, forming (“striking") the arc; the arc having been struck, the dead resistance of the rheostat—on passage of the current—cuts down the voltage to the operating voltage of the arc, about 50 volts, which voltage value is insufficient to maintain the attraction of the striking arc magnet for its armature; the armature is released, and the lamp thereafter controls the length of the arc by the shunt feed; the release of the armature of the striking arc magnet does not operate to approach the carbons by reason of lost motion of the nut of the screw-bar in its guide.
From the winding of the striking arc magnet m the current leads direct to the frame of the lamp, the whole lamp being insulated from the drum. From the frame the positive carbon (the larger in the figure) receives current directly through the carbon holder; thence the current crosses the arc to the negative carbon, and by its holder and a flexible connection to the negative lamp contact spring; thence to the drum sliding contact, wire connection, contact ring in turntable, a plunger, and flexible lead to the negative terminal of the switch S (Fig. 13). As the carbons (principally the positive) burn away the arc becomes attenuated, diminishing the luminosity of the crater, or the arc might break; to obviate this and trim the arc to proper length the automatic shunt feed is introduced consisting of the clutch magnet K and its operating parts.
The path of the shunt current is from the base of the lamp, through the contact of the circuit breaker 0, through the clutch magnet K and switch h to the negative lamp contact spring. After starting, the carbons being apart, the current flows only through the clutch magnet K and attracts the armature n, but in doing so, the circuit is opened at the circuit breaker and the armature returns to its original position, being pulled back by the regulating spring r, reclosing the circuit; the armature is again attracted and this movement will take place as long as the carbons are too far apart. It results from the fact that the efficient arc is maintained at from 47 to 50 volts; as long as the voltage, due to increased length of arc, does not attain a value of greater than 50 to 51 volts the armature of the clutch magnet will not be attracted and the feeding system remains inactive.
The movement of the armature turns the lamp feeding screws by means of the clutch p, to which it is connected, and at each stroke brings the points of the carbons nearer to one another; should the carbons come in contact, the main current passes through them, and through the arc striking magnet in, attracting its armature, and again striking the arc—this is, however, rare.
This armature s is mounted on the upper feeding screw and carries it along in its movement until the carbons are sufficiently separated to start the arc. After the arc is started, the clutch magnet k being in multiple with it will be traversed by a current proportional to the drop of potential across the arc. As the carbons burn away this drop increases gradually and the current through the clutch magnet k finally becomes strong enough to overcome the tension of the spring r and attract the armature n bringing the carbons nearer together. The regulation of the lamp is therefore adjusted by the tension of the spring r. If by accident or careless handling of the lamp the adjustment should be disarranged, the lamp would not burn at the right voltage at the arc; a voltmeter should be connected across the terminals of the lamp, and if the voltage is below the normal, tighten the spring r until the adjustment is right; tightening the spring increases the length of the arc and consequently the voltage; loosening the spring shortens the arc and decreases the voltage.
This adjustment should not be disturbed unless in case of actual necessity.
Operation by Hand Feed.—First see that the automatic switch h (Fig. 15) is open, and the carbons apart before closing the switch S (Fig. 13) on the projector base. To start the lamp, bring the carbons together and immediately separate them to about 3/8-inch. The carbons should be fed every half minute by means of the crank-handled socket wrench on the post (or through the tube L, Fig. 13) at the back of the projector. Start feeding when the length of the arc is approximately about ¼-inch.
To Place the Lamp in the Drum.—Firmly clamp the wheel B (Fig. 13); if the front door is in place remove and place it in box. If the lamp is carboned, remove the carbons. Open the obturator shutters and turn the magnet piece until the opening points downward. Take hold of the lamp by the handle a (Fig. 15) and casting b (never by the carbon carriers) and let the back end of the lamp rest on the drum slides, still holding the front end up, push until the lamp falls into the two slots in the slides, then lower the front end into place. Press the lamp against the focussing screw and turn the wheel until the lamp is caught and brought nearly in focus, i. e., when the front end of the lamp is level with the white line .marked on the drum. The sliding door can be opened to facilitate the operation. The magnet piece is to be turned down before placing the carbons.
To Focus the Lamp Whilst Burning.—It is not necessary to elevate or depress the beam for this purpose, though some operators regard it as more convenient; the vertical motion in this case should be elevation, and never more than 40 degrees; 25 degrees is a good and sufficient angle.
Move the lamp horizontally by means of the focussing screw. K (Fig. 13), nearer to or away from the mirror until the beam of light has its minimum divergence, which for the parabolic mirror is about 3 degrees; if the beam diverges move the lamp from the mirror, if it converges move the lamp towards the mirror.
To Place the Carbons.—Separate the carbon carriers v (Fig. 15) as far as possible by means of the brass crank-handled socket wrench, which is kept in the tool box; insert the wrench in the tube at the back of the drum and push it in until it fits on the square head of the lamp feeding screw c, then turn it in the proper direction for separating the carbon carriers.
Place the negative carbon in position with the end even with the carbon clamp and tighten the screw d sufficiently to insure good contact; then place the positive carbon with its point inch away from the negative carbon, and with the end projecting through the clamp, then tighten the screw sufficiently for good contact. Bring- the points of the carbons opposite each other by means of the vertical adjusting eccentric f and the horizontal adjusting screw g and close the obturator shutters.
Each carbon must burn evenly to obtain the best results, the negative burning to a point, the positive forming a crater in the center; if they do not they must be adjusted by the adjusting eccentric.
The Search-Light Rheostat
The single type is shown in Fig. 16. The type is not now used for other than 13-inch and 18-inch projectors, as rheostats for the larger sizes become large and have a dimension from front to back which renders them difficult to install in the locations required for convenient operation; in present practice the major part of the resistance is installed in one box and without regulating lever—this permits installation at any convenient place along the search-light wiring line—the remaining resistance is enclosed in a small convenient box, having adjusting facilities, at the location of operation (usually near the switchboard).
The rheostat (or rheostats) are installed in series with the line and their office is to cut down the voltage, "have a drop," equal to the difference between the voltage at the switchboard and the operating voltage of the arc; this drop is equal to the resistance of the rheostat multiplied by the passing current. The energy is dissipated in heat and amounts, for a 30-inch searchlight, to 5.7 kilowatts for each search-light, or for four, nearly 23 kilowatts, which approximates the total output of a 24 k. w. generator. The loss is severe and has occasioned the consideration of the introduction of a motor-generator for economy; but the intermittent and but occasional use of search-lights hardly warrants the extra device. The rheostats are classed by resistance, current capacity, voltage of the lamp, and line voltage respectively, as in the following example of a 24-inch projector; .62 (ohms), 50 (amperes), 50 (volts, lamp), 80 (volts, line).
Photograph (page 58)
The rheostat consists of a dead resistance and an adjustable resistance made up of German silver ribbon, the whole enclosed in a non-combustible frame. The value of the total resistance (hot) allows about four volts below to six volts above the best working voltage of the lamp, the exact voltage required can then be obtained by manipulating the rheostat handle (which controls the adjustable resistance) until a point is reached at which the lamp will work best; as long as the lamp works satisfactorily at this point, the rheostat handle should not be tampered with. The words "high" and "low" are marked on the rheostat face to indicate in which direction the handle is to be moved to obtain an increase or decrease in the voltage respectively.
The rheostat should be connected in the positive side of the circuit.
Schuckert Company's Projector.—The projector, Fig. 17, in its standard form consists of the following main parts:
Photograph (page 59)
Fig. 17. – 30 inch projector, Schuckert Company.
1. The foundation, or stand, with the ball-bearings for the turning-tables, the traverse for taking up the sliding rings and the electro-motors with the worm wheel axles.
2. The turning-table with the supports for the pivots of the drum, the gearings for the vertical and horizontal movement of the drum by hand, and the electro-motors (when electrical control is used), the sliding brushes, chain spanners and the clutches.
- The drum, containing glass parabolic mirror, lamp with device for moving the lamp, segment for centering the arc of light, "Iris Blind" (darkening apparatus), signalling apparatus, devices for observation and ventilation purposes, and further the necessary parts for the vertical movement of the drum, viz., the pivot, the pivot bearing and the toothed segment.
The stand consists of an upper part, the sheet-iron cone and the foot ring. These three parts surround the traverse which serves to take up the sliding rings and the electro-motors with their gearings. The upper part has a wedge-shaped groove, for taking up the steel ball rim, which serves as a bearer of the turning-table. The surface of the turning-table is level; a little further down, on the outside, is a grooved bracket on which the ball rim lies, and which centers the turning-table. At the inner side of the two ball rims an inner toothing is fixed into which work the raw-hide strips, which rotate the turning-table horizontally. The sheet-iron cone is coupled with the upper part; and the foot ring, and has two large openings for taking out the motors and two small openings for inner inspection. On the foot ring are four eyes -with holes for screwing the projector on the stand.
In the center of the traverse a bronze bearing is inserted into which a hollow shaft bears and into the latter a full shaft. Both shafts carry chain wheels on their upper ends, chain and worm wheels on their lower ends; the motor axles work into the latter and are provided with worms. The motors are completely enclosed and have ball bearings which rarely need oiling. They also have ears on both sides and are screwed on bolts which are fastened on the traverse.
The Turning Table.—The cast iron, cap-shaped, turning-table bears the projector drum which is carried on two bronzed arms with cap bearings; the table rotates the drum about a vertical axis. The table rests with its inner side on a steel ball rim which lies in a groove of the stand and is centered towards the latter by a second ball rim placed between the wall of the turning table and the stand; a center pivot is not necessary. On the turning-table are the enclosed gearings and coupling arrangements for the horizontal and vertical movement of the drum.. Both gears are so constructed that, by using a coupling nut for each, they permit free movement by hand and hand wheel; this is effected by the following arrangement. The vertical worm shaft works into a loose worm wheel, which is fixed on a hollow shaft, and on which the spur wheel, outside the drum, is keyed to cause the driving of the drum case by a toothed segment. On the hollow shaft is also placed a coupling disc which can be coupled with the worm wheel by turning the coupling nut as far to the left as possible.. On the other side of the coupling disc is a second loose worm wheel, into which the horizontal shaft with hand wheel works; this effects movement by the hand wheel. By turning the coupling nut as far to the right as Possible, the disc is coupled with this worm wheel and regulation by the hand wheel can be effected; for the intermediate Positions of the coupling nut, none of the worm wheels are coupled, hence a free movement of the drum can be effected by hand.
For turning the projector horizontally within the ball bearings, the stand is provided with an inner toothed device, into which gears a cog wheel which is placed on a vertical shaft, the latter bearing in the turning-table. Above the shaft bearing in the turning-table, a worm wheel is placed on the hollow shaft which can be coupled with the coupling plate on the hollow shaft by screwing down the coupling nut. By turning the worm wheel regulation by the hand wheel in a horizontal direction can be effected. In the intermediate positions of the nut, neither the chain nor the worm wheel is coupled, thus enabling the turning table to be moved by hand.
On the turning-table are sliding brushes which conduct the current for the lamp from the sliding rings which are fixed on the traverse of the stand; movable rollers are also placed on the table which are embedded in movable forks, these are for the chains of the electro-motive impetus.
Strong clutches are screwed on the turning-table, at angles of 120 degrees, which work underneath the toothed rim of the stand and thus prevent the table from tipping over when lifting the projector.
The drum consits of a sheet-iron case with a horizontal trunnion stiffened at both ends by rings, on which on the one end the glass parabolic mirror with cast-iron frame is placed, and on the other the "Iris Blend" and the front door. The trunnions of the drum and the optical center of the mirror fall together. On the bottom part of the drum is a guide on which the horizontal lamp (hanging on rail brackets) is fixed and through which the detachable carbon holders pass into the axis of the drum. This guide is uncovered by two flaps, leaving a small slot which allows the arms of the carbon holders to pass through and move easily. The lamp itself can be shifted with the carbon holders in the direction of the mirror axis, enabling the placing of the crater of the positive carbons in the focus of the mirror to obtain a concentration of the beam of light.
For the displacement of the lamp a screw spindle is fixed which leads to a worm wheel nut; this nut is turned through the worm by a hand wheel, effecting the movement of the lamp. In order to get at the inner apparatus of the drum and keep it in proper order, several doors are fixed on the drum which work into corresponding grooves of the drum and make a light-tight space.
To prevent the various parts of the drum, and especially the mirror, from getting unduly overheated, ventilation holes are placed on either side of the drum and a chimney on top. These parts are provided with a large number of cross blinds to prevent the escape of light and the penetration of rain and wind.
To suspend the drum, with the pivots in the bearings of the turning-table arms, the two drum rings on either side are connected with two steel rods, on which the pivot bearer is fixed in a movable way, thus facilitating the insertion of the pivots in the horizontal axis of equilibrium of the drum.1`
On the right-hand side, at the bottom of the drum, is the toothed segment which is used for vertical movement and for which purpose it gears with the corresponding flange rail of the turning-table through a toothed wheel.
The glass mirror, equally thick all over, is cut parabolically on both sides and has an inside diameter of no mm. and a focal distance of 310 mm. The mirror is silvered on the back (convex side) and then varnished; the edge of the mirror is embedded with asbestos paper in a cast-iron frame and held in position by a large number of elastic sheet-brass angles. The mirror frame
Photograph (page 63)
Fig. 18 – Lamp for 30-inch projector, Schuckert Company
is fastened on by screws and nuts, the former being screwed in the drum ring at the back.
To protect the surface of the mirror at the back, a sheet-iron cover with ventilation holes is fixed on the frame.
Darkening Device.—The "Iris Blind" serves as an effective screen or shutter for the search-light ray. The apparatus consists generally of two concentric rings moving towards each other, one of which is usually tightly fixed on the front edge of the search-light, whilst the other ring can be twisted against the former. To enable an easy rotation of this large ring, it is provided with a groove on its circumference and embedded in a corresponding groove of the solid ring by a steel ball rim. Both rings are connected with one another by thin, sickle-shaped, brass plates, in such a way that the latter are fastened with the pivots on the movable ring whilst the other ends are connected with the fixed ring in the pivots by a short rod. By turning the ring the various sheets are pushed fan-like over one another and thus close the aperture of the projector from the edge towards the center, always leaving an opening of circular shape, which is gradually diminishing; this process much resembles the action of the iris of the eye. A total closing of the center cannot be effected by the sickle-shaped darkening plates themselves unless made extremely sharp; two plate-shaped discs, or blind plates, are therefore fixed in the center in such a way that they form a pulley (with the bottom parts screwed together), with edge shaped groove, in which the sheets are pressed when closed, thus effecting a light-tight space. These blind plates do not absorb light even if the blind is open, as the center part of the mirror does not send out any useful light on account of the shadow of the negative carbon.
The "Iris Blind" is set in motion by a handle near the edge of the opening of the drum; a slit limits the distance the handle can travel.
Apparatus for Centering the Arc of Light.—To prevent a slant crater a segment of soft iron of about 240 degrees, concentric to the positive carbon, is fixed as near to the light arc as possible; the ends of the segment become magnetic poles to the current passing the carbons, thus creating magnetic lines of force. The latter diffract the arc until the crater is vertical to the axis of the carbon. The segment is supported by two sheet-iron
Photograph (page 65)
FIG 19 – Parts of the 30-inch Schuckert lamp.
bearers; it must be removed if the lamp is to be taken out, for which purpose the screw of the horizontal bearer is loosened and the whole put sideways round the lower jointed end of the other bearer.
Horizontal Shunt Lamp.—The lamp, Figs. 18 and 19, is automatic, but can also be regulated by hand, and in both cases be stopped before ignition; on the other hand it can be regulated either way while burning.
The automatic regulation chiefly consists of two magnet systems, one of which produces ("strikes") the arc when switched in, being called the striking arc magnet, whilst the other effects the pushing ("feeding") of the carbons when burning and is called the feed magnet. The arc former consists of a horse shoe shaped magnet, the arms of which lie in the chief current of the carbons. In front of the pole tips of this electro-magnet, an iron armature 3, Fig. 19, swings on two movable spiral springs which are fastened on the lamp wall. The worm shaft is brought in contact with the iron armature in such a manner that it is forced to travel the same way as the armature.
On the vertical axis 5, is a worm wheel 6, and a toothed wheel 7; the latter gears with the two toothed rods 8 and 9, which are fixed on small movable cars (Fig. 18); the carbon holder arms, jutting on the axis of the mirror, are insulated and placed in sockets of the small cars; the current is led direct to these arms by flexible cables and then to the carbons.
On the lower lamp plate is further placed the feed magnet 10, a horseshoe-shaped electro-magnet. The angle on - which the armature bears has on one side an insulated contact screw 11, on the other side the armature 13, with a contact spring; the armature is drawn towards the screw 17 by two screws and movable springs, thus causing the contact spring to come alongside the contact pin i8; the contact spring and pin lie, together with the magnet winding, in the shunt to the carbons. This shunt is interrupted to a certain degree as soon as the armature 13 is attracted by the magnet lo; the shunt is restored as soon as the armature is drawn off by the worm spring. On the armature is a trigger pin 19 which, when attracted, glides over the rack wheel 20 (the latter being fixed on the worm shaft 4), but, when going backwards, it drags the rack wheel along and thus causes a rotation of the worm shaft 4. This rotation is transferred to the toothed wheel 7 by the worm wheel 6 and thus causes the carbons to approach.
If the carbons do not- come in contact with each other when the current is closed the feed magnet begins to act; the automatic Opening and closing of the circuit causes the armature to swing rapidly, thus turning the back wheel 20, worm shaft 4, and toothed wheel 7, bringing the carbons together. As soon as the carbons touch each other, the current in the feed magnet 10 is no longer interrupted, the striking arc magnet 1 and 2, however, is strongly excited; consequently its armature is attracted and pushes the worm shaft, with worm wheel and toothed wheel, forward, the carbons are separated from each other, and form the arc of light.
As the burning of the carbons continues, the feed magnet becomes so powerful, owing to the increasing voltage, that it attracts its armature and overpowers the worm springs, until the automatic breaker interrupts the circuit, the armature drops back, sets the rack wheel 20, and also the worm and toothed Wheel in motion by the trigger pin 19, and the carbons approach each other. The approaching movement is very small in consequence of the worm transmission and takes place at small intervals, occasioning steady feeding. If the carbons have burned to a certain length, that is, if the toothed rods have arrived at their end position, the current of the feed magnet Jo is interrupted by lifting the spring 22 by a pin 21 on the positive toothed rod 9; the magnet 10 then ceases to work and the arc of light extinguishes slowly.
Hand Feed.—The automatic regulation of the lamp can be switched off and the feeding of the carbons be effected by hand; for this purpose the lever 23 on the rear of the lamp is set from A (automatic) to H (hand) thus interrupting the circuit of the feed magnet; the contact block 24 which forms the connection, is drawn away from the two springs. The pin 19 is then taken off by the ratched wheel 20, as the pin would hinder the free backward movement of the wheel 20. To bring the carbons nearer the focus, the small wheel 27 must occasionally be turned in the opposite direction to the hand of a watch. If the hand regulation is to be employed from the start, the carbons must first be made to touch each other by turning the small hand wheel 27, the carbons must then be quickly separated so that the arc light can attain its proper length.
A rheostat is supplied with the Schuckert projector, which is essentially the same as that used with the General Electric Company's projector.
Focussing.—On both sides of the drum are inserted round, dark, framed glasses which permit observation of the arc of light from the side. In order to control the position of the carbons from above, a little apparatus is fixed in the case, consisting of a mirror and a lens, which reflects an image of the arc of light upon a frosted glass inserted on the top of the case. The larger search-light projectors are also provided with a similar projection 'apparatus for the observation of the arc of light from the side, reflecting an image on the same frosted glass so that the images are placed underneath each other and by this means the proper insertion of the carbons is effected, as the axes fall together. In the center of the frosted glass is a vertical mark by which the positive carbon can be set in the focus of the mirror in the following way. The ray of the search-light is directed towards the sky at an angle of 20 to 30 degrees and the focus changed by shifting the lamp until the observer, who stands near the search-light projector, finds the beam sufficiently conically pointed (this is caused by the perspective, as the ray is slightly conically extended and drawing to a point should be continued until the ray appears to be shut in behind the point) ; the beam will then be that for the most favorable position of the crater towards the mirror and it is only necessary to bring the image to the mark of the frosted glass in such a manner that the crater edge and mark are in coincidence to obtain and retrace the right position of the crater by the mark.
Remarks on Care and Cleaning.—The lateral sheet-iron plate of the lamp case can be taken off, permitting access to the interior and an inspection of the gearing, flange rails, pulleys and toothed rods, also for a thorough cleaning with brush and rag.
For lubricating purposes, only the finest watch oil should be used and care must be taken, that it is entirely free from dust.
In handling the inner mechanism, the movable cables must not be damaged or displaced; the edged nuts of the cables must be well screwed on, but the ears on which the cables are suspended should permit of easy movement. Contact and worm springs on the armatures must not be bent. All contact parts must be kept metallically clean, and care must be taken that the nuts and screws are well screwed on.
If the apparatus is in constant use, it must be cleaned at least once a week. Ashes and particles of carbons which collect on the surface of the lamp, are not to be blown off, but are to be carefully brushed off towards the front or back.
Should the feed magnet already operate at a lower voltage than 51.5 volts, the springs have become too weak; this can be remedied by extending the screws until a voltage of 51.5 volts effects the regulation. Before the lamp is set to work, care must be taken that the carbons are of sufficient length; if new carbons are to be inserted, the carbon holders are extended to their fullest length by the small hand wheel 27; the screws 30 and 31 are raised, the carbons inserted and the screws slightly tightened up again. The Positive carbon is then adjusted by the two discs 28 and 29, the former of which serves for the horizontal, the latter for the vertical movements; the position of the carbons is correct when their axes are in the same line. The screws 30 and 31 on the carbon holders should be oiled from time to time. If old carbons are used, it will be advisable to file the two carbon ends into the shape which they tend to assume through burning; the carbons must not touch each other before they are switched in and care must be taken that a good crater is formed from the start. Should the arc of light become one-sided, it can be remedied by so adjusting the positive carbon by the discs 28 and 29 that the less used part of the crater of the positive carbon approaches the point of the negative carbon. For automatic regulation, it should be noted that the stop lever at the back of the lamp is set at A. The voltage at which the regulation of the lamp is effected is 51.5 volts; immediately after the lamp is switched in, it works at a lower voltage; when the carbons and wire windings have attained a proper rise of temperature, the feeding will be effected at the normal voltage of 51.5 volts.
General Notes on Projectors.—Dispersing, or diverging, lenses are no longer used.
The principle of operation of the search-light is as follows: With a current of sufficient strength passing through the lamp carbon electrodes, which are first placed in contact and then separated to about 1/8 inch, a brilliant arc is formed which consists mainly of volatilized carbon particles. The electrodes are consumed, first, by actual combination with the oxygen of the air; and second, by volatilization under the combined influence of the electric current and the intense heat. As a result of the formation of the arc, a crater is formed at the end of the positive carbon. The crater is due to the greater volatilization of the electrode at this point than elsewhere. It is the seat of highest temperature of the arc and is the main source of the light afforded. The major portion of the brilliant light emitted by the carbons is reflected by the mirror and passes out through the plain glass door (in the front of the projector) in a parallel beam.
The beam can be thrown horizontally in any direction, and vertically at any angle (within certain limits) by manipulating the hand control. Regarding the vertical movement of the projector: it is dangerous to keep the beam of light higher than 40 degrees above the horizontal for any length of time, as pieces of incandescent or hot carbon may fall on the mirror and cause it to break. It is only in case of absolute necessity that this limit should be reached or exceeded.
The clutch p (Fig. 15) of the General Electric lamp, being the only delicate part of the lamp, has been so located as to be easily removed and inspected.
It can happen that the clutch magnet will keep on working and yet not feed the carbons, due to the following causes:
1. The Feeding Screw Working Too Freely.—In this case the whole clutch would move backward and forward at each stroke instead of moving one way only. To remedy this tighten slightly the brake w at the back of the lamp.
- The Stopping of the Clutch.—In this case the clutch box would remain stationary and the lever work up and down without turning it; this would be due to oil or water inside the clutch. To remedy this, the clutch must be opened and cleaned.
In either of the above cases the lamp could be controlled by hand and would appear to be in working order.
- The Sticking of the Clutch.—This is due to dirt inside, in which case the lamp could not be controlled by hand. To remedy this, the clutch must be taken off, opened and cleaned. To remove the clutch, unscrew the nut fixing it to the feeding screw and take out the small pin on the end of the connecting rod; the clutch can then be pulled out. Open the cover by loosening its two screws, wipe all parts with a clean dry rag and put them back in place.
The two adjusting screws, in which the clutch lever rests when in place, must not be moved.
- If the carbons are left burning too near each other a mushroom will form at the end of the negative carbon and which will cut out a great deal of light. The mushroom must be broken as soon as it gets small enough at the neck to permit. To break it, move the positive carbon up and down quickly by means of the adjusting eccentric; bring the carbons to the center as soon as it is broken.
The mirror in the projector gets very hot, consequently great care should be taken not to let any cold air inside the projector drum after putting out the lamp, or while the lamp is in operation, as it might cause the breaking of the mirror. Before turning off the switch on the base of the projector, see that all doors are closed.
If the lamp is put out only to change carbons, the change must be made through the side doors, turning the projector so as to have the opening to leeward; the same course must be followed if for any cause the front door is to be removed.
To prevent damage to the obturator, the carbons must be removed from the lamp when placing it in or taking it out of the drum.
Use the wooden-handled socket wrench to tighten the carbon Clamps and also to work the carbon adjusting screws, should it become necessary while the lamp is burning.
The person in charge of the projector must never leave it while in operation; he must constantly watch the burning of the carbons and the focussing of the lamp.
The lamp must be kept clean and free from carbon dust, using the dusting brushes provided for that purpose. Do not blow the dust off. Take care no carbon dust gets into the lamp mechanism or clutch, also keep the drum contact slides and contact guides free from dirt and carbon dust.
Clean off the mirror and front door with a dry rag and polish with chamois skin.
The only parts of the lamp mechanism of the General Electric lamp to be oiled are the four bearings of feeding screws and the pivot of the armature of the clutch magnet. Clock oil is to be used; be careful to wipe off all the surplus oil. Do not oil carrier slides or clutch. Oil the trunnions and the working parts of the base. Do not oil whilst operating.
After every run, the projector should be put in condition for the next run. If the projector is not to be used again for some time, the canvas cover should be put over it.
Facing the switch on the projector base, the positive pole is to the left and the negative to the right.
There is often some little flaming of the carbons which cannot be controlled by the rheostat; it is unimportant except from the fact that it decreases the intensity of the light; it will usually disappear of itself. It occurs more frequently when the crater is not central in the positive carbon or when the carbons are not in exact line.
Some hissing will occur when starting up, especially with new carbons, and the lamp will not quiet down until a good crater has been formed in the positive carbon. This can be obviated by reaming out the crater in the positive carbon with a penknife before putting it in the clamp.
Flaming and hissing are promoted by inferior carbons and are much increased if the carbons have absorbed oil. Those now provided are of the Schmelzer or Electra manufacture and are very homogeneous; the positive carbon is bored axially and cored with a soft carbon, which materially assists in maintaining a good crater. Negative carbons have been sometimes cored, but this expedient is quite apt to conduce to the formation of mushrooms. In order to obtain the best results the carbons must be hard, homogeneous and of the best quality. Soft carbons fuse and cause mushrooms on the negative carbon which cut out a large portion of the light and prevent the arc from burning steadily.
The momentary current at starting, especially of short circuit if the carbons touch, is ordinarily heavy and quite sufficient to throw the pointer of the ammeter clear across the scale and against the stops; it need occasion no apprehension if it does not continue; if it does, the switch at the switchboard should be quickly opened. This starting current may be as much as so per cent above the working current.
Abnormal current shown by the search-light ammeter is often traceable to either a mushroom on the negative carbon or careless handling of the crank wrench. In most cases of fusing of the contact plungers in the pedestal there has been direct evidence of an attempt to regulate the feed by hand when the automatic gear was switched on. If the lamp does not feed it is for the reason that there has been a burn-out or difficulty in the automatic feed, or that the lamp itself is not clean, and in 90 per cent of the cases dirt is the cause; any attempt to remedy matters by use of a crank wrench, while the current is on, is quite sure to short-circuit the lamp and produce overload.
As a rule it is better to set the carbons before operation and permit no use of the wrench except in focussing. The automatic feed is a very desirable expedient and will give good report of itself if not impeded by an impatient use of the crank wrench. There is rarely any occasion for using the wrench on the screw bar after the lamp is in automatic operation.
The key to good search-light operation and management is thorough cleanliness in all the parts and frequent opportunity for Practice by those who are not ordinarily called upon.
The mirrors will spot or frost in time; the action is much hastened on board ship by the practice of exposing them to the rays of the sun while drying out the barrel. There is nothing that will so quickly ruin the silvered surface of a mirror as the action of direct sunlight. Keeping the cover on the projector too much causes sweating, as in the familiar example of the case of guns; it has an important effect in loosening the silvering (frosting).
Inspection of Search-Lights
Mechanical Construction.—The main points are: The base is to contain the electrical connections and be so arranged that it can be bolted securely to the deck or platform.
The turntable to revolve freely in a horizontal plane and indefinitely in either direction, or be clamped rigid.
The drum to be trunnioned on two arms bolted to the turntable, giving free movement in the vertical plane; to be designed to be rotated on its trunnions by hand, or clamped rigidly. The vertical movement to cover an arc of 70 degrees above or 30 degrees below the horizontal.
The front of the drum to be provided with a glass door composed of strips of clear plate glass; the door to be readily removable.
The drum to be thoroughly ventilated and fitted with peep sights for observing the arc in two planes, and to have hand holes for access to the interior.
All projectors to be finished in dead black, excepting working parts, which are to be bright.
The Lamp.—Operation The lamp is removed from the drum, and connected up with an electrical source of the same potential as that of the vessel in which the projector is to be used; usually 125 volts is the standard of test.
The rheostat, and an ammeter are connected in the positive leg (unless a shunted ammeter is to be used); a voltmeter is connected across the supply line, and across the carbons at the clamps of the holders.
Figure 20 (page 74)
The cold resistance of the magnet windings is then taken for calculation of heat rise.
New carbons are put in and the lamp is started in the usual way.
The voltage across the arc just before and just after starting should be noted.
The lamp is then burned for six hours or until the carbons are exhausted.
Note that the arc is well centered and that the motion is steady and even. Note the voltage and time whenever the feed begins to operate, and voltage when it stops.
Flaming should be slight; note its color.
Note any hissing or sputtering; the best condition is none of either; any sulphurous smell; there should be none; any chipping off of small pieces of carbon; there should be none.
The color of the carbon ash should be grey, not red; the amount of ash should be small.
Note formation of mushrooms on the negative carbon; good negatives should not occasion it; the time of burning out of the carbons, if less than six hours.
At the end of the run the drops on the magnet windings are taken whilst hot, from which the heat rise is calculated.
Insulation Resistance.—The insulation resistances of the lamp are commonly taken when at this stage as being more convenient than when run in the projector.
[NOTE 5.—The method of measuring insulation resistance which is always pursued is by the voltmeter method, which is quite sufficient for any laboratory or ship test.
Referring to Fig. 20, A and B are the positive and negative terminals of any supply line from the switchboard, and C, C, C are leading wires.
First: If the ends of the leading wires, E and F, are touched together, there will be a deflection in the voltmeter, which is the voltage of the supply line (neglecting resistance of leads).
Second: If E (or F) is touched to the conductor and F (or E) is connected to ground or to the adjacent metal from which the conductor should be insulated, there will be a smaller deflection by reason of the extra resistance of insulation between the conductor and the ground or the adjacent metal.
Neglecting minor resistances, the current passing in first above would be;
in which V is the voltage of the supply line and R is the resistance of the voltmeter.
In second the current would be (2) R + in which C1 is the current due to V and R Ri; RI being the resistance of the insulation. Since the deflections for the small arc of the voltmeter may be considered as proportional to the currents, we may substitute D and d for C and CI. Substituting, dividing, and clearing for Ri: (3) The insulation resistance (hot) which is usually expected is one inegohm. While voltages on board ship are those commonly used for ships' tests, Inspection voltages should be soo volts, as it has been determined by experiment that the resulting insulation resistances increase rapidly as the
(1)
in which V is the voltage of the supply line and R is the resistance of the voltmeter.
In second the current would be (2)
in which C1 is the current due to V and R R1; R1 being the resistance of the insulation.
Since the deflections for the small arc of the voltmeter may be considered as proportional to the currents, we may substitute D and d for C and C1.
Substituting, dividing, and clearing for R1 (3)
The insulation resistance (hot) which is usually expected is one megohm.
While voltages on board ship are those commonly used for ships' tests, Inspection voltages should be 500 volts, as it has been determined by experiment that the resulting insulation resistances increase rapidly as the voltage falls below 500 volts, and are unduly high at low voltages, while for 5oo volts and above the results are fairly constant.
The resistances of voltmeters are always marked on the instrument or on the case.
Often, as in testing, it is only desirable to know that the insulation resistance is at least one megohm; formula three above is then used in the more convenient form
Picture (page 76)
FIG. 21 – Grating test for mirrors.
R1 = R (D/d – 1)
from which, knowing R1 and D approximately, can be calculated the value of d for R1= 1,000,000 ohms: evidently this will be the highest value which d can have, and hence if the voltmeter under second above shows a deflection greater than this value of d, R1 will be less than one megohm: that is, the insulation resistance is not satisfactory.]
The measurements of insulation resistance to be taken for the lamp are: each magnet winding to lamp frame; positive contact spring to lamp frame; negative contact spring to lamp frame; lamp frame to ground (in the projector).
Carbons.—The test of the lamp covers most points in testing the characteristics of the carbons.
They should be hard and homogeneous; without cracks; be round; be straight within 1/16 inch for the entire length; and give a clear, metallic sound when struck.
It is usual to determine the hissing curve, for a particular type of delivery, as proposed by Ayrton ; the curves afford a ready graphic means of comparing carbons of different lots or makes.
Mirror.—Cover and Frame.—The mirror cover on the drum should be lined with asbestos to protect the operator from the heat; and, while being readily removable, should be capable of firm and secure assembly.
The mirror frame should have a large number of springs which will hold the mirror securely and centrally in place and afford good cushioning, against concussion and shock.
Glass, Silvering, and Backing.—The glass should be clear and free from blow holes and "stars."
The silvering should be even, smooth and free from blotches or frosting; these latter are readily detected by slanting the mirror in different positions.
The backing should be a hard, durable paint, unaffected by heat. It should assure perfect opacity when looking through; this is tested by holding the mirror against the rays of a strong light, an arc light is customarily used.
Curvature.—In this test the focal length is first measured. The mirror is exposed in a frame to the direct rays of the sun when the point of convergence will be immediately recognized and the distance to the mirror can be measured; if there is doubt, the Point of convergence can be searched by a piece of paper, which will take fire at the focus.
The mirror is mounted in a frame (Fig. 21), accurately Plumbed and accurately centered in front of the square hole of a partition on which is painted a large square, ruled off into smaller squares of about two-inch sides. A camera is inserted in the square hole of the partition and the ruled square illuminated by an arc light.
Fig. 22 shows the photographed results for a rejected mirror in which the lines clearly show poor workmanship in grinding toward the outer edges; for a good mirror the lines are quite straight and equi-distant.
Intensity.—The projector is mounted on a platform and directed at a to by 20 foot white target placed 4000 yards for 18-inch mirrors, 5000 yards for 24-inch, and 6000 yards for 30-inch.
The very best conditions of a clear, dark night must be chosen
Photograph (page 78)
FIG. 22 – Inferior grinding shown by test.
for the test; mist and fog interfere importantly with the penetration of the beam; in the latter case—fog—the beam will not penetrate farther than one or two hundred yards.
Under best conditions the target should show clearly and distinctly.
A further test of carbons, and operation of the lamp when in the projector, is made, after which the following insulation resistances are taken: plungers of base to base; positive and negative leads to base; drum contact springs to drum.
CHAPTER III
STANDARD WIRE
Wire for naval use is divided into three general classes:
I. Lighting Wire.—The wire for circuits leading to connections or outlets for which the electrical potential generated by the dynamo is to be used for lighting, or for the operation of motors or other apparatus.
II. Bell Wire.—A type for interior communication circuits which are to be operated by the lower voltage of primary batteries or dynamotors.
III. Cable.—In which single insulated wires are jacketed together or bound together into a circular cross-section for convenience in handling and running; the type affords a reduced ,.cross-section by the elimination of the braid on the separate wires, insures water-tightness particularly when many interior communication lines run through decks and bulkheads, and materially assists in localizing connections.
Construction of Wire
The general features of the construction of standard wire are illustrated in Fig. 23 and consist of:
I. A copper conductor, A, to give the required carrying capacity for the current which is to flow through it.
The smallest cross-section which will contain a given area is the circular, and wires are as a rule made cylindrical.
To obtain circularity of section and at the same time gain flexibility the copper conductor is made up of a number of evenly 'tinned, single wires of 98 per cent conductivity (compared with pure Copper), stranded in the so-called "geometric series" consisting of 1, 7, 19, 37, 61, 91, or 127 [1+6 X 1+6 X 2 +6X 3 +6X4+ 6 X 5 + 6 X 6, etc., having a summation, S = 3n (n — 1) ] single wires in two, three, four, or more layers. The circular construction is farther assured by winding each layer in the opposite direction to that of the last.
Drawing (page 79)
FIG. 23 – General idea of wire construction.
To insure maximum flexibility the pitch of the "standing" or "spiral" lay of all conductors so formed are not to exceed the following tabulated values:
Number of wires forming strand, Length of pitch expressed in diameters of individual wires.
Length of pitch
Number of wires expressed in
Forming strand diameters of individual wires
7 30
19 60
37 90
61 120
91 150
127 180
All single wires forming a strand are of the diameters standardized as the “Brown and Sharpe Gauge" as adopted by the American Institute of Electrical Engineers, October, 1893; they are designated by the cross-section in circular mils, a notation in which the circular mil is the area of a circle whose diameter is one thousandth of an inch. The circular mil notation gives a much simpler means of calculation than that involved in the usual method for the area of a circle; in the strand the total number of circular mils is the number of circular mils of the unit, single wire, multiplied by the number of single wires used for that strand.
Due to the twist in stranding, a longer length of single wire being necessary to form the finished strand, the conductivity of a strand is required to be only 95 per cent of that of pure copper instead of the 98 per cent required in the unit wires. It is practicable to obtain unit copper wires of 99 per cent conductivity.
2. Insulation of the copper conductor, B and C, is to prevent electrical leakage to surrounding material, in other words a protection against grounds, leaks, and short-circuits.
[NOTE 6.—A ground is an undesired connection from an electric conductor or contact to adjacent metal, etc. Its resistance may vary between wide limits, being practically nothing when metallic contact occurs. Its general effect is uneconomical waste of energy.
A ground upon one side of a system only will not affect its operation; that is, if a negative (or positive) wire be connected to the metal, to earth, no leak will occur; no current will flow, provided the positive (or negative) wire of that circuit is properly insulated: but if this positive (or negative) wire be imperfectly insulated, "have a ground" also, leakage and consequent loss of energy will ensue. A partial ground on both sides produces a leak, and a dead ground on both sides, a short-circuit.]
The wire insulation consists of two elements:
The first element, B, is a layer of pure Para rubber, which is taped or rolled on to a thickness of about 1/64 inch and is adherent to the copper conductor; it is the ultimate reliance for insulation when its vulcanized-rubber covering, C, cracks or flakes, and it becomes mandatory that this layer be of the finest grade of Para rubber, a variety which is the best of the commercial classification. The layer must be 98 per cent pure Para rubber, concentric, of uniform thickness, elastic, tough, and free from flaws and holes.
The second element, C, consists of a layer of vulcanized-rubber composition; the compound consists of the best grade of fine unrecovered Para rubber, mixed with sulphur and dry inorganic mineral matter only and containing from 39 to 44 per cent, by weight of fine Para rubber, and not more than 3 per cent, by weight, of sulphur; not more than two-tenths of one per cent of free sulphur is permissible. The layer must be concentric, continuous, free from flaws and holes, and must have a smooth surface and a circular section.
All vulcanized rubber compositions tend to farther vulcanization at any temperature, more rapidly at higher temperatures, until a hard, brittle composition results, in which condition the layer is easily flaked off or cracked; this points out the necessity of allowing an excess in the carrying capacity of' the conductor to Prevent undue heating and to the avoidance of overload on the circuit wires by installing lights or apparatus whose amperage was not allowed for in the original wire size. The magnitude of the effect on the insulation can be exemplified by considering the fact that the heating effect is C2R, and that, should the load be doubled, the heating effect would be four times as great; as the resistance would be greater due to heating, the insulation would be subjected to heating conditions over four times that for which it was calculated the completion of vulcanization would be materially hastened, and the undue heating would assist in producing cracking or breaking of the vulcanized rubber layer aside from mechanical injury in handling. There is another factor in the consideration which is that vulcanized products always contain an appreciable quantity of free sulphur; this free sulphur not only combines with the pure Para rubber layer, including it in the process of vulcanization, but it is also hygroscopic, introducing moisture into the interstices of cracked insulation to promote the occasion of grounds on the line, particularly when there is water in the molding or conduit. It is this injury to the pure Para layer which forms the basis of the restriction of free sulphur to two-tenths of one per cent; it occasions no especial difficulty to manufacturers.
3. A cotton tape, D, 1/32 inch in thickness, soaked with a rubber insulating compound; the tape is usually lapped one-half its width in laying on and is so worked as to insure a smooth surface and circular section of the rubber composition beneath, and must not adhere to the rubber. The especial office of this tape is to prevent any deformation of the smoothness of surface or circularity of section of the rubber composition, C, in order to secure a neat working fit in a standard rubber gasket, which is to closely fit on the layer, C, or over the outer braid and assure water tightness of the joint; measured dimensions "over vulcanized rubber" or "over tape" must come within 2½ per cent of tabulated values, the departure in no case to exceed 1/32 inch.
4. A braid, E, is principally to protect the construction beneath it from mechanical chafe and injury. Its size of thread and the number of threads (usually spoken of as "ends") are determined by the diameter to be covered. All braid must be clearly woven and, silk braid excepted, must be thoroughly saturated with a black, insulating waterproof compound, which compound will neither be injuriously affected nor have an injurious effect on the braid at a temperature of 95° C. (dry heat), or at any stage of the baking test, nor render the construction less flexible. Measurements "over braid" are required to come within 5 per cent of the tabulated values, the departure in no case to exceed 1/32 inch. There may be two exterior braids, but wherever a diameter "over outside braid" is tabulated or specified the outside surface must be sufficiently smooth to secure a neat working fit in a standard rubber gasket of that diameter (over outside braid) for the purpose of securing a watertight joint.
Lighting Wire
Lighting wire is classed as: Single Conductor, Twin Conductor, and Double Conductor. When greater conducting area than that of 14 B. & S. G. is required, the conductor is stranded in a series of 7, 19, 37, 61, 91, 127 wires, the strand consisting of one central wire, the remainder laid around it concentrically; each layer is twisted in the opposite direction from the preceding.
Single Conductor.
TABLE OF STANDARD DIMENSIONS
The above charts are on page 83
All single-lighting conductors are insulated as follows (Fig 24)
A layer of pure Para rubber, B, not less than 1/64 inch in thickness, rolled on. On the larger conductors this thickness must be increased, if necessary, to meet the requirements of the bending test.
A layer of vulcanized rubber C.
A layer of cotton tape D.
A close braid, E, to be made of No. 20 two-ply cotton thread, braided with three ends for all conductors under 60,000 circular mils, and of No. 16 three-ply cotton thread, braided with four ends, for all conductors of and above 60,000 circular mils.
FIG. 24 and FIG. 25 (page 84)
Twin Conductor
All twin-lighting conductors consists of two conductors, each one of which is insulated as follows (Fig. 25):
A layer of pure Para rubber, B, not less than 1/64 inch in thickness, rolled on.
A layer of vulcanized rubber, C.
A layer of cotton tape, D.
Two such insulated conductors are laid together, the interstices being filled with jute, G, and covered with two layers of Close braid, E and F.
Each braid is made of No. 20 two-ply cotton thread, braided with three ends.
Double Conductor.—Double conductor is classed as: Double Conductor, Plain; Double Conductor, Silk; Double Conductor, Diving Lamp.
Double Conductor, Plain.—The center conductor is constructed as follows:
A copper conductor, A (Fig. 26) consisting of seven No. 22 B. & S. G. wires, six of the wires to lay around the seventh.
A layer of vulcanized rubber, B, to an external diameter of 0.181 of an inch.
A close braid, C, of No. 60 two-ply cotton thread, braided with three ends.
The above form the core and the wires of the second conductor, D (seven No. 22 B. & S. G.), are laid around it over the braid concentrically and smoothly, the pitch of the lay is about VA inches.
Over both conductors is:
A close braid, E, of No. 60 two-ply cotton thread, braided with three ends.
A layer of vulcanized rubber, F, to an external diameter of 13/32 inch, to be vulcanized before braiding.
A layer of cotton tape, G, about 1/32 inch in thickness. A close braid of No. 30 three-ply linen gilling thread braided with two ends, H.
A close braid, I, of No. 30 three-ply linen gilling thread braided with three ends.
The finished dimension is 19/32 inch.
Double Conductor, Silk.—Each conductor is constructed as follows:
A stranded copper conductor, A (Fig. 27), consisting of seven No. 25 B. & S. G. untinned wires, six wires to lay concentrically around the seventh.
A close braid or wrapping, B, No. 80 Sea Island cotton thread.
A layer of vulcanized rubber, C, to a diameter of 4/32 inch.
A close braid, D, of No. 60 two-ply cotton thread. A close braid, E, made of hard-twisted olive-green silk.
Two conductors thus constructed ate twisted together to form the finished conductor.
FIG. 27.—Cross-section of double conductor, silk.
FIG. 28.—Cross-section of double conductor, diving lamp.
Double Conductor, Diving Lamp.—Each conductor is constructed as follows:
A conductor, A (Fig. 28), consisting of seven No. 20 B. & S. G. wires, six of the wires to lay around the seventh.
A layer of pure Para rubber, B, rolled on, of a thickness not less than 1/64 inch.
A layer of vulcanized rubber, C, to an external diameter of 0.186 inch.
Two conductors thus constructed are laid up or twisted together, and filled with jute lateral, D, to a circular section and an external diameter of 0.372 inch. The jute is saturated with an insulating compound.
Then to be covered with:
A layer of vulcanized rubber, E, to diameter of 18/32 inch.
A close braid, F, of No. 30 three-ply linen gilling thread, braided with three ends.
A close braid, G, of No. 30 three-ply linen gilling thread, braided with four ends.
The finished dimensions is 22/32 inch.
Bell Wire
Bell wire is classed as bell wire and bell cord.
Bell Wire.—Bell wire is constructed as follows:
A conductor consisting of one No. 16 B. & S. G. wire.
A layer of vulcanized rubber to a diameter of 0.113 inch.
A close braid of No. 40 two-ply cotton thread, braided with three ends to a diameter of 0.14 inch.
Bell cord, double, triple, and quadruple, consists of a twist of two, three, or four of the single wires specified for Double Conductor, Silk, and is used for wiring single, double, and triple pear push buttons. When bell cord, double, is required double conductor silk is usually used.
Cable
Cable is classed as follows: Interior Communication Cable; Cable for Night-signalling Sets.
Interior Communication Cable.—Each unit conductor (Fig. 29) consists of seven No. 24 B. & S. G. wires, G, the seven grouped to approach circularity of section; the whole is wrapped with No. 80 cotton thread, H, to a diameter of 0.068 inch, then covered with vulcanized rubber compound, F, to a diameter of 0.136 inch, then braided with No. 60 cotton thread, E, braided with three ends, the over-all diameter to be 0.156 inch.
FIG. 29 – Cross-section interior
Communication cable.
The requisite number of unit conductors, ten in the figure, to be laid up with a twist (having been filled with jute laterals, A, to approach circularity of section), then covered with:
A layer of cotton tape, B.
A layer of vulcanized rubber, C.
A close braid of No. 20 two-ply cotton thread, D, braided with three ends, for all cables of less than twelve conductors, and of No. 16 three-ply cotton thread, braided with four ends, for all cables of above twelve conductors.
One unit conductor in each cable of and under seven wires, and one wire in the inner and one wire in the outer layer in each cable in excess of seven wires has three adjacent black threads woven in the white braid.
Cable for Night-Signalling Sets.—Each conductor is made Up of nineteen strands (A, Fig. 30) of No. 25 B. & S. G. wire.
The insulation is made up as follows:
First. A laver of Para rubber, B, 1/64 inch thick rolled on.
Second. A layer of vulcanized rubber, C, to a diameter of 0.257 inch.
Third. A layer of 1/32-inch thick cotton tape, D, lapped onehalf width.
Fourth. A close braid of No. 30 three-ply linen gilling thread, B, braided with two ends; the diameter over braid to be 3/8 inch.
Sixteen conductors so constructed are laid up in the finished cable.
The cable is constructed as follows:
The heart of the cable consists of a continuous length of 9-thread, tarred, well stretched hemp rope, G; the Upper end of the heart extends beyond the end of the cable conductors and is finished with a neat, strong eye splice 3 inches in length.
Around the heart are laid five of the unit conductors the lay is spiral, with left hand twist, and of such a pitch as will closely assemble the conductors on the heart.
On the inner lay are laid the remaining eleven unit conductors; the lay is spiral, with right-hand twist, with jute filling, and of such a twist as will closely assemble the conductors on the inner layer.
The conductors are branched out for the lamps in pairs, using adjacent conductors; the reduction caused by branching is made in a neat taper by filling in with dead wire or jute; branching is first done from the outside layer of the cable and is spaced for 12-foot distance between the lantern centers, unless otherwise directed.
The outer layer of conductors is securely hitched with marline hitches, F, i inch apart, using a six-ply flax twine of about 1/8 inch diameter; the hitching is for the entire cable length.
In order to overcome induction from the aerial of the wireless, the upper end of the cable is closely served with No. 26 B. & S. G. iron wire, for a distance of about Io feet down, commencing 50 inches below the top of the upper lantern.
The lower, keyboard, end of the cable is fitted with a navy standard male coupling. The cable is furnished in special lengths, as required, the length being measured from the coupling to the first outlet.
Inspection of Wire
Quantity Delivered.—The length of wire on each reel is checked by running the wire through a registering counter, somewhat on the design of the counter of navigational sounding machines.
The end of the wire is taken between the swallows of two sheaves. The upper sheave is attached permanently to its axle, on which axle is a gearing which actuates a train of wheels moving a pointer over a dial, registering in feet. The lower sheave is larger, is also attached to its axle, but the axle journals in bearings set in a movable guide which has a vertical motion against a spring; this arrangement permits of accommodating the distance between the sheaves to varying diameters of wire; the spring also holds the lower sheave up against the wire, which in turn presses firmly against the upper sheave to avoid lost motion or slipping which would invalidate the dial indication; as the wire is pulled through it is reeled up on a horizontal reel whose posts are removable, leaving the wire coiled in readiness for the tank (for insulation resistance).
Test Samples.—From each reel is cut a 5-foot sample, which is divided up into five test samples as follows:
Sample No. 1, Three Feet Long.—This sample is used for all physical tests, not included under the chemical, baking, and braid tests, and also for the determination of the conductivity of the copper conductor. As the different layers are stripped off, the following are examined into:
That the diameters of each component layer of the construction, as prescribed by the tabulation, is correct, with special reference to that over vulcanized rubber and braid; these diameters are gauged on at least three planes to test the circularity of section. In order to insure water tightness, a rubber composition gasket is used as a packing which is designed to fit over the vulcanized layer or braid on the wire ( jacket of cables) ; the orifice of the gasket is exactly prescribed for a particular use, and it becomes mandatory that the section be circular and the diameter over the layers which are to fit in these gaskets be exact. The diameter over the outer braid of the finished construction is also important as determining the clearance which will be available when the wire is drawn in conduits; it is economical to draw as long lengths as possible, and undue stress on the wire must be avoided to prevent rupture or stress of the components of the wire construction through stretching; cables require especial care in this respect as regards the unit conductors.
That the waterproof insulating compound has thoroughly soaked the outer braids, determined by examining the inside surface; and that the proper number of threads (ends) are used and are closely woven. The number of ends prescribed are those which assure a neat fit over the underlying construction.
That the tape is thoroughly saturated with the insulating compound, and that it is smoothly lapped one-third to one-half. Tape layers are intended to act as a binding which will assure circularity of section of the vulcanized rubber layer which is to fit the gaskets, and to insure circularity for the braid; it is important that the tape does not adhere too closely to the vulcanized rubber. Tape should be carefully examined for folds or breaks which would produce roughness or imperfection of the vulcanized rubber layer. The insulating compound used on the tape is generally a rubber compound and is tested by burning a weighed sample; the characteristics required are rather waterproofing than insulating, the insulating is prescribed as it accomplishes both.
That the layer of pure Para rubber, next to the copper conductors, is uniform, free from flaws or holes, and, if taped, that the tape laps one-half, making the surface uniform. This determination must be made by examination of the longitudinal section and interior surface as, due to vulcanization from free sulphur, the line of demarcation between the pure Para rubber layer and vulcanized rubber is seldom distinct.
When the copper conductor has been stripped of layers, any adherent rubber is dissolved off with benzine and each wire composing the strand is examined for thoroughness and evenness of tinning, when so specified.
A length of one foot of all rubber layers is carefully removed in stripping for the determination of tensile strength and elongation, a test which is made in connection with the chemical test
Determination of Conductivity.—The sample of copper conductor is weighed, the weight being taken in grammes. Three of the unit wires composing each strand of the copper conductor are then separately tested for resistance in the X arm of a box of resistance coils arranged as a Wheatstone bridge and connected up with a Queen and Company's modification of the D'Arsonval galvanometer; the battery used is two cells (4½ volts) of an Electric Power and Storage Battery Company's accumulator. From the mean of the three resistances, and the mean of the weights of the three wires, the percentage of conductivity, as compared with that of pure copper at the temperature of 75° F, is determined by the following formula:
in which L is the length of the original conductor (3 feet) ; W is the weight of the length of the original copper conductor; R is the mean resistance of the three wires measured; K is the temperature coefficient, generally derived from a predetermined curve, which reduces R for the temperature of 75° F. This convenient formula is derived from the metre-gramme determination of Matthiessen for copper resistance at 0° C., and is calculated for the foot-gramme at 75° F., reduced to percentage of conductivity. Results of 99 or 100 per cent are latterly not infrequent for good wire.
Sample No. 2, Six Inches Long.—This specimen is placed in an oven, which consists of a sheet-iron box covered with a non conducting layer of asbestos wool; three steam coils inside the box vary the temperature in accordance with changes of steam pressure. A thermometer is inserted through an aperture in the top of the box. The front is provided with a glass door, through which the sample and thermometer can be observed. The temperature is raised to 95° C. At the expiration of four hours the specimen is cooled in the air and then sharply bent to a radius seven times the wire diameter; it should develop no breaks of cracks in either the braid or insulation and the compound should show no tendency to run out. The specimen is subjected to several similar tests over an interval of three days. For twin conductor the minimum diameter is the basis of bending.
Double Conductor, Silk, and Bell Cord are not baked.
Sample No. 3, Six inches Long.—The test of this sample is for determination of the water-repellent qualities of the outside braid and the tape. The ends of the specimen are dipped into hot paraffin; the specimen is weighed and is then submerged in water for 48 hours. When taken out it is again weighed, after drying the exterior surface, and the results reduced to percentage of absorption for braid and tape by subtracting the weight of the component layers of the wire which they cover. An absorption of 15 per cent is permitted.
Silk-covered conductors are not tested for absorption, as they are not expected to be waterproof.
Sample No. 4, Six Inches Long.—This sample is tagged and _ retained for future reference, especially with regard to re-inspection when occasioned by rejection.
Sample No. 5, Six Inches Long.—This sample is forwarded to the chemist and is tested: First, by microscope to determine as to cotton, linen, jute, and silk; the fibers are so distinctive for each that compliance with specification is readily tested without recourse to chemical re-agents or stains except as a check in case of doubt.
Second, for determination of rubber constituents. The analysis of rubber compounds consists in determining the following:
Extractive Matter, Saponifiable Matter, Mineral Matter, Vulcanized Rubber, Sulphur and Gum.
The Extractive Matter consists of resins, free sulphur, and sulphinated products.
Saponifiable Matter consists of rubber substitute.
Mineral Matter is the ash.
The Vulcanized Rubber consists of the gum and the sulphur.
The sample to be analyzed is digested with acetone for two hours it is then dried for about half an hour, cooled and weighed. The loss represents the extractive matter. The solution is evaporated to dryness, taken up in alcohol, and divided into two parts: one part is treated with concentrated nitric acid, allowed to digest on a steam bath, filtered, and the filtrate precipitated with barium chloride and allowed to settle over night; then filtered off and weighed, from which sulphur is calculated. This is the free sulphur. The other part is evaporated to dryness, taken up in neutral alcohol, titrated with fiftieth normal caustic potash; this, when calculated to abietic acid, represents the resins.
The residue from the previous operation is treated with 8 per cent caustic alcoholic soda and allowed to stand for 8 hours on the water bath. The alcoholic extract is then poured off and washed well with hot water, adding a little hydrochloric acid until neutral, and then dried and weighed. This weight, deducted from the previous weight, represents the amount of substitute present in the sample. This residue is ignited in a porcelain crucible and is calculated as mineral matter.
The sum of the extractive matter, saponifiable matter, and mineral matter, subtracted from 100 denotes the percentage of vulcanized rubber.
The total sulphur is separately determined: about one gramme of the sample is weighed into a 2-inch porcelain capsule and treated with a small amount of fuming nitric acid; when the evolution of gas has ceased the capsule is filled up with fuming nitric acid and allowed to stand over night; in the morning it is evaporated almost to dryness on the water bath. The residue is neutralized with magnesia, stirring with a small platinum rod and ignited, cold water is added and dissolved in hydrochloric acid ; it is now filtered and the sulphate precipitated with barium chloride. On standing over night the barium sulphate is filtered off, ignited, weighed, and calculated to sulphur. This represents the total sulphur. This sulphur, subtracted from the amount of vulcanized rubber, gives the percentage of gum. This percentage of gum represents the actual amount of chemically pure gum present; but as the Para gum contains an extractive value of its own, normally 2½ per cent, the 2½ per cent should be added to the amount of gum to determine the actual amount of gum used (to be 39 to 44 per cent fine Para).
In interpreting these results, the amount of extractive matter is the best guide to determine the quality of gum used. The evidences of regenerated rubber and rubber substitute are shown by high extractive values. If free sulphur has been found to be present it must be subtracted from the total sulphur before deducting the sulphur from the vulcanized rubber.
Asphaltum is detected in a rubber composition by treating the residue from the saponification with cold nitro-benzole for one
Photograph (page 95)
FIG. 31 – Riehlé testing machine.
hour. The nitro-benzole is poured off and the residue washed with ether; this residue is dried and weighed, the loss in weight representing the amount of asphaltum present. If asphaltum is present, the amount of sulphur in the asphaltum must be determined and deducted from the total sulphur, as in the case of the free sulphur. If substitutes are present, the amount of sulphur in the substitutes must also be determined and deducted from the total sulphur.
If an examination of the mineral part of the compound shows compounding with lead, the first precipitate of barium sulphate used in determining the total sulphur must be treated with hot concentrated nitric acid, washed with hot water, and the barium sulphate weighed off; this step is necessary to free the barium sulphate from lead sulphate.
Test of Tensile Strength.—The chemical test will not indicate conclusively the quality of the rubber used as regards age, that is, it will not entirely determine whether old stock, refuse, or reclaimed rubber has not been worked up in the composition, adulterations which would cause insufficient strength against stretching; to determine this the tensile strength and elongation of the vulcanized rubber layer is tested, as an adjunct to the chemical test, by the Riehlé testing machine shown in Fig. 31. (A more modern type is now actually used but the details are similar.)
The pieces which were stripped from the conductivity specimens are first carefully separated from their pure Para rubber layer and cut into lengths of 5 inches by 1/2 inch. Three specimens are selected for the test, their specific gravity determined, and the width and thickness calipered for cross-section. A specimen is then secured in the jaws, A, the distances between the markers, B, being set for two inches; the fiducial positions of the markers, B, are marked in ink on the specimen. A motor belted to the wheel of the screw-shaft, K, is set in motion, the screw bar giving a rate of separation of the jaws of three inches per minute. The screw-bar gears in the block, H, which is rigidly connected to the framing of the spring scale, G; the scale is similar to the circular-face scale used commercially for weighing, has a capacity of so pounds, and its scale registers one-tenth of a pound. The body of the spring scale travels on rollers; the tongue of the scale, F, is attached to the nearer jaw, this jaw being secured to a car moving on the roller, C. The hand wheel J, is for operating the mechanism by hand but the motor is preferable as the rate of separation of the jaws can be regulated as desired and is more constant. As the jaws separate, the markers, B, are kept to the original fiducial marks; a reading of the elongation in tenths of an inch is taken for every two pounds of tension shown by the spring scale. As the jaw, A, moves out on the roller, C, a wedge of sheet metal, D, drops down between the follower, E, and a lug on the car near C; this wedge, D, prevents a jar to the spring scale mechanism when the specimen breaks or tears, locks the car for the exact point of elongation, and also locks the pointer of the spring scale for the exact tension. The mean of the elongation and tensile strength of three specimens is taken, the test results of stress being reduced to the basis of the square inch. The prescribed breaking strain per square inch is not less than 1000 pounds per square inch and the elongation is to be at least 3½ times the original length between marks (that is, at least 7 inches). A second similar sample is subjected to a test for permanent set by subjecting it to a stress of 900 pounds per square inch (9/10 of specified breaking stress) for 10 minutes; the vulcanized rubber compound should be of such a character as to return to within 50 per cent of its original length at the end of to minutes after release from stretch.
Continuity and Insulation Resistance
Continuity.—The continuity of every copper conductor of each Parcel of wire is tested by placing each separate conductor of the reel length in series with an incandescent lamp and a switchboard using the lamp voltage. It is sometimes tested by "ringing through, using the standard magneto.
It occasionally happens that the conductor has been broken in course of manufacture, the case occurs-more often with interior-communication cables.
Insulation Resistance.—Each reel of wire is submerged for 24 hours in a large iron tank containing a solution of salt and water, 1½ pounds of salt to the cubic foot of water. Both ends of the Wire are left suspended above the surface of the water; the layers at the ends are trimmed back, exposing the copper conductor for about one inch, and the joint and trimmed portion is covered with paraffin. At the end of 24 hours after immersion the insulation resistance test is made by the direct-deflection method, a galvanometer being used instead of a voltmeter in this test.
Figure 32 (page 98)
series of brass blocks which can be connected to the bus bars through plugs, P; the middle block is connected to the metal of the tank. One end of the wire under test is connected to the block, A, through low-resistance leading wires which are clamped to the end of the copper conductor of the wire by a set screw. The lower bus bar is connected to a standard resistance of 4.95 megohms. The plug at A is first inserted at A' and the main switch (shown underneath the standard resistance) is closed; on closing the reversing switch a deflection is obtained due to the standard resistance alone, since the wire under test is cut out by moving P to A'. From this deflection the galvanometer constant is obtained:
Galv. Const. =4.95 X Deflection X Multiplying power of shunt. The plug, P, is now moved to A. On closing the main switch and reversing switch the cable is electrified and is allowed to charge for five minutes; the deflection obtained on discharge is due to the insulation resistance of the wire in series with the standard resistance, the resistance of connections being negligible in comparison. The insulation resistance in megohms per knot is then obtained from the formula:
(page 99)
The standard resistance is kept in series merely for convenience in retaining as permanent connections as possible.
In all finished constructions involving more than one conductor, each conductor is first tested to ground as above. The connection to the tank is then broken and both connections of Fig. 32 are led to adjacent wires of the construction to obtain the insulation resistance between conductors, tests being made each to each, and in the same manner as if to ground. Silk covered wires are not put in the tank; the coils are suspended in the air and only the resistance between conductors is tested.
The prescribed insulation resistance for different types of wire is shown in the following table. (The last column is the voltage for high crating potential test explained later under Inspection of Generating Sets.)
Test
Insulation resistance voltage
Lighting wire 30 minutes
Up to and including:
500,000 cm., single 1,000 megohms per knot 4,500
650,000 cm., single 900 megohms per knot 4,500
800,000 cm., single 800 megohms per knot 4,500
1,000,000 cm., single 750 megohms per knot 4,500
All twin wire:
Between conductors 1,000 megohms per knot 3,500
From conductors to ground 1,000 megohms per knot 3,500
Double conductor
Plain:
Between conductors 1,000 megohms per 1,000 feet 2,500
Each conductor to ground 1,000 megohms per 1,000 feet 3,500
Diving:
Between conductors 1,000 megohms per 1,000 feet 3,500
Each conductor to ground 1,000 megohms per 1,000 feet 3,500
Silk No test 5,000
Bell wire 500 megohms per 1,000 1,500
Bell cord No test 5,000
Cable
Interior-communication cable:
Between conductors 1,000 megohms per 1,000 feet 1,500
Each conductor to ground 1,000 megohms per 1,000 feet 3,500
Night-single cable:
Conductor for 1,000 megohms per 1,000 feet 3,500
Completed cable
Between conductors 1,000 megohms per 1,000 feet 3,500
Cable to ground 50 megohms per length 3,500
[NOTE 7.—These minima of insulation resistances are derived from experiments on the different compositions used and, in the case of lighting wire, the empirical formula commonly used for determination in thousands of megohms per knot is that of the rectangular hyperbola:
xy = .742
x being the insulation resistance required:
y being the diameter of the copper conductor:
0.742 being the diameter of the copper conductor of a 400, 000 cm. wire, for which the formula gives 1000.
The theoretical formula,
Page 100
in which D is the diameter over insulation and d the diameter over the copper conductor, is reduced by practical wire makers, after introducing common logarithms and the specific resistance of the rubber compounds Used in standard wire (at 72° F. for two minutes electrification), to the approximate form:
Ins. res. per knot = 10,000 log D,
d
which agrees very closely in results with that of the hyperbola above given.
These formulae show the following results:
For 4,000 cm 11,594 megohms per knot
“ 50,000 “ 2,921 “ “ “
“ 100,000 “ 2,044 “ “ “
“ 400,000 “ 1,000 “ “ “
“ 650,000 “ 794 “ “ “
“ 800,000 “ 706 “ “ “
“ 1,000,000 “ 620 “ “ “
As insulation resistance varies inversely as the contact surface of the rubber on the copper, wires larger than 400,000 cm. should be expected to maintain a test of about 700 megohms per knot instead of 1000. Formerly it was the custom to electrify a wire for only one minute, but a curve from experiments made at the New York Navy Yard shows that electrification of from 10 to 14 minutes give more characteristic results; the curve drops slowly after 5 minutes, and that interval has now been selected.
The effect of the voltage used for test has been mentioned, 500 volts being a desirable value.]
In the inspection of cables it is important that the wire in each layer which is specified to be covered with a braid containing White threads be so covered; the device is a necessity for connecting, tracing, and testing separate wires after installation.
CHAPTER IV
WIRING APPLIANCES
The general term "Wiring Appliances" is extended to include molding, conduit, insulators with their clamps, stuffing tubes, box tubes, terminal tubes, fuses, gaskets, tape, etc.; the strict interpretation is confined to devices intended for wiring connections for the control of current feed, such as junction boxes, switches, and the like.
The general term may be divided into four classes:
I. Ducts (including insulators).
II. The Box Types; usually watertight.
III. Non-watertight Types. IV. Auxiliary Appliances.
Ducts
Ducts afford the .most convenient method of protecting lines of wiring, and are divided into two general classes in ship-wiring molding, and conduit. The main distinction is that molding has grooves or channels made in wood, while conduit is some variety of metal or other pipe.
Molding—Molding is divided into two classes: molding for lighting-wire, and molding for bell-wire and cables; the varieties for each class are designated by the width.
In Fig. 33 A is the lighting-wire molding and B is the bell-wire molding. C is an especial type of molding sometimes used for the dynamo leads; the three-gutter portion is for the positive negative, and equalizer connecting wires which lead to the switchboard, the two-gutter portion is for the shunt-connecting wires leading to the 'rheostat.
Molding consists of three parts: that part containing the gutters for the wires, D, is called molding; that part upon which the molding rests, E, is known as the backing strip; and that part which covers the gutters, F, is the capping. The backing strip is usually ¾ inch thick; the width depends upon the number of lines of molding which are to be run over it; that is, if several lines of molding are to be run, side by side, the backing strip for those lines would be a board, ¾ inch thick, and of a width equal to the sum of the widths of the several moldings. When bolt or rivet heads, etc., jut out more than ¾ inch, the thickness of the backing strip must be increased. Backing strip is not used if the molding is to be run over a smooth or wooden surface. All capping is of the same width as the molding, and is 3/8 inch thick; to prevent warping it must be screwed to the side walls of the molding and not to the center wall.
Both molding and backing strip are made of thoroughly seasoned white pine; they are coated with white-lead paint after being fitted and before securing in place. When run over hard-wood
Photograph (page 103)
FIG. 33 – Types of ducts
surfaces all parts are of the same material and finish as the surrounding wood work.
The following are the standard dimensions of lighting-wire molding; bottoms of gutters to be semicircular in section:
For all feeders and wires of 60088 c. m. to 124928 c. m., inclusive- 3 inches wide, 1 ½ inch deep, including capping; to have two gutters each ¾ inch wide and ¾ inch deep, gutter separated by a ¾-inch wall; outside walls to be 3/8 inch.
For wires below 60088 c. m.—¾ inch wide, 1 3/8 inches deep, including capping; to have two gutters, each inch wide and q inch deep, gutters separated by a 34-inch wall; outside walls to be 3/8 inch thick.
The following table shows the standard dimensions of molding for bell wire; bottoms of gutters to be semicircular in cross section:
Depth Side
Width Inc. Capping Cutter Walls
Type inch inch inch inch
2 ¼-inch 2 ¼ 1 ¾ 1 5/8
2 ½-inch 2 ½ 2 1¼ 5/8
2 ¼-inch 2 ¾ 2 1/8 1 3/8 11/16
The use of molding is now generally restricted to the repair of installations originally constructed on the method. It is practically prohibited in the present policy of eliminating all wood from the permanent construction of the ship to minimize the risk of fire in action.
As a system it is inconvenient and objectionable for a variety of reasons, the chief of which are the following:
The large number of holes to be drilled and tapped, every 12 inches of length, to secure the backing strip. The drilling of beams for a passage for the wire, detracting from the beam strength; each hole drilled must also be carefully bushed with hard rubber. Changes of direction, or crosses, must be made by mitered joints, necessitating laborious and slow joiner work. No water tightness is assured except at connections, the mitered joints, capping, and fit at beams, leak; as the insulation afforded depends entirely upon keeping the molding dry, leakages through deck tubes readily introduces salt water. Many lengths of molding have been taken from ships which were charred through by a neighboring steam pipe, bake oven, galley, etc.; the carbon formed is not only a good conductor but is very hygroscopic; fireproofed woods are usually poor insulators, and corrode metal fastenings.
Molding is only fairly strong; it affords little protection to the wire from rough usage in fire-rooms or coal-bunkers, as it is easily torn down; it must follow the metal surfaces and cannot be run "flying." Where piping or some particular device requires much space up and down an engine- or fire-room bulkhead, the wiring must be led through to the opposite side, and generally into a coal-bunker; in these fire-room and coal-bunker locations, also subjected to clouds of dust and ashes, the use of molding has proved inadmissible.
Molding is sometimes permitted in quarters which are outside the watertight system of the ship; as the limits of the watertight system are generally defined to include all the ship construction below the stability (main) deck the use would be restricted to the upper deck cabins or wardrooms; it is also seen on some constructions where the wiring is run on insulators.
Conduit—The types of conduit specified are: Steel, enameled; brass, enameled, flexible. Specimens of the first and third are shown in Fig. 33. There are in use, also, the iron armored or lined conduit, and a flexible type consisting of covered rubber hose.
Steel, enameled, and brass, enameled, conduit (G, Fig. 33) conform in their metal construction to the dimensions for commercially standard steam, gas, and water pipes. On the dimensions of the following table 0.02 of an inch is allowed for manufacturing and loss of thickness in cleaning:
Outside Thickness Inside No. of
I.P.S. Diameter of wall diameter threads
Inches Inches Inches Inches
½ 0.840 0.110 0.620 14
¾ 1.050 0.115 0.820 11 ½
1 1.315 0.135 1. 045 11 ½
1 ¼ 1.660 0.140 1.380 11 ½
1 ½ 1.900 0.145 1.610 11 ½
Steel conduit is bought in lengths of 10 feet; brass in lengths of 12 feet.
Each length is threaded with a right-handed pipe-thread at each end, and one end of each length is supplied with a standard right-handed coupling of the same metal as the conduit length to which it is attached.
The interior surface of enameled conduit should be smooth and free from burs or fins; the bores must not be diminished in cutting; all ends should be faced square and the inner edges slightly beveled. The enamel is to be of not less than three coats, and is baked on, inside and out; Sabin's baking enamel is preferred for the purpose.
Steel conduit is used for the general installation throughout the ship. Brass conduit is used, generally speaking, in locations Where the use of steel is undesirable, such as magazines, shell rooms, ammunition-rooms, including their connections and approaches (steel is now commonly used, however); about (if near) compasses, especially the standard compass.
Iron-armored (lined) conduit consists of a wrought-iron pipe lined with a bitumenized paper tube 1/16 inch in thickness; a light cotton sheeting lining is sometimes placed between the pipe and the paper.
The type is not now carried in stock and is not replaced.
Flexible conduit (H, Fig. 33) consists of a spiral of insulated fiber over which is wound a heavy rubber friction tape; both are covered with a continuous woven jacket of cotton which is saturated with insulating compound and sprinkled with powdered mica. The particulars are tabulated as follows:
Inside Outside Feet to Pounds
diameter diameter coil per foot
Inches Inches
½ ¾ 200 0.125
5/8 7/8 200 0.140
¾ 1 150 0.175
1 1¼ 100 0.250
1¼ 1½ 100 0.280
For repairs on board ship 1½-inch hose answers very well; the best for the purpose is the double cotton-jacketed hose (I, Fig. 33).
The use of flexible conduit is confined to runs of wiring where the conduit will be subjected to a twisting strain, such as those leading to turret lights and apparatus. It is rarely used as the twisting can be accommodated by leading between boxes on the turret spindle, in other cases jacketed hose is preferable. In latest practice flexible conduit has entirely disappeared.
Conduit Fittings.—The fittings necessary to connect up a line of conduit conform in size to the conduits with which they are to be used; those for steel, enameled, conduit, unless specifically prescribed, are of steel, wrought iron, malleable iron, or cast iron, accordingly as the particular material is used in commercial practice for commercially standard pipes; those for brass, enameled, conduit are of the " beaded malleable" pattern.
Elbows (A, Fig. 34) are made of conduit, are bent 90°, in equal legs, and pipe-threaded at each end, externally.
I.P.S. Radius outside To fit in square
Inches Inches of side
Inches
½ 5 to 5½ 7¼
¾ 5½ to 6 8½
1 6 to 7 10
1¼ 7½ to 8 11 3/8
1½ 9 to 10 13 5/8
Outlet elbows, 90°, are constructed of the same material as elbows and are similar in appearance to those used for steam pipes; they are threaded internally, and are of the following sizes: Iron-pipe size, ½ inch, ¾ inch, 1 inch, 1¼ inch.
Outlet elbows, 45°, differ from outlet elbows, 90°, only in the angle of the bend, and are of the same iron-pipe sizes.
Long elbows (B, Fig. 34) are made of conduit and are bent 90° in unequal legs, externally pipe-threaded at each end.
(Photograph page 107)
FIG 34.—Types of conduit fittings.
I. P. S. Radius outside. To fit in rectangle side.
Inches. Inches. Inches.
½ 5 to 5½ 10 7/8 by 7¼
¾ 5½ to 6 12 by 8½
1 6 to 7 13¼ by 10
1¼ 7½ to 8 15 5/8 by 11 3/8
1½ 9 to 10 17 7/8 by 13 5/8
Couplings, plain (C, Fig. 34), are the pipe couplings to connect up the lengths of conduit and are continuously threaded internally. The sizes are: Iron pipe size, ½ inch, ¾ inch, 1 inch, 1¼ inch, 1½ inch.
The couplings may be right-handed, the thread running continuously from end to end, used for the general use of connecting up a line of pipe, and in which the coupling is first screwed to one length and the next length screwed into the coupling; or right- and left-handed, the thread being cut right-handed at one end and left-handed at the other, used for connecting up lengths of piping where it may be desirable to open up without taking down the line from either or both ends. The difference in use between the right and left coupling and a union is that unions are used when the pipe cannot be drawn (sprung) back; right and left couplings necessitate a separation of the ends by a full inch.
Couplings, reducing (D, Fig. 34), are similar to those used with commercial pipe, and are used when a change in size of pipe is desirable; they are threaded right-handedly, internally, and accomplish the following changes:
Iron pipe size: ¾ inch to ½ inch, 1 inch to ¾ inch, 1¼ inch to 1 inch, 1½ inch to 1¼ inch.
Unions (E, Fig. 34) are similar to commercial pipe unions, but the lip is ground off to facilitate springing apart the two lengths of conduit. They are used for separating a line of piping in lieu of right- and left-handed couplings in locations where the pipe cannot be forced back and the ends must be separated across the pipe end faces.
Nipples (F, Fig. 34) are made of enameled conduit and are externally threaded at each end; there are occasions requiring threading for the entire length. They are used as the connection of the conduit to various devices and as fitting pieces in finishing runs.
Graph (Page 108)
Plugs (G, Fig. 34) are similar to commercial pipe plugs, and are right-handed; the sizes are: Iron-pipe size, ½inch, ¾ inch, 1 inch, 1¼ inch, 1½ inch.
They are used for closing up the unused openings of appliances. Bushes (H, Fig. 34) are similar to commercial pipe bushes.
The standard sizes are: Iron-pipe size, ¾inch to ½ inch, 1 inch to ¾ inch, 1¼ inch to 1 inch, 1½ inch to 1¼ inch..
They are used where a smaller pipe is to be fitted into a fitting already tapped for a larger; they differ from a reducing coupling in that they are threaded both externally and internally.
Conduit should be used exclusively for ducts. Some of its advantages are:
The time and labor of installation is limited to drilling, without tapping, for hangers at beams only, or for straps at four or five foot intervals along flat surfaces, such as bulkheads, decks, etc.; changes of direction are made by bends or elbows which, except in long bends, require no fastening; one length joins the next through the commercial coupling. The drilled boles in beams and flat surfaces detract less from the metal strength than those for molding. It is watertight from the nature of the continuity of pipe joints and the screw joints at boxes, fixtures, etc. It is strong; it affords ample protection to the wiring where exposed to rough usage; it can be utilized as the pendant or support of a box or fixture; it can be bent clear of apparatus which interferes; it is fireproof; it affords good insulation as both pipe surfaces are covered with a good insulating material. The principal objection to conduit is its weight. In regard to the statement as to insulation, a qualification must be applied that the conduit be drained and dry; experiments show that if the dry enamel layer be examined with an exploring wire it will easily stand 2000 volts and the insulation resistance be high. If one end of a piece of conduit be embedded in paraffin and the tube be filled with salt or acidulated water, on inserting a wire into the water and again touching the metal of the conduit a low resistance or dead ground will result, showing that however well the enamel be put on, there are still minute interstices which affect or vitiate the insulating properties.
Insulators.—Insulators are made of glazed porcelain and a number, one for each wire run, are assembled together as shown in A, Fig. 35, which is the especial arrangement for lines of the larger sizes of wiring which are to be run along flat surfaces such as under decks and on bulkheads. The blocks of this assembly are square, in two parts, and are scored at each end for the securing bolts. The securing bolts are riveted into a base strip of bar metal whose width is the thickness of the insulator block, and their outer end is threaded for the nut which is set up on a round washer. Between the blocks and the metal base, and along the outer surface of the blocks, and underneath the washers, is placed a strip of 1/16-inch cloth-insertion sheet-rubber packing, which serves as a cushion against shock and gives a more even distribution of stress. At either end of the block assembly a post support is riveted to the metal base strip and finished at the outer end with thread, nut, and washer. The surface over which the base strip is to rest is tapped for two bolts which -secure the assembly in place.
Picture (Page 110)
FIG 35 - Methods of insulator installation
B (Fig. 35) shows another assembly of square insulators erected on an angle bar; this arrangement is used where the assembly is to attach to the angle side of bulkheads, beams, or projections which afford a flat surface for bolting.
C (Fig. 35) shows an assembly of round insulators, a convenient arrangement for attaching to beams, etc. One hanger has a flat surface for working next a single bulb beam, the other is curved and is of the type for working over double bulb beams; for channel beams a flat strap only is necessary. This assembly consists of a bar threaded at each end, over which the sleeves carrying the insulators and hangers are slipped, the assembly being set up by a nut and washer at the ends of the bar. The strap for holding the insulator in the sleeve is divided, the insulator being secured by a flanged-containing strap which is set up on each side by a screw tapping into the sleeve.
As the wire is strung along on the insulators it is left uncovered except in exposed places, where it is sometimes covered by a galvanized sheet-iron cover, bent to the dimensions rectangularly, flanged and secured by screws; the different lengths of covering are not fastened together, to facilitate removal.
The chief advantage of running wire on insulators is the saving of weight and cost as compared with either conduit or molding. If a sheet metal covering is provided, it is only used where the wire is especially exposed to mechanical injury. The method would not suffice for fire and engine rooms, store-rooms, or in fact any location under the protective deck, except wing passages, tiller or steering
PHOTOGRAPH (Page 111)
FIG 36 – Feeder junction box for conduit
rooms and sections of a platform deck; above the protective deck it is not advisable, except perhaps in quarters, owing to the likelihood of injury to the wire from gun gear, etc., and particularly from thoughtless handling which would stretch the wire or break its insulation. The use of sheet metal covering is probably unsanitary, by reason of the lodgement of dust and coal dirt, and as forming a retreat for vermin, especially that ship-pest, cock-roaches.
BOX Types
The use of boxes arises from the necessity of protecting, watertighting, and fireproofing circuit connections, and box types for other than interior communication lines receive their name from the particular method of connection desired as determined by the interior fitting which the box encloses.
All boxes consist of two parts, the box proper and an interior fitting.
The Box Proper.—That for conduit (Fig. 36) consists of a cast composition shell and a cover. The sides and ends of the shell are reinforced by bosses, cast in one with the shell, which are drilled and tapped for the size of conduit appropriate to the size of the wire which is to be led in; the extra thickness of the bosses gives the length of thread required for a strong, good joint.
On the inner bottom of the shell are cast small bosses which are tapped for the screws which secure the interior fitting in place. To insulate the interior fitting and screws, if loosened, from the metal of the shell, the interior of the shell should be painted with Sabin's enamel ("Sabine ") ; a sheet of mica, 25 mils thick, and of slightly greater dimensions than the insulating block of the interior fitting, is fitted over the bottom bosses: the mica also affords a slight cushioning effect against shock, and affords a long surface of insulation.
PHOTOGRAPH (Page 112)
FIG. 37 – Feeder junction box for molding.
The outer edges of the shell are tapped for the prescribed number of screws which will hold the cover securely without warping.
In the box walls are drilled and tapped the screw wells, in which are driven the screws which secure the completed appliance at its location in the ship. The nature of the pipe assembly is sufficient in most cases to hold the box in position without the screws in the screw wells; to preserve water tightness; the screw well masses are never drilled unless the appliance must be secured by the screws.
For installation where molding is the duct the type of box for similar use as Fig. 36) colloquially known as the "Navy Standard Box" is that shown in Fig. 37. The difference is that stuffing tubes are inserted at the sides and ends of the box in place of the bosses shown for the conduit box (Fig. 36). The stuffing tubes are threaded for their entire length and are screwed into the wall of the box and braised. On the outer end of the stuffing tube is a gland whose office is to set up the conical rubber gasket which packs the wire watertight; the stuffing tubes are reamed to take the conical shape of the gasket, and inside the gland is a small brass washer ring without which it would be impracticable to turn the gland against the friction of the gasket. In other details the box for molding and the box for conduit are alike and both types are made for all the varieties; the covers are identical.
The box cover is sawed out of sheet brass. The screw holes are drilled by jig. The cover is cut for the apertures adapted to the particular name of box. The whole of the inner side of the cover is lined with cloth insertion sheet rubber packing, cemented on to prevent stripping when the cover is removed. The packing takes on the box edges and closes the joint watertight.
The Interior Fitting.—While each type of box appliance has an interior fitting peculiar to itself, the following are general features common to all interior fittings (except those for interior communication lines).
I. The insulating block on which the circuit connections are assembled is made of vitreous, unglazed porcelain.
II. The interior fittings of all boxes of the same name whether for molding or conduit are identical.
III. All current carrying parts of interior fittings are of copper (usually stampings) of 96 per cent conductivity.
IV. All current carrying parts must be exposed and not embedded in the porcelain.
The few exceptions to these general rules are noted under the respective cases.
The names of the different types of box on other than interior communication lines are:
Junction box.
Distribution box.
Switch.
Receptacle.
Switch and receptacle.
The Junction Box
This type, commercially known as a cut-out, affords the means of tapping off current from the feeders leading from the switchboard to the mains and sub-mains, or from these latter to the branches which feed the outlets for lights, etc.
There are four classes of junction boxes:
The Feeder Junction Box (F. J. B.).
The Main Junction Box (M. J. B.).
The 4-Way Junction Box, or Branch Junction Box, 4-Way (B. J. B. 4).
The 3-Way Junction Box, or Branch Junction Box, 3-Way (B. J. B. 3).
All junction box interior fittings have their porcelains of dimensions, least, 3 9/16 by 1i 13/16 by inch; the clearance holes for securing by No. 6 screws to the bosses in the bottom of the box are 3¾ inches between centers. The rule previously to 1902 was 31/8 inches; the new rule is established in order to have all porcelains interchangeable, those for conduit boxes having been established at 3½ inches. The old type of porcelain (3 1/8) can be used on a 3¼-inch center by slotting away.
All current carrying parts of the interior fitting which are of opposite polarity are to be separated from each other and from the walls of the box by at least 1/8-inch.
Feeder Junction Box.—Feeder junction boxes are for tapping off current from the feeders leading from the switchboard to mains and sub-mains only and are always made three-way, one single (or double) entrance and one single (or double) outlet for the feeder at the ends, and an outlet for the main, or sub-main, at the side.
There are two sizes of standard conduit feeder box; one which is known as Feeder Junction Box for Double Conduit, and to be installed when the wire size of the feeder is above 60,000 cm. and up to 150,000 cm.; the other when the wire size is 60,000 cm. (30,000 cm. for twin conductor) or under; the governing cause of difference in type being the number of conduits necessary for the wire size of the feeder, two conduits for the larger sizes and one for the smaller.
Figure 36 shows the smaller size of box for conduit work. The larger differs in having two bosses on the ends, one for each of the legs of the feeder, positive and negative; small size wires can be run in one conduit, tapping into the smaller size box. The screw wells are tapped near the corners of the box and are sunk into the walls without masses. The cover is secured by six screws, one of which takes the chain of the screw cap.
The screw cap is lined with cloth insertion sheet rubber packing cemented to the inner side of the top, and is recessed for the wrench; the chain is held by a round-head-rivet post.
The interior fitting is a double-pole, single-branch block rectangular in shape.
One through circuit connection is led straight, the other is bent in to avoid the two side connections, all are secured to the porcelain by screws whose bottom ends are in recesses of the block. In one with each connector and side connector is a vertical
PHOTOGRAPH (PAGE 115)
FIG. 38 – Special Feeder junction box, conduit
flanged projection on which rests a mica cup; the office of the cup is to prevent the spreading of the metal when a fuse blows, the cup protecting all of the fitting except the fuses and their contact screws. Only the side leads are fused, that is, there is no break in the feeder line. The fuses are of the copper tipped commercial type and bent as shown.
The two small copper connectors shown at the top of the figure are supplied to bridge across the fuse gap, to make through connections to the main or sub-main, when the branched wire size is to remain the same and does not require fusing, or when a sharp branch in a feeder line is to be made for which pipe bends will not answer. The copper connectors are secured to the fuse contact screws; the fuse and mica cup are then omitted. The wires are secured to the connectors by a clamping, binding strap with recess in both strap and connector.
Special Feeder Junction Box, or Feeder Box for large currents.
This type, shown in Fig. 38, is for use on heavy power circuits carrying from 400 to 500 amperes. It is much larger than other types -of feeder box and has a large boss at one end, and two on each side near the end, to be tapped for leading in the wiring. The bottom of the box is covered with 1/8-inch micanite as insulation to the interior fitting.
The interior fitting block of porcelain is held to bosses on the interior bottom of the box by two screws, and to the block are secured four current carrying parts of copper—ordinarily of cast copper—having a sufficient cross-sectional area for carrying 450 to 300 amperes; the two contacts, near the leading in end of the box are copper blocks, secured to the porcelain by screws, and having binding straps for securing the wire; the other two contacts are longer connectors and curved that the wiring may pass well clear when entering to pass through the side bosses. The two sets of contacts are separated by one inch and arrangement is afforded for bridging the gap by a heavy (dynamo type of) fuse. To the inside cover of the box is secured a micanite plate which extends down between the fuses of the box to prevent arcing across. The cover is lined with cloth insertion sheet rubber packing.
[NOTE 8.—Micanite is a term used commercially for assemblages of mica in cement, it being impracticable to obtain mica in requisite thickness. One method of construction is to stamp out thin sheets of mica into convenient shapes and area, these are then built up with cement and pressed into a slab of desired thickness which can be cut or machined. The construction does not absorb moisture and is but slightly affected by oil, giving good insulating properties.]
Search-Light, or Main Junction Box.—This box is rarely used. It was intended as a through connection, to avoid splicing, in a long feeder line when the feeder wire had to be cut by reason of mechanical difficulties or probable injury in drawing; pulling sleeves obviate cutting even the longest feeder and the small carrying capacity of the box renders it inadvisable for the purpose.. The box has sometimes been used on a search-light line for connecting in the search-light leads, but it is not necessary except in the cases of alterations where a detour is made, necessitating the insertion of an extra length of conductor.
The conduit type is shown in Fig. 39. The box is similar to the feeder box but without a side boss.
The cover is without opening and held by six screws.
The interior fitting has two through connectors with binding straps at either end.
Branch Junction Box.—The branch junction box, 4-way or 3-way, is for tapping off current from mains or sub-mains to
PHOTOGRAPH (PAGE 117)
FIG. 39 – Main junction box, conduit
the branches leading to outlets for lights, etc., only. The wires of the mains (or sub-mains) are led in at the ends and the branches led in at the side; if it is necessary to branch in on both sides a 4-way box is installed, if on one side only, a 3-way. It is intended that the side leads shall be for single wires of not greater size than No. 14 B. & S. G. (4017 cm.).
The conduit, 4-way type, is shown in Fig. 40. The 3-way
PHOTOGRAPH (PAGE 117)
FIG. 40 -4-way branch junction box, conduit
differs in having a boss on but one side instead of the two sides as shown.
The cover and wrench are the same as for the smaller size of Feeder Box; the screw wells are similar.
The interior fitting has two through connectors for the wire main with binding straps at each end. The side connectors are run across the block so that either or both sides may be branched.
On each through and side connection is a vertical to which is screwed a clip, protected by a U-shaped guard, the clip and guard assembled on the same screw. Into these clips are pressed the glass tube fuses for the branches. The cross-section of the current carrying parts is 30,000 cm. The clips are of phosphor bronze.
Distribution Box—The object of the distribution box is to avoid the installation of so many branch junction boxes on a main in those locations (such as fire and engine rooms) where it is practicable to distribute to a number of outlets in nearby
PHOTOGRAPH (PAGE 118)
FIG. 41 – 8-way distribution box (cover not shown)
locations from one central point. The distribution box collects these various branches into one box and thus simplifies access to connections and for fusing.
Distribution boxes are classed by their number of branches into two types, the 8-way and the I2-Way box, the difference in construction being mainly that of length.
The boxes have usually been installed at the end of a main only, but a through run is now practiced, by casting a boss on both ends.
The 8-way box is shown in Fig. 41.
The end boss (a boss in each end in latest designs) is tapped for one-inch conduit to carry in a maximum wire size of 30,000 cm. conductor (usually twin conductors) for the main, the side taps-4 each side—are for Y2-inch conduit for a maximum wire size of 4107 cm. twin conductor. The box is secured, if necessary, through four screw wells, in masses, in the corners. In the bottom of the box are four tapped bosses for the screws securing the interior fitting.
The cover is secured with twelve screws and is cut, for an Opening by two plates, hinged together and held to the cover by screws; the plates are lined with cloth-insertion sheet-rubber Packing, cemented on.
The interior fitting consists of a slate panel, on which are installed two copper bus bars of 30,000 cm. cross- section, leading to the end boss of the box, and ending in two contact screws Which secure the binding plates for the wires of the main: Extending towards the sides of the box, and secured to the bus bars, are eight copper connectors for feeding the branches; on the outer edge of the slate base, across the fuse gap, are other copper connectors with contact screws for the branch wires; both sets of connectors are fitted with clips and guards identical With those used in the branch junction boxes. The fuse gaps are bridged with the standard glass-tube fuses.
In assembling, an oil-filled, hard wood block is placed between the slate base and the bottom bosses of the block.
The type of box has the disadvantage that the branch taps are so close together that the conduit must be bent to accommodate the individual switch boxes which are grouped near the distribution box.
Switches
There are five types of switches (and one special switch) of which all except the 5-ampere are double-pole; their office is to make or break, cut in or cut out, the electrical supply of the lines which they control.
100-Ampere Double-Pole Switch.—This heavy switch is installed on feeder lines, on inter-connections between feeders and on search-light leads at the base of the projector, when the switch is not self-contained. The conduit type is shown in Fig. 42.
The box has a boss at each end only, capable of taking a conduit of 1 ½-inch pipe size. Four screw-well masses are provided at the corners.
In the bottom of the box are two bosses for securing the interior fitting.
The cover is pierced at the center for the tube forming the entrance for the switch handle shown; the entrance is closed at other times by the standard screw cap.
The interior fitting has a connector at each corner, one end of which is fitted with a binding strap for the entering wires; the other end is bent in towards the center and ends in a tongue which can be caught between the clip plates on the switch barrel, embodying the general principle of a knife switch at each tongue. Two tongues, diagonally opposite, are bent down into the recess of the block to separate the clip plates of opposite polarity by one-half inch.
PHOTOGRAPH (page 120)
FIG. 42 – 100 ampere switch, conduit
The switch barrel assembly consists of a central steel stem fitting in a square base, the base being secured on the bottom of the block by a nut. On the shoulder of the square base is slipped a hard rubber insulating washer, above which are the lower sets of clip plates, separated from each other by a copper washer 1/8- inch thick. Above this pair of clip plates is a second set of same construction separated from the former by a hard rubber washer ¼ inch thick. A hard-rubber washer at the top and a brass follower, secured by four through screws, completes the assembly.
The switch stem is insulated from current carrying parts by hard-rubber bushings.
The switch is made quick-break, to shorten the time interval of arcing, by two steel springs, bearing against brass plates, sunk in deep slots in the block.
The clip plates cross the fitting diagonally, and hence the polarity of corresponding wires at the two ends of the box will be different, or the polarity will be "crossed" in the box.
The switch is turned by a through pin on the switch stern which fits a corresponding score on the base of the hollow stem switch handle.
50-Ampere Switch, Double-Pole, Single Throw—This large switch replaces the too-ampere switch when a current of about 50 amperes is to be the maximum to be carried on the main. The conduit type is shown in Fig. 43.
The box has four screw well masses at the corners and end bosses. The cover is cut in the center for the switch handle and closed with the standard cap.
The interior fitting is a modification of that for the too-ampere switch and crosses the polarity. Two of the four corner connectors are short and are bent down into the block recess, with a tongue to take between the clip plates at this end, and binding
PHOTOGRAPH (page 121)
FIG. 43 – ampere switch, conduit
straps at the other. Two connectors are long with binding straps but have, instead of tongues, a straight copper connector ending in a punched washer and which forms part of the switch barrel assembly.
The stem of the switch barrel is similar to that of the too ampere switch, the square base and steel spring, which make the quick-break, being smaller. On the shoulder of the square base is an insulating hard-rubber ring, above which is placed One of the lower clip plates, next come the washer ends of the long connectors, then the second of the lower clip plates; each clip Plate is made in two leaves to reduce stiffness. The upper clip Plates are similar to the lower and are separated from them by a porcelain washer Yi inch thick. A hard-rubber washer and a copper follower completes the assembly. The switch handle and through pin are the same as for the 100-ampere.
The punchings in the washer ends of the long connections provide collars in which the barrel turns and which secure it in place. Stops on these washers limit the throw of the clip plates.
50-Ampere Switch, Double-Pole, Double-Throw—This switch, commonly known as the Transfer Switch, is a modification of the 50-ampere, single-throw, switch. It is installed to connect to a main carrying about 50-amperes when the main is to be fed from either the lighting or battle circuits (such as a main for signals, running lights, etc.) and is to be connected to both. The conduit type is shown in Fig. 44.
The box has a boss on one side but is otherwise similar to that for the 50-ampere, single-throw.
There are four corner connectors in the interior fitting which are similar to the short .connectors of the 50-ampere, single
PHOTOGRAPH (page 122)
FIG. 44 – 50 –ampere transfer switch, conduit
throw, switch. The two sets of two-leaf clip plates and the switch barrel are assembled similarly to those of the 50-ampere, single-throw, except that, instead of the long connectors, there are two side connectors with binding straps which have their end washer rings assembled in similarly to those of the long connectors; the washer rings have no stops and the clip plates can be swung completely around. The polarity is crossed in the connections.
Special Switch, Double-pole, Double-throw—This large switch, shown in Fig. 45, is not carried in stock. It is a transfer switch designed to carry the heavy load of 800 amperes for use in transferring power loads for the 12-inch or 13-inch turrets from the circuits of the forward to the after dynamo room and vice versa; the small number used in any installation are made up as required.
The box is a built-up box of 1/8-inch galvanized sheet iron flanged at the lower end for securing to a bottom plate of iron 18¾ inches x 14 1/8- inches x 5/16 inches thick, and provided with a hinged cover and a hasp for a padlock. The side of the box in the wake of the terminals has openings sufficiently large to admit the large wires.
All parts of the switch proper are of hard drawn copper; pins are of phosphor bronze; and screws and washers of brass.
Overall dimensions of the box are 18 ¾ inches x 14¼ inches x 11 inches (high).
The poles of the switch are made up of two blades each, 2 inches by 7 3/8- inches by 7/32 inch, secured to hinge posts, and to blade caps which are secured to a hard rubber yoke. On either side of the yoke is a handle at right angles to the blade of the switch. There are two clips per blade, let in and brazed to
PHOTOGRAPH (page 123)
FIG. 45 – 800-ampere special (transfer) switch, conduit
foot-pieces; there is a separating piece between the clips, which ads as a stop for the blades. The foot pieces are mounted on a slate base and secured from the under side with two brass machine screws.
The slate base is secured through two strips of sheet rubber packing to two wrought-iron straps; these straps are bent into an inverted U-shape, and secured to the bottom plate of the box by hexagonal brass tap bolts.
The foot-pieces for one pole of the switch are slotted to a depth of 1 3/16 inches to receive the shanks of one set of terminals; the foot-pieces for the other pole of the switch are connected to busses located below the slate base. These busses are made in two pieces, separated from the slate base and from each other, and are secured to the studs by hexagonal nuts. The shanks of another set of terminals at the other end of the busses act as separating pieces.
The terminals are located on one side of the box; the large end terminals are for the bus wires from either distribution room, and the four small center terminals are for the circuit leads around the turret.
25-Ampere Switch, Double-pole—This snap switch is a line switch for mains or leads not expected to carry more than 25 amperes. The conduit type is shown in Fig. 46.
Four screw well masses are located in the box ends inside of the holes for the cover screws. There is but one boss at each end.
The cover is held by four screws and is cut for the entrance of the switch handle, the entrance being closed by a standard cap. The entrance is off the box center.
PHOTOGRAPH (page 124)
FIG. 46 – 25-ampere switch, conduit
The switch stem of the interior fitting extends up through the block and switch barrel; on its lower end is riveted a brass plate carrying diametrically opposite pins on which small brass rollers journal; the rollers run on a brass ratchet in the bottom of the porcelain block, fitted over a ratchet in the porcelain corresponding in breaks to the breaks on the porcelain ratchet of the switch barrel. The central part of the stem is flattened to take the rectangular section of the interior of 'the switch barrel and drive it.
The switch barrel is a porcelain cylinder, part of whose boring is rectangular; the cylinder surface is molded to form four ratchet teeth, two of which, diametrically opposite, are surfaced with copper sheet held by solder, the other two teeth are blank porcelain.
The line connectors are two long and two short, ending in binding straps. The long connectors are on a raised part of the block and end in a vertical flange to which is riveted a snap finger bent round to bear on the curve of the ratchet teeth of the switch barrel. The short connectors are similarly fitted but are flanged down into a recess of the block to take the snap finger.
As the switch is snapped from a ratchet tooth, one long connector and one short connector on the same side of the block are either connected through the copper plates on the switch barrel or are insulated from each other on the blank teeth. The polarity of the line is not crossed in the switch.
5-Ampere Switch, Single-pole—This snap switch is the one generally inserted in lines branched to outlets for controlling the individual outlet, provided no greater current than 5 amperes is
PHOTOGRAPH (page 125)
FIG. 47 – 5-ampere switch, conduit
to flow. The conduit type is shown in Fig. 47. (When the switch is to be at the end of a pipe, the type of box shell is similar to that shown in Fig. 49.)
There are but two screw wells located at the end which is fitted for the two bosses. The cover is held by four screws. The switch handle remains permanently with each box, and, to prevent water from entering, a rubber gasket and stuffing box are fitted to the cover, and assembled together by a standard cap, drilled to take the switch stem.
The switch being single-pole, the connectors are connected together by a copper plate. The connectors are of brass; one leads to the copper plate and thence towards the switch barrel, where a spring finger similar to one of the fingers for the 25- ampere switch, is secured by a screw; the other connector is short and secures a similar finger.
The switch barrel, is of porcelain, similar to but shorter than that for the 25-ampere switch. Over the barrel is slipped a
copper stamping which fits two diametrically opposite teeth- of the barrel ratchet, to make and break connection with the connector fingers. The brass switch stem has rollers and ratchets beneath the block identical with those of the 25-ampere switch.
The switch barrel is held down by a steel spring which shoulders against a brass sleeve on the stem above the spring. Above the sleeve is a pin by which the thumb nut drives. The thumb nut is a casting having a small ratchet at its bottom face, and a spring in the core which takes against the head of the screw securing the thumb nut to the stem. This arrangement prevents turning the switch in the wrong direction and thereby bending the fingers; the thumb nut will spring up and back if the ratchet is turned left-handedly, and only the handle will turn.
PHOTOGRAPH (page 126)
FIG. 48 – 25-ampere switch and receptacle, conduit
Receptacles
The type is designed for the purpose of providing an outlet into which the wiring of movable fixtures can be plugged, for current supply, by means of one of the standard attachment plugs.
25-Ampere, Switch and Receptacle, Double-pole—The conduit type is shown in Fig. 48.
The box has four screw wells, and with one boss at the end.
The cover is pierced for three entrances, two near the ends for the two 25-ampere attachment plugs, and one near the center for the switch handle.
The block is the same as that for the 25-ampere switch. The difference for the remainder of the interior fitting and that of the 25-ampere switch is that the long connectors have a contact clip for the attachment plug instead of a binding strap. This contact clip is of phosphor bronze; the sides are bent slightly out of rectangle and their upper ends are turned in to give a spring action in holding the plug.
5-Ampere Switch and Receptacle—The conduit type is shown in Fig. 49.
The box is the same as for the 5-ampere switch excepting that the cover has an additional aperture for inserting the 5-ampere attachment plug. (See description of 25-ampere attachment plug
PHOTOGRAPH (page 127)
FIG. 49 -5-ampere switch and receptacle, conduit
and 5-ampere attachment plug for the important electrical difference in construction. This difference has been sometimes overlooked in fitting double conductor, plain, for fixtures.)
The block and switch are the same as for the 5-ampere switch; the difference for the remainder of the interior fitting and that of the 25-ampere switch is that the long connectors are not con-
PHOTOGRAPH (page 127)
FIG. 50 – 5-ampere receptacle, conduit
nected together by a copper plate but end in one vertical phosphor bronze piece like one of the 25-ampere switch-and-receptacle contact clips. The 5-ampere attachment plug requires a gap and not a connection between the clips.
5-Ampere Receptacle—The receptacle is for use where the switch combination is not required. The conduit type is shown in Fig. 50. The box is the same as for that for the 5-ampere switch and receptacle except that the box cover has but one aperture, which is fitted with a cap. The switch parts of the 5- ampere switch and receptacle are omitted in the interior fitting; the straight brass connectors are connected through the box to the same type of contact clips as in the 5-ampere switch and receptacle; the other ends of the long connectors end in a contact screw.
The 5-Ampere Double Receptacle—The conduit type is shown in Fig. 51, and is, in effect, two 5-ampere receptacles combined. The difference between this receptacle and the 5- ampere receptacle is that there is a set of clips at each end of the interior fitting instead of at one end only, and the box cover is cut with two apertures, for the insertion of two 5-ampere attachment plugs, each aperture being provided with a standard cap.
PHOTOGRAPH (page 128)
FIG. 51 FIG. 52
FIG. 51 - 5-ampere double receptacle, conduit
FIG. 52 - 5-ampere switch, with hood, conduit
The double receptacle is installed in staterooms for the two outlets required for one fan and one desk light, and takes the place of non-watertight receptacles, key and keyless.
5-Ampere Switch, Single-pole, with Hood.
25-Ampere Double-pole Switch and Receptacle, with Hood.
5-Ampere Switch and Receptacle, with Hood.
The distinction between these three types and the types which have been previously explained (without the hood) is merely in the shape of the box shell, of which a type is shown in Fig. 52.
The top of this box is curved into a semi-circle and is flanged out over the top to cover the face of the appliance and protect the handle from loose gear about decks, or when the appliance is likely to be stepped on about hatches, or from the weather on uncovered decks. The box cover is cut to fit the extended and rounded shape of the top of the box shell, otherwise it is similar to those for the unhooded appliances.
Box Types for Interior Communication Circuits
Connection Boxes—Connection boxes are of four sizes, known as 20-wire, 40-wire, 60-wire, and 70-wire boxes. They afford a convenient means of branching out the interior communication leads, from the cable or from main wire leads, to the different locations in which a part of the wires are to be distributed or
PHOTOGRAPH (page 129)
FIG. 53 – Connection box, interior communication
are to connect to interior communication apparatus, as bells, annunciators, etc. The box and fittings are shown in Fig. 53.
The box is of cast bronze composition and is secured in place through four screw wells. In the bottom are cast four long bosses, on which rest the interior fitting carrying- the terminals.
The cover is plain and is water tighted by a cloth insertion sheet-rubber packing, which only covers a portion of the inside edge of the box, the packing being secured to the cover by tap screws and by the screws which hold the cover to the box shell. There are no pipe bosses on the outside of the box, but on the inside of each box wall are bosses which are to be tapped to take the ends of the conduit.
The interior fitting is built up of micanite into an open square and drilled at the corners to be secured by screws to the bosses; the corners are cut away to fit inside of the screw well masses. On the four sides of the micanite are secured the plates to which the wire terminals are held by screws; the terminals are copper stampings bent into tubular shape at the ends that the wire end may be conveniently entered and soldered
PHOTOGRAPH (page 130)
FIG. 54 – Action cut-out switch
There are five plates on each side of the twenty-wire box, ten on each side of the forty-wire box, and fifteen on each side of the sixty-wire box, but the total number of connections can be increased by securing other terminals under the same screws, as in the case of several common returns. Necessary room is afforded in the bottom of the box for disposing of the slack of the conductors and the terminals are made sufficiently long to be bent down for convenience and as required. The number of the particular wire lead is stamped into the terminal by a die.
In the forty-wire box there are three bosses inside of each box wall, admitting of twelve conduits or box tubes, if required.
Cut-out Switch—This switch (known as the Action Cut-out), is shown in Fig. 54; the size shown in the figure is for 22 wires. It combines in one appliance the means of cutting off a number of lines of interior communication which are to be used in action (and behind armor or other protection) from other parts of the same lines which -are not required in action, and which latter from exposure to injury might occasion grounds or short circuits in the system.
The various uses of the switch are referred to under Installation.
The box is a composition casting. Bosses for the attachment of the stuffing tubes or conduits are located externally on the sides, to be tapped as required. Bosses are also cast internally on the sides, to be drilled to take the screws for securing the box in position when conduit is not installed.
Bosses are raised on the inner bottom and drilled and tapped to take the screws for holding the base.
The upper edges are tapped to take the cover screws, the corners being filleted and the bosses swelled out where the screws come between the corners.
The cover is of thick sheet brass with a central rectangular hole for ready access to the fitting.
Two lugs on the left hand edge form parts of hinges. On the right-hand side two inclined surfaces, called wedges, are cast which form part of the ready locking device for the cap.
A cloth insertion sheet-rubber packing is inserted between the surface of the cap and the cover to watertight the appliance.
The cap is clamped by two handles which force the cap against the packing by pressure on the wedges in the same way as the dogs on a watertight door. The heavy extension of the handle Prevents any loosening by jar.
On the inner surface of the bottom of the box is placed a micanite sheet to insulate the fitting and its screws from contact with the metal.
The interior fitting consists of a rectangular slate base on which are mounted a number of knife blade switches, single throw, the blades being connected in sections to two or more common switch yokes. To each of these yokes is fastened an open switch handle which admits of the simultaneous opening or closing of all of its contacts, the cap being opened for the purpose.
Terminals, to which the conductors are soldered, are fitted to each switch terminal, space being allowed for stamping the individual wire numbers.
Allowance of space is made between either side of the switches and the sides of the box for the leading in of the wires.
Transfer Switch (Interior Communication)—This switch is ordinarily of similar construction to the cut-out switch. The main difference is that the switches are double-throw to permit alternative locations, such as a chart house and conning tower, to be connected to the same lines. Its convenience resides in reducing the number of cut-out switches which would be otherwise necessitated and preventing two being on at one time.
The Watertight Box and Pulling Sleeve - These two appliances have no interior fitting and are not strictly boxes.
Watertight Box—This box is installed on conduit lines near a deck or bulkhead to stop the flow of water which may have entered the conduit from any cause, such as covers or caps being left off of boxes, or from rupture of the conduit in action in a compartment which has been flooded; or from condensation.
There are two similar types shown in Fig. 69, one of which is employed when the appliance can be located close to the bulkhead. The second type is for use when the appliance must be located farther away from the bulkhead from interference of structure or apparatus; it is similar to the former type, differing in the length of stuffing tube to be employed.
PHOTOGRAPH (page 132) (along left margin of paper)
FIG. 55 – Pulling sleeve
The box is merely a casting, bottom hemi-cylindrical, with cover for access. Within the box one end of the conduit is water tighted by gland and gasket in the usual way; the box surrounds the end and preserves a continuity of the conduit, and the removal of the cover permits access to the gland and gasket for setting up. The gasket set up, the conduit is protected from communication of water between compartments.
Pulling Sleeve—This appliance is shown in section in Fig. 55. It satisfactorily replaces, and is much lighter than, the former pulling box, and also obviates cutting a long length of wire.
Over the conduit shown is placed a brass tube whose ends are threaded outside, and are beaded inside, to take a rubber gasket, which is set up by a gland against a brass washer. The sleeve is a convenient device for access to the wiring, the ends of the conduit being separated a good distance as shown; the pressure of
PHOTOGRAPH (page 133)
FIG. 56 – Terminal box for staterooms
the gasket retains the sleeve in place; when drawing wire the gland is slacked and the sleeve slipped along the conduit out of the way.
The different particulars for different size sleeves are tabulated as follows:
CHART (above, form page 133)
Terminal Box
There are several sizes of this appliance which are used merely as a terminal base into which the wiring can be led and to which some forms of appliance can be secured. In general they are similar to Fig. 56, but when several are to be assembled at the same place the box is made to include all in the same casting.
The type shown is that which has been used in staterooms for mounting push buttons for the bell circuits, and the switch for the lighting circuit. The conduits enter in an upper surface not shown in the figure.
Non-watertight Appliances
Appliances of the non-watertight types are of commercial varieties, and replace the more expensive watertight types in locations outside of the watertight system of the ship, especially in those locations which are occupied as quarters, offices, etc. Non-watertight appliances should never be used in. locations which will be washed down with hose.
PHOTOGRAPH (page 134)
FIG. 57 – 5-ampere FIG. 58 – N.W.T.
Switch, N. W. T. key receptacle
5-Ampere Switch—The switch is the single-pole, snap switch shown in Fig. 57.
The circular porcelain base has two raised bosses to which are held small brass connectors by screws through the base; the connectors are fitted with contact screws to which the leading wires can be directly connected, or they can be led through holes in the base. The copper fingers are riveted to the connectors and make contact on a switch barrel similar to the method of the 5-ampere watertight switch. The barrel contacts are held by a solder joint, run into a recess in two opposite ratchet teeth, and are connected together through the barrel. The switch stem is flared under the base and held by a slotted brass washer; it is secured to the barrel by a coiled spring, one end of which goes over a pin on the stem and the other takes in the interior recess of the barrel. The switch handle screws on and is held by a set screw.
The cover is of spun brass, lined with asbestos, dome-shaped, and finished in bronze; it is held in place by the switch handle and is kept from turning by a notch on the lower edge which fits over a lug in the porcelain base.
The switch is commercially rated at 10 amperes.
The direction of turning is to the right and no device except the resistance of the switch fingers prevents turning in the wrong direction.
The appliance is secured through screw holes in the base; when installed in connection with conduit work it is attached to a terminal box similar to that shown in Fig. 56 and the wires are led through the two holes in the base.
10-Ampere Switch—The essential feature is that the switch is double-pole; this is important and has been much overlooked, causing errors in installation and contract deliveries. The base is the same as for the 5-ampere, except that the bosses are higher and there are four holes for the wires instead of two. Similar short connectors are used with the same construction of finger; four fingers are used, two in each pole, one of each pair being secured to the upper surface of the base and one to the boss. The barrel is similar to that of the 25-ampere watertight switch, the contact plates being secured by solder as in the non-watertight 5-ampere switch, and connected through the barrel. The stem construction, method of holding to the base, handle and cover fastening are the same as for the 5-ampere non-watertight, but the cover is higher to accommodate the extra height for the fingers and is lined with asbestos.
The switch turns to the right and has no device except the resistance of the switch fingers to prevent turning in the wrong direction. The appliance is secured through two screw holes in the base; When installed in connection with conduit work it is attached to a terminal box similar to that shown in Fig. 56 and the wires are led through the four holes in the base.
RECEPTACLES
Key Receptacles—The appliance is shown in Fig. 58.
The porcelain has a flat circular base with a central porcelain column. To the column is first screwed a D-shaped piece of brass in whose upright ends the key spindle journals. At the key end this stamping is branched for a contact screw for one fuse; at the opposite end the journal is deepened to allow for the spring action. The key stem has a through pin or plate inside each side of the D-shaped piece to keep those sides in place, and on the opposite end from the handle and inside the D is a rectangular piece of brass which, when vertical, electrically connects the shell of the socket with the switch stem; the piece of brass works against a phosphor bronze spring plate to give a snap action.
The other electrical terminal is a tongue of brass ending in a plate against which the center of the lamp base, or attachment plug, rests, and to which the center connects electrically. The tongue is bent down and screwed to the column and is tapped in for the second fuse. The socket shell is cut away, where the tongue passes through, to give large room to prevent short circuit.
The socket shell is of spun brass, threaded to take the Edison base of the lamp or attachment plug; it is inwardly flanged at the bottom and held to the column by two screws.
The tongue is often bent down when a lamp or plug is screwed in hard and, to prevent short circuiting, a disc of mica is laid under the tongue.
The wire contacts are two brass plates held by screws to the flat base. Each contact has two contact screws, one for the wire lead, the other for a piece of fuse wire to fuse the gap between the wire contact and the contact screw of the tongue in one pole, and that between the wire contact and the contact of the D-shaped journal of the switch stem in the other pole. The fuse is no longer used in naval work; the gap is bridged with a metal connector.
The cover is of spun brass with an aperture large enough to fit over the switch handle. A broad notch at the bottom, and directly below the handle aperture, fits over a corresponding elevation on the base and prevents the cover from turning. The cover is held in place by an insulating ring of hard rubber, whose internal thread fits the thread of the socket. The cover is lined with asbestos.
The receptacle is secured by two screws; when installed in connection with conduit it is attached to a terminal box, similar to that shown in Fig. 56, the difference being in the shape and arrangement of parts.
Keyless Receptacle—This appliance, shown in Fig. 59, differs mainly from the key receptacle in the omission of the key construction; the column is not so high and has a one-sixteenth inch raised projection against which a broad tongue is held in the bend on the side by the fuse screw; the socket shell is held by two screws, and by a horseshoe-shaped connector which has a tongue and contact screw for the fuse in the other pole; the cover is lower and has no device to prevent turning. The wire contacts, fusing, and other details are similar to those of the key receptacle.
The keyless receptacle is installed when the local use of a key is not necessary.
The double receptacle (Fig. 51) now replaces both the key and keyless receptacles.
PHOTOGRAPH (page 137)
FIG. 59 – N. W. T. FIG. 60 – Standard
Keyless receptacle key socket
LAMP SOCKETS
These appliances are the receptacles for securing and supplying the incandescent lamps in the various types of fixtures and instruments.
Key Socket (Fig. 60)—There are two parts, an interior fitting and a shell.
The function of the interior fitting corresponds in most details with the column parts of the N. W. T. key receptacle. It is not fused and there are no lower contacts as in the key receptacle; the key construction is the same in both. A commercial Spun socket shell is secured to the porcelain by two screws and is cut off at the height of two threads, the remaining threads being replaced by a coiled spring of No.11 phosphor bronze wire, of seven turns, of which three-quarters of a turn are soldered in the thread of the spun shell and 6¼ turns are free in the spring; the outer end of the spring is turned back in a loop, to be pressed back and loosen the spring when unscrewing the lamp. The threads of the lamp base run in on the spring as on the thread of the socket shell of the key receptacle; the object of the spring device is to protect the lamp from loosening or breaking from the effect of shock or vibration.
The shell is in two parts, a top and a base. The top is of spun brass; it has one slot at the bottom to slip over the key stem, and two slots to slip over the retaining screws which hold it to the base by the pressure of the screw heads; the ends of these screws enter a recess in the porcelain and hold the interior fitting in place. The upper part of the base is of spun brass, reinforced inside by two spring straps, double the thickness of the brass spinning, to afford a bearing for the screws which assemble the side.
PHOTOGRAPHS (page 138)
FIG. 61 – Standard FIG. 62 – Type A
Keyless socket socket
The bottom of the base is a casting tapped for the pipe thread of the pipe of the fixture to which it is to be attached, a slotted head set screw preventing turning.
The wiring is led through the pipe and base to attach to the contact screws of the interior fitting. The shell is finished in dark bronze in consonance with the finish of the fixture with which the socket is to be assembled.
The side of the shell is insulated from the coiled spring by a ring of hard rubber, bent to shape and slipped in at the top between the shell and spring.
Keyless Socket—The porcelain block for the interior fitting of the keyless socket (Fig. 61) differs from that of the key socket in the omission of key parts. The coiled spring and tongue connection are the same. As in the keyless receptacle, a horseshoe-shaped piece of brass is assembled with the inside flange of the bottom of the spun socket (to which the contact for one pole is attached). The side of the shell omits the slot for the key, but is otherwise the same as for the key socket and assembled in the same way. The shell is finished in dark bronze.
Type A Socket, or Porcelain Base Receptacle—This type of socket shown in Fig. 62, is now replacing the key and keyless sockets in many constructions (especially fixtures) as it is cheaper, has better insulation and is more readily wired up; the difficulty of leading in through the bottom of the base of the other two sockets, and attendant delay and cost is also eliminated. It has no cover or shell and consists essentially of the mountings of a keyless socket on a special porcelain base. The efficiency of circuit insulation in conduit installations is largely due to the use of this socket.
PHOTOGRAPH (page 139)
FIG. 63 – Candelabra base, or FIG. 64 – Push button, N. W. T.
Instrument lamp socket
The base is secured by a through No. 8 machine screw on one side, and on the other by a machine screw of the same size, Which sets against a shoulder in a slot, permitting the taking up of a variation of one-quarter of an inch in centers.
A deep groove for the entering .wires runs across the bottom of the base. The porcelain is so struck on the top of the base as to form a shoulder for leading the wires to contacts whose center line is 90 degrees from that of the bottom groove and in the same vertical plane as the securing screws. All screw holes for screws securing the mountings are countersunk and filled with a water-excluding material.
Instrument Lamp Socket—This socket (Fig. 63) takes the 5-candle power instrument lamp base. The porcelain is held by screws at diagonally opposite corners.
The copper spinning and spring are constructed like the similar parts of larger sockets. One connector is soldered to the copper Spinning; the other dips down into a recess of the porcelain, and extends up vertically into the socket center, where it is secured by a copper screw over an insulating disc of mica. The same screw acts as a wire contact and for securing the connector.
Push buttons are a simple variety of through-connection or switch for low-voltage lines, such as for bells and buzzers.
There are two types of push buttons: A flat type, known as Watertight and Non-watertight Push Buttons, to be installed against surfaces on lines of bell wiring; a pear-shaped type, known as Single, Double, and Triple Pear Push Buttons, designed to be attached to loose bell cords, to hang over tables, beside desks, etc.
Non-watertight Push Button - The appliance, shown in Fig. 64, is a brass casting and consists of four parts, a base, a cover, an interior fitting, and a push.
The base casting is hollowed out in the center for lightness and for a direct lead for the wiring; it has a cast collar, threaded on the outside, to which the cover screws. In a recess of the collar is placed the interior fitting. The cover is a casting, threaded on its inner, lower edge to take on the threaded collar of the base, and perforated at the top for the push.
The interior fitting is a disc of hard rubber, perforated for two screws which hold the complete push button in place, and two smaller holes, through which the wires are led to the contact springs. There are two German silver contact springs; one, laid flat, and half-moon in shape to bring the inner end to the center of the hard rubber disc and at the same time clear the other connector, is secured to the disc by a screw, a second screw with small brass washer forming the wire contact; the second connector is bent into a spiral and is secured to the disc by a screw, the wire contact being the same as for the first connector, this connector is sprung off the disc to give a clearance of about 1/8- inch between its inner end and that of the first connector. The inner ends of each connector are fitted with a small pin rivet of platinum to decrease the effect of sparking, and insure a clean, bright contact.
A notch in the side of the hard rubber fits a lug in the base and secures the fitting against turning.
The push is a piece of hard rubber about 7/16 inch in diameter at the top, with a small flange at the bottom about 1/8- inch larger in diameter, which presses on the spiral connector inside the button, and brings the platinum points of the connectors into contact. In conduit wiring the button is attached to a terminal box similar to Fig. 56.
Watertight Push Button—The watertight push button is similar in construction to the non-watertight, but the base is made solid excepting for a perforation on one side about ½ inch in diameter, in which fits a hard rubber plug with two holes for the leading-in wires.
The construction of the interior fitting is similar to that for the non-watertight button. The cover is the same excepting, first, at the top is a collar with an outside thread, to which is fitted an inside-threaded ring holding in place a lace leather disc
PHOTOGRAPH (page 141)
FIG. 65 – Parts of single pear push button
Which covers the push of the button and watertights the top; second, a watertight packing is placed under the cover. The lace leather is more serviceable than rubber, preserving its flexibility when exposed to salt water and not softening when acted upon by oil. In conduit wiring the button is attached to a terminal box similar to Fig. 56.
Single Pear Push Button—The single type is installed when but one station is to be called. Fig. 65 shows the type of appliance. It consists of hard rubber turned in two sections, a base and a cover; the cover is threaded to take an inside thread in the recess of the base.
The lower part of the base is drilled to take a double bell cord, and holes are drilled through to the base recess through which the bell cord can be drawn (after stripping the silk braid) and the wires branched out to the two contact screws, with washers, within. In the center of the recess is bored a hole about ¼ inch deep, in which is set a spring which embraces the pin of the contact disc.
The contact disc is made of German silver, and has a small central pin to take the spring. This contact disc when pushed down on the two contact screws to which the wires are fastened completes the circuit between the two wires of the bell cord. A nickeled brass push is inserted through the hole in the cover to take on the contact plate; the push is kept in place by the cover; the contact disc is kept off the contact screws by the spring.
Double Pear Push Button—This type is installed when two stations are to be called from one appliance.
The double pear push button is similar in appearance to the single pear push though slightly larger and has two pushes, one at the end and one on the side. The base is bored out leaving a wall thickness of about ¼ inch which is inside-threaded at the top to take the thread of the cover. Inside the base fits a hard rubber plug carrying the contact screws. The plug is planed off on one side for the connections for the side push, and holes are drilled through for the wires (without silk braid) of the triple bell cord. The battery wire contact screws for the top and side push are connected together by a brass strip.
The two contact discs, springs, and pushes are the same as for the single pear.
Triple Pear Push Buttons—This type admits of calling three stations from one appliance.
The triple pear push is of the same size as the double pear and has two side pushes in addition to the end push.
The only essential difference is in the plug which is planed away on two sides for two side constructions similar to the side construction of the double pear push button.
The three-battery wire-contact screws are connected together by a strip of brass.
There being no standard bell cord, quadruple, the conductor is laid up by hand from single silk conductors.
Ceiling Button—This is a small circular porcelain appliance used as a finish at the upper ends of bell cords, and is secured by two screws. The base of the ceiling button is hollowed out, and scored on opposite sides, for the lead of the bell wires, which are to be connected to the bell cord. In conduit wiring it is replaced by a hard rubber bush in the cover of a terminal box similar to that used for the non-watertight push button.
Auxiliary Wiring Appliances
Gaskets—The term gasket is generally restricted in electrical installations to the eight types of soft rubber appliances for watertighting, of the shape of two truncated cones of unequal heights Joined base to base, and resembling rubber corks; these are perforated to fit over the wires or conduits, and are set up by a gland and washer. Gaskets are generally molded from a rubber composition which is required to be as follows:
PHOTOGRAPHS (page 143)
FIG. 66 – Types of gaskets
To be made of a vulcanized rubber compound which shall contain nothing but pure Para rubber gum, of the best grade, mixed with dry mineral matter and sulphur only. The compound to contain at least 60 per cent, by weight, of rubber gum, and the weight of sulphur not to be less than 4½ per cent nor more than 5½ per cent of the weight of the rubber gum in the compound. This sulphur shall all be combined with the rubber so that there shall not be more than two-tenths of one per cent of free sulphur in the compound.
After vulcanization and manufacture into gaskets, the character of the compound to be such that when a test piece having a section of about 0.03 square inch is placed in jaws 2 inches apart, or as nearly 2 inches as may be practicable, and the jaws separated at the rate of 3 inches per minute, subjecting the rubber to a tensile test, to be capable of being stretched to five times its original length, without rupture and not break under a tensile stress of less than 750 pounds per square inch.
When subjected to a tensile stress of 600 pounds per square inch continuously for ten minutes the compound to be of such a character as to return to within 15 per cent of its original length at the end of ten minutes after being released.
The specific gravity of the compound not to be less than 1.3.
The several types of gaskets are designated by a type letter in accordance with the outside dimensions of the gasket (Fig. 66). Varieties of the same type are designated by a number, generally separated from the title letter by a dash, which conveniently designates the diameter of the perforation in the gasket in thirty seconds of an inch; for instance, A-14, B-20, D-13, indicate a gasket of A, B, or D, sizes in which the diameter of the hole is 14, 20, and 13 thirty-seconds of an inch, respectively.
If the type letter is a single letter, as A-14, it indicates that there is but one perforation in the gasket; if there are two perforations for the same size the gasket is called AA-4, etc.
When a gasket is represented as A-o, B-o, etc., it indicates that the gasket has no perforation and is solid; such a gasket is used for plugging up or blanking off, but the occasion is rare except with appliances for molding.
Gaskets which are designated by two numbers, as A-24-13, are for packing twin conductor, and have a single perforation with semicircular ends of which the first number, 24 in the example above, is the length of the perforation and is one thirty-second of an inch larger than the major axis of the twin wire; the second number, 13 in the example above, is the width of the perforation and is one thirty-second of an inch smaller than the minor axis of the twin wire.
Attachment Plugs
Attachment plugs are appliances which are used on the ends of wire for plugging into receptacles, switch and receptacles and the like, and form the electrical connections to the permanent ship wiring of the particular fixture or apparatus to which they are wired.
5-Ampere Watertight Attachment Plugs—This appliance, shown in Figs. 50 and 51, consists, first, of a hard rubber plug having a threaded collar at the top by which it secures in the assembly. On the sides of the plug are two copper connecting plates held by two brass screws, each having a contact screw under which one of the wires (usually from a double conductor, plain) are secured. The plates are insulated from each other by the substance of the plug, and the plug is therefore double pole when inserted in the clips of the receptacle.
The brass parts consist of a collar turning in a ring which is inside-threaded to take the tube of the box appliance, the recess being packed with a ring washer of sheet rubber packing to prevent access of water. The collar is knurled on the outside. The upper part of the brass tubing, into which the hard rubber Plug is screwed, is reamed for packing with a D-I3 gasket, and the gasket is held in place by a gland, working against a brass washer. The two wires of the double conductor, plain, are bared to the vulcanized rubber layer, and led down through holes in the hard rubber plug to connect to the contact screws.
This appliance has the great disadvantage that the screw collar at the top of the hard rubber plug has insufficient strength and is easily broken. A newer type of this appliance uses lignum vitae boiled in paraffin instead of hard rubber. This type of plug is watertighted better at the leading-in wires than the type explained above; the breakage proves to be lessened only to a small degree.
25-Ampere Watertight Attachment Plug—This type is to be inserted into a receptacle which is single pole instead of double Pole, the clips of the 25-ampere receptacle, or switch .and receptacle, being connected across by the plug contacts from one to the other. The plug differs from the 5-ampere plug in having the contact plates connected across the plug end, thus making it a single pole; the two leading-in wires attach to the contacts of either side.
Non-Watertight Attachment Plug—This plug is shown in Fig. 67. It consists of a piece of hard rubber, recessed at the top for a depth of half an inch, and having a central hole dropping from the recess for a distance of ¼ inch. A screw enters this smaller recess from the bottom and secures a brass connector which is bent up into the larger, recess and ends in a contact screw for one wire, the screw completing the connection. On the outside of the plug is threaded a brass spinning which is connected through by a soldered wire to a contact on the inside. From this contact a fuse wire connects to a similar contact, placed at a distance of about ½ inch on the inside circumference of the recess, to which the second wire for the connection is secured. The commercial attachment plug is therefore fused; this is not necessary, one contact is now omitted, for naval use, and the fuse gap bridged.
The upper part of the plug is threaded on the outside for a brass cap, finished in bronze, which holds a hard rubber disc, covering the inside recess of the plug. The hard rubber disc and the cap are perforated to admit the conductors.
The appliance is used on the ends of wiring (usually double conductor, silk) for fans, desk lights, etc., but is now being replaced by the 5-ampere watertight plug by reason of the installation of double receptacles instead of non-watertight appliances.
PHOTOGRAPH (page 146)
FIG. 67 – N.W.T. FIG. 68 – Cross-section of conduit tube
Attachment plug through a bulkhead
Stuffing Tubes
The requirements of watertighting the fitting of various parts of conduit lines has given rise to a line of stuffing tubes differing for the particulars for which they are applied.
Conduit Tube—The tube, shown in section in Fig. 68, is employed for watertighting conduit when run through decks or bulkheads. It is of drawn tubing and beveled inside the ends for the gasket; it is threaded for its whole outside length if the tube is to be short, otherwise an unthreaded portion is left in the central part of the tube and the ends are threaded for the necessary length for nut and gland; the length of the tube will differ with the thickness of the metal and wood through which it is to
CHART (page 147)
Conduit Stuffing Tubes
be run. On the thread run two hexagonal nuts which clamp the tube to the bulkhead or deck. The recess in the nuts is packed with lamp wick and red lead to prevent a flow of water between the nuts and the metal to which the tube is secured. The gaskets are set up by glands running on the outside threads. When conduit is run through armor a tube is not necessary, other methods of water-tighting being used.
Bulkhead Tube—The bulkhead tube is a conduit tube having but one end fitted for gland, washer, and gasket. The jam nuts have a score instead of a recess which is to be filled with red lead to watertight between the nut and the ship metal.
The bulkhead tube accomplishes the ordinary demands of installation, the conduit tube being for locations where the conduit must be packed on both sides; it is better to use the recessed nut of the conduit tube than the scored nut of the bulkhead tube as lamp wick and red lead make a better joint than red lead alone.
If the bulkhead tube is to be short it is outside-threaded for its whole length, otherwise an unthreaded section is left in the center. It will answer for a deck tube as well.
Box Tube—The box tube is a small, short bulkhead tube having no jam nuts, and, is used for stuffing wires entering fixtures, and similar uses which require a short tube only.
Watertight Box Tubes—The modifications of the conduit and bulkhead tubes for this use are illustrated in Fig. 69, showing the arrangement when the watertight box can be located near the bulkhead—the more advisable—and also when such arrangement is not practicable.
Terminal Tube—The terminal tube is worked on the end of a conduit line when necessary to watertight wiring which is to be run open to cleats, insulators, etc.
When the conduit is to end at a bulkhead the watertight box tube is used as a terminal tube, but modified as follows: The shank of the tube (the part threaded with a pipe thread) is threaded to the shoulder instead of only part way; this shank is made long enough to pass through the bulkhead, take a nut (with red-lead groove) on each side of the bulkhead, and take its half of the coupling joining it to the conduit. One of these nuts is set up tight against the shoulder of the tube; watertightness is secured by setting up on the nut on the other side of the bulkhead.
LINE DRAWINGS (page 149)
FIG. 69 – Watertight box tubes and watertight boxes
CHART (page 150)
BULKHEAD STUFFING TUBES AND BOX TUBES
TUBES FOR WATERTIGHT BOXES AND CONDUIT TERMINAL TUBES
CHART cont. (page 151)
The enlarged part of the tube may be shortened to a length equal to that of the gland, or made longer if more advantageous.
A recessed nut is preferable to one with read-lead groove.
When the conduit ends flying, as in a berthing space, a short bulkhead tube is used for packing the terminal, screwing into a coupling. In similar cases when it is not necessary to pack the terminal, the type of terminal known as the T. & B. Bush or outlet insulator is used; its advantage is that the smooth, rounded, exterior edges will not abrade or injure the naked wire like the sharper edge of conduit pipe, however carefully the conduit may be finished off. The type is of cast iron and is commercial.
Page 152
FIG. 70 – Hinged hangers
Hard-rubber Bushes — When wire or cable (without duct) is run through a bulkhead, etc., and watertightness is not necessary, such wire or cable is insulated at the bulkhead by bushes of hard rubber cut from hard-rubber tubing. To prevent the bushes from working out of place they are secured in as follows:
The tubing is cut about one inch longer than necessary for the aperture, and each end is softened in hot water. The bush is then put in place and a conical piece of metal placed in each end; the pieces of metal are connected by a through bolt and, as the nut is set up, the bush ends are flared, holding the bush securely in place when the ends have cooled and hardened. Straight bushes cut from tubing are used to bush all holes in beams, etc., through which wires are led in molding work.
Conduit Hangers —Three types are shown in Fig. 70. A is the type for angle irons or against a surface having no offset; B is the type for double bulb beams, similar to C but having a curve in the shank to fit the bulb; C is a type adapted for channel beams or the flat side of a single bulb beam. The two pieces are of malleable iron and hinged below the swell for the conduit. After slipping over the conduit the drilled ends are brought to-
FIG. 71 – Hanger for channel beams. (page 153)
gether and a 3/8- inch bolt put through both hanger ends and the beam or angle; a nut secures all in place.
The foregoing necessitates the objectionable practice of drilling the beam. Fig. 71 shows a type of clamp requiring no drilling or tapping of beams, but is adapted for channel beams only; it can be used for pipes of larger size than conduit. The clamp is
FIG. 72 – Plate metal hanger. (page 153)
of malleable iron in one piece and draws the conduit securely against the beam by two case-hardened, square-headed set screws.
The type of hanger very generally used in contract-built ships is shown in sketch in Fig. 72.
It is of sheet iron or sheet steel, sometimes thin plate, which is punched or drilled to take conduit of the required size; it is secured by hexagonal-headed bolts through the beam and set up with nuts. For bulb beams, etc., the plate is bent; an angle iron is attached for use against decks or bulkheads.
It has the advantage of being simple and comparatively cheap and of light weight; its disadvantages reside in having to take clown a number of conduits when only one circuit is to be overhauled, and its inconvenience of installation near bends in the conduit. When this type of hanger is installed the number of conduits in any one hanger should be restricted to that which will insure a small amount of labor in handling the conduits for repair work.
Conduit Straps—Conduit straps (Fig. 73), are for securing conduit when run along flat surfaces and are made of the same material as the conduit which they secure.
FIG. 73 – Conduit straps. (page 154)
There are two types, a light, known as A and C, and a heavy, known as B and D. The light straps are made of No. 16 U. S. S. G. sheet iron, or No. 14 B. & S. G. sheet brass; they are used in quarters, etc., where the conduit is not likely to receive mechanical stresses. The heavy straps are used elsewhere and are made of 3/16-inch iron or brass.
The light types are secured with 5/16-inch button-head cap screws, the heavy with 3/8-inch iron, hexagonal tap bolts.
Lock Nut—Single lock nuts, as distinct from the jam nuts for stuffing tubes, are occasionally required for following up a coupling to its place on a joint. They are of cast iron and of commercial pattern.
Cleats—Porcelain cleats (A, Fig. 74) are sometimes used in non-watertight wiring instead of insulators for securing wiring in place. They are of commercial porcelain types in a variety of sizes, and are secured by machine or wood screws as necessary. The cleat is usually reinforced by a metal cap or plate, to hold the pieces of porcelain temporarily in case of breakage or fracture.
Hooks—Three types in general use are shown in Fig. 74. B is a type derived from the post of the upper part of the desk light fixture and intended to be placed in convenient places about staterooms, etc., for hanging the lamp carrier when taken off the base stand.
C is a type for suspending the bight of bell cords and the desk light wires; the hook part is covered by a rubber sleeve for insulation and to prevent chafe.
D is the ordinary commercial 1½-inch cup hook, for the same purpose as C, but for securing in wood only.
Fuses
A fuse is an appliance which is inserted in an electrical circuit to protect that circuit from a current of such a magnitude as
FIG. 74 – Cleats and hooks (page 155)
would overheat and injure the apparatus or the insulation of the wire; the fuse melts and breaks the circuit. Fuse material may be of any metal or alloy; the restricting conditions are, that the material shall melt under the heat generated in the conductor when the maximum permissible current passes, and that the fuse shall be sufficiently substantial to permit ordinary usage in handling, though not to be too bulky. Pure copper has certain advantages, but is not available, the principal objection being that the high temperature of the fused metal introduces a risk from fire.
The determination of fuse dimensions and material is based upon equating the amount of heat generated in the fuse, at the temperature of fusion, with the heat radiated from the surface under the same conditions; the equation eliminates length of fuse and time, but in practice it is found that the length should be many times the diameter to compensate for the cooling effect of the clamps or terminals to which the fuse is attached. The practical determination of proportions for the alloy for fuses for naval use is determined by standards of temperatures of fusion, Fahrenheit, as follows: (Manufacturers differ in variations of mixture and proportion):
Melting Point Lead Tin Bismuth
210° 5 3 8
246° 1 4 5
286° " 1 1
334° " 2 1
334° 2 3 "
The character of the alloy is specified to be such that there will be no reddening or excessive elongation when the current is slowly raised until the temperature of fusion is reached, and the maximum current is to be double that of the rated carrying capacity of the fuse, that is, a fuse rated at 20 amperes should not " blow " below 40 amperes. All fuses should carry 50 per cent of current above their rated capacity without being affected. The carrying capacity, or maximum permissible amperage, is determined by cross sectional area for a given alloy; when the cross section is circular the diameter is taken as the measure of cross-section.
Dynamo Fuse (Fig. 75, A)—It is inserted to bridge the gap between the switchboard terminals for the dynamo leads and the terminals to which the bus bar connections are made.; if a circuit breaker is installed at the switchboard end of the dynamo leads, a fuse- is unnecessary, but if the circuit breaker is mounted on the dynamo headboard a fuse is properly inserted on each leg at the switchboard. Dynamo fuses are copper tipped and designed to mount on 3/8-inch bolts, with 2 1/8-inch distance between centers; the copper tips are proportioned in thickness to the capacity of the fuse. The standard rated capacities are 25, 50, 75, 100, 200, 300, 400, and 500 amperes. The rated capacity is stamped on one of the lugs. Dynamo fuses made entirely of zinc have proved satisfactory.
Switchboard Circuit Fuses—This type is employed to fuse the gap between the circuits on the switchboard and the bus bars.
The type for the former 1892 standard switchboard, and known as the push-clip fuse, is shown in Fig. 75, B and C, which differ from each other mainly in the thickness of the copper clip. The type used with the present standard switchboard is shown in Fig. 75, D. They are of the commercial copper-tipped pattern, designed to mount on No: 10 screw studs, with 1 11/16 inches between centers. The slots in the tips are at right angles. The material is either fuse wire or fuse strip. The rated capacity
FIG. 75 – Types of fuses. (page 157)
is stamped on one of the tips. The actual length of fuse metal must be at least one inch.
The different rated capacities of switchboard fuses are 10, 15, 20, 30, 40, 50, 60, 75, and 100 amperes; when a fuse of greater capacity than 100 amperes is required, as for a motor circuit, a dynamo fuse is employed.
Feeder Box Fuses—Fuses for feeder boxes (Fig. 75, E) are of commercial copper-tipped pattern, designed to mount on No. 8 screws with 1 9/32 inches between centers. The tip slots are lengthwise of the fuse. The actual length of fuse metal must be at least an inch. The rated capacities are the same as for the switchboard circuit fuses, the sizes in common use being 10, 15, 20, 30, 40, and 50 amperes. When placed in the feeder box the length is accommodated by bending the fuse wire around the inside periphery of the mica cup.
Glass-tube Fuses—The fuse for branch junction boxes and distribution boxes is shown in Fig. 75, F.
It consists of a piece of glass tubing 11/8 inch long, over which a centrally perforated copper tip, ¼, inch long by ¼-inch diameter, is cemented at each end. A piece of 4-ampere fuse wire is threaded through the fuse, turned over at each end and soldered to the tip. The tips fit in the clips of the interior fitting for the junction box.
Sounding tubes which have been used in the Navigational Sounding Machine answer well for the glass tube section.
The fuses are rated at 4 amperes, for 80 volt circuits, and 3 amperes for 123-volt circuits.
Tape
There are three varieties: pure Para rubber, vulcanized rubber, and cotton tape; each variety is supplied in three widths ½ inch, ¾ inch, inch, and 1 inch.
All tapes should be of the best commercial grades, of recent manufacture, the surfaces smooth, the body free from holes, the edges straight and without selvage, and the widths even.
Pure Para tape should always be used next the bare copper, when covering a break, splice, etc. It is to be approximately 1/64 inch thick, contain a minimum of 98 per cent of high grade pure Para rubber, and show a maximum of 2 per cent of ash when burned. The color to be brown and the layers separated by paper in the rolls; all rolls to be wrapped first in oil paper and then covered with tin foil.
Vulcanized rubber tape is not suitable for good insulation next a bare wire; it is used as a layer over, and extending beyond, the pure Para tape; being easily injured, it is not suitable for outside layers. It is to be approximately 1/40 inch thick, to contain from 45 to 55 per cent of high grade pure Para rubber, and show from 55 to 65 per cent of ash when burned. The color to be black and the layers separated by linen in the rolls; all rolls to be wrapped in oil paper.
Cotton tape is for use as an outside mechanical layer over pure Para tape, or vulcanized, or both. It is not suitable for the innermost layer when insulation is required. It is to be approximately 1/50 inch thick, to develop between 40 and 45 per cent of ash when burned. The color to be black and both sides of the tape to be frictioned with a rubber compound. The layers of tape in the roll need not be separated, but the rolls must be first covered with tissue paper and then enclosed in tin foil.
Cotton tape and vulcanized tape are not ordinarily very adhesive, but are made so by warming up moderately after wrapping on.
Inspection of Wiring Appliances
Ducts.—Molding—Molding material follows the Navy Department specifications for the particular kind of lumber of which it is to be made.
The molding as made is gauged to the dimensions of the drawing, particularly as to gutters and side walls.
The capping design must contemplate securing to side walls and not to the wall between the gutters.
Pine molding must receive a priming coat of paint directly after manufacture.
Conduit. ---Conduit is first calipered inside and out and the various lengths are measured. Each length is examined internally against a strong light to detect any fins and burs which would injure wire in drawing.
The ends are to be threaded externally for right-handed Couplings; the inner edges must be slightly beveled.
The enamel coating must be of three coats inside and out; this is usually determined on the basis of the thickness and comparison with formerly accepted conduit.
The enamel of three pieces of the conduit is tested by acid; one of each with sulphuric, nitric .and muriatic acid, each acid of 30 per cent strength, the duration of exposure to each acid action being 24 hours.
One piece is subjected for 24 hours to the action of a saturated solution of lye. Enamel which resists the action of the acids will frequently soften under the lye test.
A fourth piece of conduit is subjected to a temperature of 100 C. for two hours. The enamel must not soften or run.
A fifth piece is bent cold at a radius of fifteen times the iron Pipe size; under this condition the enamel should adhere with smooth surface, and without cracks or knuckles.
Flexible conduit is SO little used that it is practically obsolete; what is used is a cotton jacketed hose, whose inspection follows that for hose specifications, the important point being the inspection of the rubber lining.
The rubber compound is to contain 35 per cent fine Para rubber; the composition is tested chemically, and for tensile strength, - elongation and permanent set exactly as prescribed for rubber layers of standard wire, and the prescriptions for test are identical with those for wire.
Box Types.—Box types are mainly to comply with standard drawings as to the various details.
Especial attention should be paid to the following:
Boxes and covers must be drilled to jig to guarantee interchangeability and fit of spares.
The box should be thoroughly painted inside with an air drying enamel. This, whilst not demanded by specifications is important, as the box dimensions have been reduced to the lowest possible limits and the insulating coat is to guard against arcing from the current carrying parts.
The distance between centers of bottom bosses, for holding the interior fittings, must gauge as prescribed by drawing; otherwise the screw holes of new fittings will not register.
The bottom of the box must be well covered by a sheet of mica—micanite in some cases; this is to insulate the block of the interior fitting thoroughly from the bottom of the metal box when the porcelain has absorbed moisture.
Current carrying parts must not be nearer than inch to any metal part of the box, including screws. This does not apply to special boxes and is to be regarded as the minimum; the nearness of live parts to the metal is now so small that, for boxes for conduit, not intended to be secured by screws, the screw well bosses, when inside the box, are usually milled off in practice. It is frequently done also with the lower parts of the ribs for the cover screws.
The micanite plate which separates the fuses in special feeder boxes must be secured at the base and not by tongues extending down the sides; the latter case vitiates the required distance for good insulation.
The cloth insertion sheet rubber packing which lines the cover must be so well cemented on as to insure against tearing off at the edges or from any part of the surface when removing the cover; this is especially to be guarded against when merely edge packing’s are used.
Box types for interior communication circuits are to comply with drawings, and are inspected as explained for other boxes, as the case may apply.
Non-watertight Appliances—These appliances except fuses, gaskets and tape, are inspected in comparison with standard sample, being of the general commercial forms.
Fuses—The main items of consideration in testing fuses is that they shall readily sustain their rated current, shall not blow under a current value of twice the rated value, and shall not redden, nor show excessive elongation under any current value up to that represented by twice the rated carrying capacity for the particular fuse.
A special type of marble panel board is used for the test, on which are assembled: a pair of bus bars; an ammeter; a main line, double-pole, switch; and a “hatchet " switch.
The energy is supplied by three storage batteries at 62 volts. The positive lead is connected to the main switch through one or more rheostats, having capacities of zero to 10 amperes, zero to 100 amperes, and zero to 400 amperes. Short-circuiting the rheostats gives a total capacity of 700 amperes; when fuses of greater capacity than 350 amperes are to be tested, the testing is done from the leads of the main switchboard at the test plate (for generating sets).
The ammeter is connected in the positive lead of the main circuit.
The bus bars have in parallel the following appliances for connecting the fuses in circuit: A non-watertight receptacle, for non-watertight attachment plugs; a 4-way branch junction box, for glass tube fuses; a feeder junction box, for corresponding type of fuse; two stud contacts, for switchboard clip fuses; and two stud contacts for dynamo circuit fuses.
The hatchet switch is a special construction having two oppositely placed knife switches, bent back from a right angle, giving the appearance and name, and having a set of clips to the right and left connected to the line; its use is explained in the following example:
Assume that a 200-ampere dynamo circuit fuse is that to be tested.
The fuse is inserted in the appropriate studs of the bus bar, the line is connected up through the 0-400 ampere rheostat and the hatchet switch is thrown to the right hand contact; in this position the current will pass through the line only and not through the fuse. The current is now adjusted by the rheostat until the ammeter shows 200 amperes. The hatchet switch is then thrown to the left, by which the main line current is transferred through the fuse, but by the construction of the switch the current of the main line is flowing through the fuse before breaking the right-hand connection for the switch; this necessary arrangement obviates any extra current through the fuse incident to breaking contacts in the ordinary way and the fuse will be subjected only to the actual current in circuit.
The hatchet switch is next thrown to the right (fuse cut out) and the main line current raised to 300 amperes; then the switch is thrown to the left, as before, and the fuse subjected to 300 amperes (150 per cent). In both cases the fuse should not be affected.
Without altering the position of the hatchet switch (fuse still in circuit) the current is slowly raised by the rheostat to 400 amperes (double the rated capacity); the fuse should not blow within from ten to thirty seconds after receiving the maximum.
If the fuse blows appreciably below ten seconds, it is rated too high; if for more than 30 seconds, it is rated too low. No reddening or excessive elongation should appear at any stage of the test before blowing.
Molded Gaskets—The specifications for molded gaskets have been cited in the description. Their test follows the same rubber test, chemically, for tensile strength, elongation and permanent set, as explained for rubber layers on wire, for compliance with the specified details. No other test than the gauging of the dimensions externally and of perforations is required.
In selecting a sample for test in the Riehle machine a strip, as long as possible, is cut from the circumference, the cross section being determined by caliper.
Tape—The rubber constituents are determined chemically as for rubber layers on wire. The percentage of rubber in a weighed sample is obtained by burning the sample; the difference between the weight of sample and ash being accepted as the weight of rubber filling.