Chapter XVIII Theater Wiring
The wireman should not fail to consult local rules or inspection departments as to whether any rules conflict with those given below. He must be warned to consult local authorities or rules, too, because safety rules are liable to change.
The purpose of this chapter is to furnish a ready reference work concerning questions of electrical construction in theaters which come up daily in all progressive play houses. To this end the subjects have been arranged in alphabetical order and the practical considerations, as well as extracts from the National Electrical Code governing construction, have been given together. The aim has been to enable the workman to find all information concerning construction work grouped together, so as to obviate the necessity of looking through various parts of the book for the information sought. This order of things will probably avoid the troubles now often caused by overlooking certain points that should be considered.
Aisle Light
Aisle Light.—Figure 151 is an illustration of an aisle light. Such lights are often placed along steps and aisles. The light illuminates only the floor. Aisle lights should be arranged on a separate circuit and controlled by a switch at the door.
Alternating Current
Alternating Current.—All wires of any circuit or mains or sub-mains of any system must be run in the same conduit. Failure to do this will cause an unnecessary drop in voltage and heating of the conduit.
Arc Lamps
Arc Lamps.—For treatment and construction of portable arc lamps, see the chapter on “Portable Stage Equipment”.
Permanently located arc lamps are used about theaters mostly for out-door lighting. Very often, two or more lamps are arranged in front of the house. Such lamps are mostly of the flaming arc lamp type and are hung up high.
In some of the cheaper theaters a pair of arc lamps is used on the stage, but they do not give satisfaction. The light is not even and steady enough and cannot be properly “dimmed”. Where arc lamps are to be arranged for stage illumination they must be suspended amid the scenery and enclosed with wire guards. In some cities the use of arc lamps suspended above the stage is prohibited.
In the auditorium, arc lamps are sometimes installed, but this practice can not be recommended and, with the present high efficiency incandescent lamps, there is but little excuse for it. The only advantage in using arc lamps lies in the first cost of wiring, and this is more than balanced by the difficulties of trimming lamps located in such places. Wherever arc lamps are used it is essential that they be hung high and those that do not naturally throw the light downward must be equipped with suitable reflectors. The question of drop in voltage need not be considered with arc lamps unless runs are very long.
National Electrical Code Rules for Arc Lamps
Arc Lamps in General
Must be provided with reliable stops to prevent carbons from falling out in case the clamps become loose.
All exposed parts must be carefully insulated from the circuit.
Must, for constant-current systems, be provided with an approved hand switch, and an automatic switch that will shunt the current around the carbons, should they fail to feed properly.
The hand switch to be approved, if placed anywhere except on the lamps itself, must comply with requirements for switches on hanger-boards.
Terminals must be designed to secure a thoroughly good and permanent contact with the supply wires, which contact must not become loosened by motion of the lamp during trimming.
Spark arresters must so close the upper orifice of the globe that it will be impossible for any sparks, thrown off by the carbons, to escape.
Series Arc Lamps
Must be carefully isolated from inflammable material.
Must be provided at all times with a glass globe surrounding the arc, and securely fastened upon a closed base. Broken or cracked globes must not be used.
Must be provided with a wire netting (having a mesh not exceeding one and one-fourth inches) around the globe and an approved spark arrester, when readily inflammable material is in the vicinity of the lamps, to prevent escape of sparks of carbon or melted copper.
Outside arc lamps must be suspended at least eight feet above sidewalks. Inside arc lamps must be placed out of reach or suitably protected.
Arc lamps, when used in places where they are exposed to flyings of easily inflammable material, must have the electrodes enclosed completely in a tight globe in such manner as to avoid the necessity for spark arresters.
“Enclosed arc” lamps, having tight inner globes may be used, and the requirements of b and c above would, of course, not apply to them.
Where hanger-boards are not used, lamps must be hung from insulating supports other than their conductors.
Lamps when arranged to be raised and lowered either for carboning or other purposes, shall be connected up with stranded conductors from the last point of support to the lamp, when such conductor is larger than No. 14 B. & S. gauge.
Arc Lamps on Constant-Potential Circuits
Must have a cut-out for each lamp or each series of lamps.
The branch conductors must have a carrying capacity about fifty per cent in excess of the normal current required by the lamp.
Must only be furnished with such resistances or regulators as are enclosed in non-combustible material, such resistances being treated as sources of heat. Incandescent lamps must not be used for this purpose.
Arc Lamps Used as a Part of a Moving-Picture Machine
Must be constructed, so far as practicable, similar to arc lamps of theaters, and wiring to same must not be of less capacity than No. 6 B. & S. gauge. See “Portable Stage Equipment”.
Stage and Gallery Pockets
Must be of approved type, insulated from ground and controlled from switchboard, each receptacle to be of not less than 35 ampere rating for arc lamps nor 15 amperes for incandescent lamps, and each receptacle to be wired to its full capacity. Arc pockets to be wired with wire not smaller than No. 6 B. & S. gauge and incandescent pockets with not less than No. 12 B. & S. gauge.
Plugs for arcs and incandescent pockets must not be interchangeable.
Armored Cable
Armored Cable.—All wires in the stage part of theaters must be enclosed in conduit or armored cable. Armored cable is thus the only flexible conductor allowed for permanent work. This cable is very convenient where wires must be “fished”, or run around beams or other obstacles making many bends necessary. It should, however, be used only where the rigid conduit cannot well be installed and it is advisable to use the latter, even where the additional expense is considerable. Wires run in rigid conduit can be taken out and replaced by new ones at any time, while this is not the case with armored cable. Should a wire incased in armored cable develop a serious fault, the old cable would have to be abandoned and a new circuit run, which in many cases would mean the tearing up of parts of the building.
Where armored cable is to be used great care should be exercised to see that bends are not made too short, and that each length of cable is tested for grounds, short circuits, and open circuits. Special attention must be given to the wires at the place where the armor has been cut. Careless workmen can do great damage at this point. The manner of cutting the armor is shown in Figure 152. Each strand of the armor is partly cut with a saw and may then be broken off, taking care that no sharp edge is left in position to pierce the wire.
Installation rules are given below. Before installing any armored cable, be sure that it is of approved make and guaranteed to pass inspection.
National Electrical Code Rule for Armored Cables
Must be continuous from outlet to outlet or to junction boxes or cabinets, and the armor of the cable must properly enter and be secured to all fittings, and the entire system must be mechanically secured in position.
In case of service connections and main runs, this involves running such armored cable continuously into a main cut-out cabinet or gutter surrounding the panel board, as the case may be.
Must be equipped at every outlet with an approved outlet box or plate, as required in conduit work.
Outlet plates must not be used where it is practicable to install outlet boxes.
For concealed work in walls and ceilings composed of plaster on wooden joist or stud construction, outlet boxes or plates and also cut-out cabinets must be so installed that the front edge will not be more than one-fourth inch back of the finished surface of the plaster, and if this surface is broken or incomplete it shall be repaired so that it will not show any gaps or open spaces around the edges of the outlet box or plate or of the cut-out cabinet. On wooden walls or ceilings, outlet boxes or plates and cut-out cabinets must be so installed that the front edge will either be flush with the finished surface or project therefrom. This will not apply to concealed work in walls or ceilings composed of concrete, tile or other non-combustible material.
In buildings already constructed where the conditions are such that neither outlet box nor plate can be installed, these appliances may be omitted by special permission, provided the armored cable is firmly and rigidly secured in place.
Must have the metal armor of cables permanently and effectually grounded to water piping, gas piping, or other suitable grounds, provided that when connections are made to gas piping, they must be on the street side of the meter. If the armored cable system consists of several separate sections, the sections must be bonded to each other, and the system grounded, or each section may be separately grounded, as required above.
The armor of cables and gas pipes must be securely fastened in outlet boxes, junction boxes, and cabinets, so as to secure good electrical connection.
If armor of cables and metal of couplings, outlet boxes, junction boxes, cabinets, or fittings having protective coating of non-conducting material, such as enamel, are used, such coating must be thoroughly removed from threads of both couplings and the armor of cables, and from surfaces of the boxes, cabinets, and fittings where the armor of cables or ground clamp is secured in order to obtain the requisite good connection. Grounded pipes must be cleaned of rust, scale, etc., at place of attachment of ground clamp. Connections to grounded pipes and to armor of cables must be exposed to view or readily accessible, and must be made by means of approved ground clamps, to which the ground wires must be soldered.
Ground wires must be of copper, at least No. 10 B. & S. gauge (where largest wire contained in cable is not greater than No. 0 B. & S. gauge), and need not be greater than No. 4 B. & S. gauge (where largest wire contained in cable is greater than No. 0 B. & S. gauge). They must be protected from mechanical injury. The ground for the armored cable system is not to be considered as a ground for a secondary system.
When installed in so-called fireproof buildings in course of construction, or afterwards if exposed to moisture, or where it is exposed to the weather, or in damp places, such as breweries, stables, etc., the cable must have a lead covering placed between the outer braid of the conductors and the steel armor. The lead covering is not to be required when the cable is run against brick walls, or laid in ordinary plaster walls unless same are continuously damp.
Where entering junction boxes, and at all other outlets, etc., must be provided with approved terminal fittings which will protect the insulation of the conductors from abrasion, unless such junction or outlet boxes are specially designed and approved for use with the cable.
Junction boxes must always be installed in such a manner as to be accessible.
For alternating-current systems must have the two or more conductors of the circuit enclosed in one metal armor.
All bends must be so made that the armor of the cable will not be injured. The radius of the curve of the inner edge of any bend not to be less than 11⁄2 inches.
Asbestos
Asbestos.—As all wiring in theaters is required to be run in conduit, and metal cabinets are compulsory in this connection, there is but little opportunity to use asbestos. Wherever the use of asbestos is advisable it must conform to the general requirements as given for wooden cutout cabinets, viz.: “for lining wooden cabinets, one-eighth inch rigid asbestos board may be used when firmly secured in place by screws or tacks”.
Attachment Plugs
Attachment Plugs.—Attachment plugs should be used to connect all portable apparatus. All plugs should be of approved type and constructed so as to pull out in case strain is put on them. On the stage, pin-plug connectors should be used in place of attachment plugs, as none of the latter are sufficiently rugged to withstand the hard usage.
National Electrical Code Rules for Attachment Plugs
Link fuse attachment plugs of the types now on the market are considered unsafe, as under entirely possible conditions an arc may be produced when the fuses blow, damaging the plug and perhaps causing fire. Attachment plugs are not approved for more than six hundred and sixty watts or two hundred and fifty volts.
Auditorium
Auditorium.—Two separate systems of lighting are required: See emergency or exit lighting. Metal moulding, as well as armored cable or conduit, is permissible in wiring the auditorium part of the theater.
Auto-Starters
Auto-Starters.—Auto-starters perform the same service with alternating-current motors that resistances do with direct-current motors. They are used with motors from two or three horse power upward, and not generally with the smaller motors.
The following are extracts from the “National Electrical Code” concerning their use:
In all wet, dusty, or linty places, auto-starters, unless equipped with tight casings enclosing all current-carrying parts, must be enclosed in dust-tight fireproof cabinets. Where there is any liability of short circuits, caused by accidental contacts, across their exposed live parts a railing must be erected around them.
The switch on the auto-starter must provide an off position, a running position, and at least one starting position. It must be so arranged that it will be held in off and running position, but not in starting position or without the proper running overload-protection devices in the circuit.
For currents above 30 amperes, lugs, into which the connecting wires may be soldered, or approved solderless connectors must be used. Clamps or lugs will not be required when leads are provided as a part of the device.
The following rules are drawn for rheostats but may also apply to auto-starters:
Where the circuit-breaking device on the motor-starting rheostat disconnects all of the wires of the circuit, the switch called for in this section (to disconnect all apparatus) may be omitted.
Overload-release devices on motor-starting rheostats will not be considered to take the place of the cutout required to protect the motor and the rheostat.
Balconies
Balconies.—The illumination of balconies is a difficult matter. The ceilings under galleries above are always low, and to obtain even illumination requires the use of many small candle-power lamps. These should be set well back so as not to be visible too much to the audience.
Stage-pocket capacity for one or more arc lamps should always be provided. Where there are galleries above, the arc lamps used for stage illumination are generally placed there, but it often happens that a moving-picture machine must be installed and it is very disadvantageous if this must be located in the galleries. Balconies require the same exit and emergency light service as is required in the auditorium.
Batteries
Batteries.—See Portable Stage Equipment.
Bells
Bells.—Systems of call bells are generally arranged between the box office or the manager’s office and the stage switch board; also from the stage switch board to the fly floor by which signals for raising and lowering the curtain may be given; also to the orchestra leader. In some cities all of this wiring is required to be in conduit. These signaling circuits should be carefully installed, for they are as important as any part of the wiring. Only the very best bells and push buttons should be used, and it is advisable to avoid the use of the ordinary annunciator wire so often seen in connection with bell work. Numerous diagrams and much information concerning bell wiring is given in “Modern Wiring Diagrams and Descriptions”, which should be consulted in case some complicated annunciator system is to be installed. Figure 153 is a diagram of a simple call-and-return-call system.
Borders
Borders.—The number of borders used in theaters varies from one to six, the latter number being sufficient for almost any stage. They are generally made of a length about equal to the proscenium opening. The borders placed in the rear are of less importance than those in front and consequently are made shorter and are not provided with so many lights. Each border should have at least three circuits, one for each color; each circuit being taken through a separate dimmer so that any color may be used alone and dimmed as desired.
Figures 154 and 155 show types of borders, and the method of wiring is shown in Figure 156.
Large borders are very heavy and are usually suspended by wire rope and provided with counterweights to make handling easy. The wire rope should be kept well protected by oiling; the moisture given off by fireproofed scenery is liable to rust them very fast, and as the ropes are made up of very fine strands the rust soon cuts entirely through them. The suspending ropes and also cables supplying lights must be long enough to admit of bringing the border within five or six feet of the stage floor for lamp renewals and cleaning. The cleaning is very important as the dust which accumulates may absorb a large part of the light.
The National Electrical Code Rules Governing Border and Proscenium Sidelight Construction
Must be constructed of steel of a thickness not less than No. 20 U. S. sheet metal gauge; treated to prevent oxidation; be suitably stayed and supported; and so designed that flanges of reflectors will protect lamps.
Must be so wired that no set of lamps requiring more than 1,320 watts nor more than 26 receptacles shall be dependent upon one cut-out.
Must be wired in approved conduit or armored cable, each lamp receptacle to be enclosed within an approved outlet box, or the lamp receptacles may be mounted in an iron or steel box, metal to be of a thickness not less than No. 20 U. S. sheet metal gauge treated to prevent oxidation, so constructed as to enclose all wires. Wires to be soldered to lugs of receptacles.
Must be provided with suitable guards to prevent scenery or other combustible material coming in contact with lamps.
Cable for borders must be of approved type and suitably supported; conduit construction must be used from switchboard to point where cables must be flexible to permit of the raising and lowering of border.
For the wiring of the border proper, wire with approved slow-burning insulation must be used.
Borders must be suitably suspended, and if a wire rope is used same must be insulated by at least one strain insulator inserted at the border.
Box Office
Box Office.—The box office is often a very stuffy place in summer and very cold in winter. There should be an outlet for a fan motor, and also one for a heater. Very many box offices depend upon electric heating for comfort in winter. Plenty of light should be provided and the light should be at the ceiling, out of the way, and directly over the ticket window.
Brackets
Brackets.—Any brackets used in theaters should be at least seven feet above the floor. Brackets used for emergency or exit lights must be fitted with keyless sockets. See “Fixtures”.
Branch Circuits
Branch Circuits.—The term, “branch circuit”, as here used refers to the wires leaving the last cut-outs and connecting directly to the lamps or other devices. Mains are often run from the switchboard to various parts of the building to feed cut-out centers, and the branch circuits are then run from these centers. This is often the cheapest method, but it is by no means the best. In a well designed theater all branch circuits lead out from the vicinity of the switchboard so that, in case of any trouble with fuses, they may be replaced without interfering with any part of the audience and in the shortest possible time. This method of wiring involves some long runs of branch circuit wires and Table V, which shows the drop in voltage, was prepared for the convenience of wiremen. If possible the circuits should be so arranged that the lamps fed are closely together so all may receive nearly the same voltage. The drop should not much exceed two per cent.
Table showing drop in voltage due to 6 amperes, with sizes of wire and distances given:
TABLE V.
DROP IN VOLTAGE DUE TO 6 AMPERES WITH SIZE OF WIRE
AND DISTANCE GIVEN.
| Distance in feet | 50 | 75 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 300 |
|---|---|---|---|---|---|---|---|---|---|---|
| Size of Wire No. 14 | 1.58 | 2.37 | 3.16 | 3.95 | 4.74 | 5.53 | 6.32 | 7.11 | 7.90 | 9.48 |
| Size of Wire No. 12 | 0.99 | 1.48 | 1.98 | 2.47 | 2.97 | 3.45 | 3.96 | 4.45 | 4.95 | 5.94 |
| Size of Wire No. 10 | 0.63 | 0.94 | 1.25 | 1.56 | 1.87 | 2.19 | 2.50 | 2.81 | 3.12 | 3.75 |
| Size of Wire No. 8 | 0.39 | 0.59 | 0.78 | 0.97 | 1.17 | 1.36 | 1.56 | 1.75 | 1.95 | 2.34 |
National Electrical Code Rules Governing Size of Wire for Branch Circuits and Fuses for Same
No wire smaller than No. 14 B. & S. gauge must be used.
Each branch circuit must be protected by fuses, which must be so placed that no set of small motors, small heating devices, or incandescent lamps, whether grouped on one fixture or on several fixtures or pendants (nor more than 16 sockets or receptacles) requiring more than 660 watts, will be dependent upon one cut-out.
By special permission, in cases where wiring equal in size and insulation to No. 14 B. & S. gauge approved rubber-covered wire is carried direct into keyless sockets or receptacles, and where the location of sockets and receptacles is such as to render unlikely the attachment of flexible cords thereto, the circuits may be so arranged that not more than 1,320 watts (or thirty-two sockets or receptacles) will be dependent upon the final cut-out.
Except for signs and outline lighting, sockets and receptacles will be considered as requiring not less than 40 watts each.
All branches or taps, from any three-wire system, which are directly connected to lamp sockets or other translating devices, must be run as two-wire circuits if the fuses are omitted in the neutral, or if the difference of potential between the two outside wires is over 250 volts, and both wires of such branch or tap circuits must be protected by proper fuses.
The above shall also apply to motors, except that small motors may be grouped under the protection of a single set of fuses, provided the rated capacity of the fuses does not exceed 10 amperes.
When 1,320 watts are dependent upon one fusible cut-out, as is allowed in theater wiring, outline lighting and large chandeliers, the fuses may be in accordance with the following:
| 125 volts or less | 20 amperes |
| 125 to 250 volts | 10 amperes |
Bus-Bars
Bus-Bars.—Bus-bars may be made of bare metal. They must, however, be protected against accidental contact. The metal should be ample so that it will not heat more than 50 degrees Fahrenheit above the surrounding air.
It is customary to calculate the metal needed, on the basis of 1,000 amperes per square-inch cross section. On this basis bars of the sizes given below would have the carrying capacities in amperes given in the body of the table.
TABLE VI.
CURRENT-CARRYING CAPACITY OF BUS-BARS.
| Thickness | 2⁄32 | 3⁄32 | 4⁄32 | 5⁄32 | 6⁄32 | 7⁄32 | 8⁄32 | 9⁄32 | 10⁄32 | 12⁄32 | 16⁄32 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Width in In- ches | 1⁄2 | 30 | 45 | 60 | 75 | 90 | 105 | 120 | 135 | 150 | 165 | 180 | |
| 5⁄8 | 37 | 57 | 75 | 94 | 108 | 132 | 150 | 168 | 188 | 206 | 225 | ||
| 6⁄8 | 45 | 68 | 90 | 112 | 135 | 158 | 180 | 202 | 225 | 248 | 270 | ||
| 7⁄8 | 53 | 79 | 105 | 130 | 158 | 184 | 210 | 236 | 263 | 289 | 315 | ||
| 1 | .0 | 60 | 90 | 120 | 150 | 180 | 210 | 240 | 270 | 300 | 330 | 360 | |
| 1 | 1⁄4 | 75 | 112 | 150 | 188 | 225 | 263 | 300 | 338 | 375 | 412 | 450 | |
| 1 | 1⁄2 | 90 | 135 | 180 | 225 | 270 | 315 | 360 | 405 | 450 | 495 | 540 | |
| 1 | 3⁄4 | 105 | 157 | 210 | 263 | 315 | 367 | 420 | 473 | 525 | 577 | 630 | |
| 2 | .00 | 120 | 180 | 240 | 300 | 360 | 420 | 480 | 540 | 600 | 660 | 720 | |
| 3 | .00 | 180 | 270 | 360 | 450 | 540 | 630 | 720 | 810 | 900 | 990 | 1080 | |
Cabinets
Cabinets.—Cabinets are required to enclose all fuses. It is advised that they be arranged so that it will not be necessary to open the fuse compartment to operate switches.
Care should be exercised in locating cut-out cabinets. They should be in a dry place, easily accessible to authorized persons, and not accessible to the general public or miscellaneous employes. If too accessible they are likely to be made receptacles for all sorts of rubbish. Wooden or composition cabinets must not be used in theaters. Use only approved cabinets.
In some cities special rules, governing the construction of cabinets for theaters, exist and these should be looked up.
Cables
Cables.—For construction rules, see “Stage Cables” in the chapter on “Portable Stage Equipment”. Cables are required to connect border lights. The cable is usually run from an outlet on the grid floor above the center of the border. It must be long enough to allow the border to be lowered for the cleaning and renewal of lamps. The slack cable must be taken up when the border is raised and some provision must be made to support the cable without injury to the insulation. Wire ropes or cables are generally used to support the borders, but the lower end, which is handled by the stage crew, is of ordinary manilla rope. Wire cables must be insulated from the border by strain insulators.
Canopies
Canopies.—Very many theaters are provided with canopies which extend over the street. Sometimes these are fitted out with glass signs behind which incandescent lamps are installed. Often, also, a row of lights is arranged around the bottom of the canopy ceiling. The number of lights to be used depends upon the design of the canopy, but the effect is best if a large number of small candle-power lamps are used. These lamps should be of low intrinsic brilliancy. If possible, the lamps and sockets should be arranged to be out of the weather. In addition to the small outline lamps, other lights are often placed under canopy to provide bright illumination. Each circuit may carry 1,320 watts.
National Electrical Code Rule
Where insulating joints are required, fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings, or from plaster walls or ceilings on metal lathing, and from outlet boxes.
Canopy insulators must be securely fastened in place, so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated.
Carriage Call
Carriage Call.—See “Program Board”.
Carrying Capacity of Wires
Carrying Capacity of Wires.—Table VII is designed to help the wiremen select the proper size of wire to use in supplying a certain number of lights. The first column at the left gives the B. & S. gauge number. The second column gives the number of amperes allowed on each wire according to the National Electrical Code. The third column gives the distance in feet which will cause a loss of 2 volts with the current given; thus a current of 70 amperes in a No. 4 B. & S. gauge wire will lose 2 volts over a distance of 56 feet. The proper size of wire to be used can easily be determined from the table. The loss will always be in proportion to the product of distance and current. The balance of the table is devoted to showing the number of watts and lamps of various sizes the wires will be allowed to supply.
Ceiling Fans
Ceiling Fans.—Must be hung from insulated hooks, or else there must be an insulator interposed between the motor and its support. Not more than 660 watts may be on one circuit.
Chandeliers
Chandeliers.—Large and elaborate chandeliers are sometimes used in the center of the auditorium ceiling for purposes of illumination. Such chandeliers should be suspended in a manner which will admit of readily raising or lowering them for lamping up or repairs. For rules governing wiring, see “Fixtures”.
TABLE SHOWING CARRYING CAPACITY OF WIRES; DISTANCE TO WHICH FULL LOAD MAY BE CARRIED AT 2 VOLTS DROP AND NUMBER OF LIGHTS EQUIVALENT TO FULL CURRENT GIVEN.
| B. & S. Gage | Rub- ber Insu- lation | Dis- tance in Feet Caus- ing a Loss of 2 Volts | Total Capacity in Watts | Total Number of Lamps of Different Voltages and Wattages that may be supplied | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 25-Watt | 40-Watt | 60-Watt | 100-Watt | 150-Watt | 250-Watt | |||||||||||
| Am- peres | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | ||
| 14 | 15 | 26 | 1650 | 3300 | 66 | 132 | 41 | 82 | 27 | 54 | 16 | 33 | 11 | 22 | 6 | 13 |
| 12 | 20 | 30 | 2200 | 4400 | 88 | 176 | 55 | 110 | 36 | 73 | 22 | 44 | 14 | 29 | 8 | 17 |
| 10 | 25 | 38 | 2750 | 5500 | 110 | 220 | 68 | 137 | 46 | 91 | 27 | 55 | 18 | 36 | 11 | 22 |
| 8 | 35 | 43 | 3850 | 7700 | 154 | 308 | 96 | 192 | 64 | 128 | 38 | 77 | 25 | 61 | 15 | 30 |
| 6 | 50 | 50 | 5500 | 11000 | 220 | 440 | 137 | 275 | 91 | 183 | 55 | 110 | 36 | 73 | 22 | 44 |
| 5 | 55 | 56 | 6050 | 12100 | 242 | 484 | 151 | 302 | 100 | 201 | 60 | 121 | 40 | 80 | 24 | 48 |
| 4 | 70 | 56 | 7700 | 15400 | 308 | 616 | 192 | 385 | 128 | 256 | 77 | 154 | 49 | 99 | 30 | 61 |
| 3 | 80 | 61 | 8800 | 17600 | 352 | 704 | 220 | 440 | 146 | 292 | 88 | 176 | 58 | 117 | 35 | 70 |
| 2 | 90 | 68 | 9900 | 19800 | 396 | 792 | 247 | 494 | 165 | 330 | 99 | 198 | 66 | 132 | 39 | 78 |
| 1 | 100 | 67 | 11000 | 22000 | 440 | 880 | 275 | 550 | 183 | 366 | 110 | 220 | 73 | 146 | 44 | 88 |
| 0 | 125 | 78 | 13750 | 27500 | 550 | 1100 | 343 | 686 | 229 | 458 | 137 | 274 | 91 | 182 | 55 | 110 |
| 00 | 150 | 82 | 16500 | 33000 | 660 | 1320 | 412 | 824 | 275 | 550 | 165 | 330 | 110 | 220 | 66 | 132 |
| 000 | 175 | 89 | 19250 | 38500 | 770 | 1540 | 481 | 962 | 320 | 640 | 192 | 384 | 128 | 256 | 77 | 154 |
| 0000 | 225 | 87 | 24750 | 49500 | 990 | 1980 | 618 | 1236 | 412 | 824 | 247 | 404 | 165 | 330 | 99 | 198 |
| 200000 | 200 | 92 | 22000 | 44000 | 880 | 1760 | 550 | 1100 | 367 | 734 | 220 | 440 | 146 | 292 | 88 | 176 |
| 300000 | 275 | 101 | 30250 | 60500 | 1210 | 2420 | 756 | 1512 | 504 | 1008 | 302 | 604 | 201 | 402 | 121 | 242 |
| 400000 | 325 | 114 | 35750 | 71500 | 1430 | 2860 | 893 | 1786 | 596 | 1192 | 357 | 714 | 238 | 476 | 143 | 286 |
| 500000 | 400 | 117 | 44000 | 88000 | 1760 | 3520 | 1100 | 2200 | 733 | 1455 | 440 | 880 | 293 | 586 | 176 | 352 |
| 600000 | 450 | 123 | 49500 | 99000 | 1980 | 3960 | 1237 | 2474 | 825 | 1650 | 495 | 990 | 330 | 660 | 198 | 396 |
| 700000 | 500 | 130 | 55000 | 110000 | 2200 | 4400 | 1375 | 2750 | 916 | 1832 | 550 | 1100 | 366 | 732 | 220 | 440 |
| 800000 | 550 | 135 | 60500 | 121000 | 2420 | 4840 | 1512 | 3024 | 1008 | 2016 | 605 | 1210 | 403 | 806 | 242 | 484 |
| 900000 | 600 | 139 | 66000 | 132000 | 2640 | 5280 | 1650 | 3300 | 1100 | 2200 | 660 | 1320 | 440 | 880 | 264 | 528 |
| 1000000 | 650 | 143 | 71500 | 143000 | 2860 | 5720 | 1787 | 3574 | 1191 | 2382 | 715 | 1430 | 476 | 952 | 286 | 572 |
| 1100000 | 690 | 147 | 75900 | 151800 | 3036 | 6072 | 1897 | 3794 | 1264 | 2528 | 759 | 1518 | 506 | 1012 | 303 | 606 |
| 1200000 | 730 | 151 | 80300 | 160600 | 3212 | 6424 | 2007 | 4014 | 1338 | 2676 | 803 | 1606 | 535 | 1070 | 321 | 642 |
| 1300000 | 770 | 155 | 84700 | 169400 | 3388 | 6776 | 2117 | 4234 | 1412 | 2824 | 847 | 1694 | 564 | 1128 | 338 | 676 |
| 1400000 | 810 | 161 | 89100 | 178200 | 3564 | 7128 | 2227 | 4454 | 1485 | 2970 | 891 | 1782 | 594 | 1188 | 356 | 712 |
| 1500000 | 850 | 164 | 93500 | 187000 | 3740 | 7480 | 2337 | 4674 | 1558 | 3116 | 935 | 1870 | 623 | 1246 | 374 | 748 |
| B. & S. Gage | Rub- ber Insu- lation | Dis- tance in Feet Caus- ing a Loss of 2 Volts | Total Capacity in Watts | Total Number of Lamps of Different Voltages and Wattages that may be supplied | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 25-Watt | 40-Watt | 60-Watt | ||||||||
| Am- peres | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | ||
| 14 | 15 | 26 | 1650 | 3300 | 66 | 132 | 41 | 82 | 27 | 54 |
| 12 | 20 | 30 | 2200 | 4400 | 88 | 176 | 55 | 110 | 36 | 73 |
| 10 | 25 | 38 | 2750 | 5500 | 110 | 220 | 68 | 137 | 46 | 91 |
| 8 | 35 | 43 | 3850 | 7700 | 154 | 308 | 96 | 192 | 64 | 128 |
| 6 | 50 | 50 | 5500 | 11000 | 220 | 440 | 137 | 275 | 91 | 183 |
| 5 | 55 | 56 | 6050 | 12100 | 242 | 484 | 151 | 302 | 100 | 201 |
| 4 | 70 | 56 | 7700 | 15400 | 308 | 616 | 192 | 385 | 128 | 256 |
| 3 | 80 | 61 | 8800 | 17600 | 352 | 704 | 220 | 440 | 146 | 292 |
| 2 | 90 | 68 | 9900 | 19800 | 396 | 792 | 247 | 494 | 165 | 330 |
| 1 | 100 | 67 | 11000 | 22000 | 440 | 880 | 275 | 550 | 183 | 366 |
| 0 | 125 | 78 | 13750 | 27500 | 550 | 1100 | 343 | 686 | 229 | 458 |
| 00 | 150 | 82 | 16500 | 33000 | 660 | 1320 | 412 | 824 | 275 | 550 |
| 000 | 175 | 89 | 19250 | 38500 | 770 | 1540 | 481 | 962 | 320 | 640 |
| 0000 | 225 | 87 | 24750 | 49500 | 990 | 1980 | 618 | 1236 | 412 | 824 |
| 200000 | 200 | 92 | 22000 | 44000 | 880 | 1760 | 550 | 1100 | 367 | 734 |
| 300000 | 275 | 101 | 30250 | 60500 | 1210 | 2420 | 756 | 1512 | 504 | 1008 |
| 400000 | 325 | 114 | 35750 | 71500 | 1430 | 2860 | 893 | 1786 | 596 | 1192 |
| 500000 | 400 | 117 | 44000 | 88000 | 1760 | 3520 | 1100 | 2200 | 733 | 1455 |
| 600000 | 450 | 123 | 49500 | 99000 | 1980 | 3960 | 1237 | 2474 | 825 | 1650 |
| 700000 | 500 | 130 | 55000 | 110000 | 2200 | 4400 | 1375 | 2750 | 916 | 1832 |
| 800000 | 550 | 135 | 60500 | 121000 | 2420 | 4840 | 1512 | 3024 | 1008 | 2016 |
| 900000 | 600 | 139 | 66000 | 132000 | 2640 | 5280 | 1650 | 3300 | 1100 | 2200 |
| 1000000 | 650 | 143 | 71500 | 143000 | 2860 | 5720 | 1787 | 3574 | 1191 | 2382 |
| 1100000 | 690 | 147 | 75900 | 151800 | 3036 | 6072 | 1897 | 3794 | 1264 | 2528 |
| 1200000 | 730 | 151 | 80300 | 160600 | 3212 | 6424 | 2007 | 4014 | 1338 | 2676 |
| 1300000 | 770 | 155 | 84700 | 169400 | 3388 | 6776 | 2117 | 4234 | 1412 | 2824 |
| 1400000 | 810 | 161 | 89100 | 178200 | 3564 | 7128 | 2227 | 4454 | 1485 | 2970 |
| 1500000 | 850 | 164 | 93500 | 187000 | 3740 | 7480 | 2337 | 4674 | 1558 | 3116 |
| B. & S. Gage | Rub- ber Insu- lation | Dis- tance in Feet Caus- ing a Loss of 2 Volts | Total Capacity in Watts | Total Number of Lamps of Different Voltages and Wattages that may be supplied | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 100-Watt | 150-Watt | 250-Watt | ||||||||
| Am- peres | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | 110 V. | 220 V. | ||
| 14 | 15 | 26 | 1650 | 3300 | 16 | 33 | 11 | 22 | 6 | 13 |
| 12 | 20 | 30 | 2200 | 4400 | 22 | 44 | 14 | 29 | 8 | 17 |
| 10 | 25 | 38 | 2750 | 5500 | 27 | 55 | 18 | 36 | 11 | 22 |
| 8 | 35 | 43 | 3850 | 7700 | 38 | 77 | 25 | 61 | 15 | 30 |
| 6 | 50 | 50 | 5500 | 11000 | 55 | 110 | 36 | 73 | 22 | 44 |
| 5 | 55 | 56 | 6050 | 12100 | 60 | 121 | 40 | 80 | 24 | 48 |
| 4 | 70 | 56 | 7700 | 15400 | 77 | 154 | 49 | 99 | 30 | 61 |
| 3 | 80 | 61 | 8800 | 17600 | 88 | 176 | 58 | 117 | 35 | 70 |
| 2 | 90 | 68 | 9900 | 19800 | 99 | 198 | 66 | 132 | 39 | 78 |
| 1 | 100 | 67 | 11000 | 22000 | 110 | 220 | 73 | 146 | 44 | 88 |
| 0 | 125 | 78 | 13750 | 27500 | 137 | 274 | 91 | 182 | 55 | 110 |
| 00 | 150 | 82 | 16500 | 33000 | 165 | 330 | 110 | 220 | 66 | 132 |
| 000 | 175 | 89 | 19250 | 38500 | 192 | 384 | 128 | 256 | 77 | 154 |
| 0000 | 225 | 87 | 24750 | 49500 | 247 | 404 | 165 | 330 | 99 | 198 |
| 200000 | 200 | 92 | 22000 | 44000 | 220 | 440 | 146 | 292 | 88 | 176 |
| 300000 | 275 | 101 | 30250 | 60500 | 302 | 604 | 201 | 402 | 121 | 242 |
| 400000 | 325 | 114 | 35750 | 71500 | 357 | 714 | 238 | 476 | 143 | 286 |
| 500000 | 400 | 117 | 44000 | 88000 | 440 | 880 | 293 | 586 | 176 | 352 |
| 600000 | 450 | 123 | 49500 | 99000 | 495 | 990 | 330 | 660 | 198 | 396 |
| 700000 | 500 | 130 | 55000 | 110000 | 550 | 1100 | 366 | 732 | 220 | 440 |
| 800000 | 550 | 135 | 60500 | 121000 | 605 | 1210 | 403 | 806 | 242 | 484 |
| 900000 | 600 | 139 | 66000 | 132000 | 660 | 1320 | 440 | 880 | 264 | 528 |
| 1000000 | 650 | 143 | 71500 | 143000 | 715 | 1430 | 476 | 952 | 286 | 572 |
| 1100000 | 690 | 147 | 75900 | 151800 | 759 | 1518 | 506 | 1012 | 303 | 606 |
| 1200000 | 730 | 151 | 80300 | 160600 | 803 | 1606 | 535 | 1070 | 321 | 642 |
| 1300000 | 770 | 155 | 84700 | 169400 | 847 | 1694 | 564 | 1128 | 338 | 676 |
| 1400000 | 810 | 161 | 89100 | 178200 | 891 | 1782 | 594 | 1188 | 356 | 712 |
| 1500000 | 850 | 164 | 93500 | 187000 | 935 | 1870 | 623 | 1246 | 374 | 748 |
National Electrical Code Rules for Fusing Chandelier Circuits
When 1,320 watts are dependent upon one cut-out, as is allowed in theater wiring, outline lighting, and large chandeliers, the fuse may be in accordance with the following:
| 125 volts or less | 20 amperes |
| 125 to 250 volts | 10 amperes |
Circuit Breakers
Circuit Breakers.—Circuit breakers are not used much about theaters. They are used mostly in connection with motors and on switchboards of isolated plants. They are more sensitive and quicker to act than fuses and, in case of a blow-out, can be more easily replaced. Where circuit breakers are used it is good practice to set them for a higher amperage than the fuses so that, in case of a heavy short circuit, the breaker may act while the fuse will take care of an overload which comes on more gradually.
National Electrical Code Rides for Circuit Breakers
With motors an automatic circuit breaker, disconnecting all wires of the circuit, may serve as both switch and cut-out.
Where the circuit-breaking device on the motor-starting rheostat disconnects all wires of the circuit, the switch may be omitted.
Circuit breakers must not be set more than thirty per cent above the allowable carrying capacity of the wires, unless a fusible cut-out is also installed on the circuit.
When installed without other automatic overload protective devices, automatic overload circuit breakers must have the poles and trip coils so arranged as to afford complete protection against overloads and short circuits and, if also used in place of the switch, must be so arranged that no one pole can be opened manually without disconnecting all the wires.
Concealed Work
Concealed Work.—All concealed work must be in conduit or armored cable. Wherever possible, rigid conduit should be used. Armored cable should be used only where the whole cable may at any time be withdrawn, or where it is impracticable to use rigid conduit.
Conduit Work
Conduit Work.—This is now considered the standard method of construction. It is, however, somewhat over-rated and, especially in wet places, has led to much disappointment. It is generally recognized that wires, placed in conduit, will cause more trouble than those placed in any other standard manner. The trouble is, however, confined to the interior of the conduit and, if the conduit system be kept in good order, and fuses at their proper limit, there is no chance of fire from the wire confined within the conduit.
There are three points which, if carefully observed, will avoid most, if not all, of the conduit troubles:
Avoid as far as possible locating conduit in wet or damp places.
Run all conduits so that they will drain.
Give particular attention to joints in outlet or junction boxes; tape them heavily; and arrange them so they are not pressed against metal more than is necessary; use large boxes.
Wires used in conduits must have approved rubber insulation and double braid.
National Electrical Code Rules for Wires and Interior Conduits
Wires for Conduit Work
Must have an approved rubber insulated covering (Type Letter R. D.), and must within the conduit tubing be without splices or taps.
Must not be drawn in until all mechanical work on the building has been, as far as possible, completed.
Conductors in vertical conduit risers must be supported within the conduit system in accordance with the following:
No. 14 to 0 every 100 feet
No. 00 to 0000 every 80 feet
No. 0000 to 350,000 C. M. every 60 feet
350,000 C. M. to 500,000 C. M. every 50 feet
500,000 C. M. to 750,000 C. M. every 40 feet
750,000 C. M. every 35 feet
The following methods of supporting cables are recommended:
(1) A turn of 90 degrees in the conduit system will constitute a satisfactory support.
(2) Junction boxes may be inserted in the conduit system at the required intervals, in which insulating supports of approved type must be installed and secured in a satisfactory manner so as to withstand the weight of the conductors attached thereto, the boxes to be provided with proper covers.
(3) Cables may be supported in approved junction boxes on two or more insulating supports so placed that the conductors will be deflected at an angle of not less than 90 degrees, and carried a distance of not less than twice the diameter of the cable from its vertical position. Cables so suspended may be additionally secured to these insulators by tie wires. Other methods may be used if specially approved.
Must, for alternating-current systems, have two or more wires of a circuit drawn in the same conduit. It is suggested that this be done for direct-current systems, also, so that they may be changed to alternating systems at any time, induction troubles preventing such a change if the wires are in separate conduits.
Except in the case of stage pocket and border circuits the same conduit must not contain more than four two-wire, or three three-wire circuits of the same system, except by special permission, and must never contain circuits of different systems.
Interior Conduits
No conduit smaller than one-half inch electrical-trade size shall be used.
Must be continuous from outlet to outlet or to junction boxes or cabinets, and the conduit must properly enter, and be secured to all fittings and the entire system must be mechanically secured in position. In case of service connections and main runs, this involves running each conduit continuously into a main cut-out cabinet or gutter surrounding the panel board, as the case may be. Departure from this rule may be authorized in case of underground services by special permission.
Must be first installed as a complete conduit system, without the conductors.
Must be equipped at every outlet with an approved outlet box or plate. At exposed ends of conduit (but not at fixture outlets), where wires pass from the conduit system without splice, joint, or tap, an approved fitting, having separately bushed holes for each conductor, must be used. Departure from this rule may be authorized by special permission. Outlet plates must not be used where it is practicable to install outlet boxes.
For concealed work in walls and ceilings composed of plaster on wooden joist or stud construction, outlet boxes or plates, and also cut-out cabinets must be so installed that the front edge will not be more than one-fourth inch back of the finished surface of the plaster; and if this surface is broken or incomplete it shall be repaired so that it will not show any gaps or open spaces around the edges of the outlet box or plate or of the cut-out cabinet. On wooden walls or ceilings, outlet boxes or plates and cut-out cabinets must be so installed that the front edge will either be flush with the finished surface or project therefrom. This will not apply to concealed work in walls or ceilings composed of concrete, tile or other non-combustible material.
In buildings already constructed where the conditions are such that neither outlet box or plate can be installed, these appliances may be omitted, providing the conduit ends are bushed and secured.
It is suggested that outlet boxes and fittings, having conductive coatings, be used in order to secure better electrical contact at all points through the conduit system.
Metal conduits, where they enter junction boxes and at all other outlets, etc., must be provided with approved bushings or fastening plates fitted so as to protect wire from abrasion, except when such protection is obtained by the use of approved nipples, properly fitted in boxes or devices.
Must have the metal of the conduit permanently and effectually grounded to water piping, gas piping, or other suitable grounds, provided that when connections are made to gas piping, they must be on the street side of the meter. If the conduit system consists of several separate sections, the sections must be bonded to each other, and the system grounded; or each section may be separately grounded, as required above. Where short sections of conduit (or pipe of equivalent strength) are used for the protection of exposed wiring on side walls, and such conduit or pipe and wiring is installed as required by the Code Rules, the conduit or pipe need not be grounded.
Conduits and gas pipes must be securely fastened in outlet boxes, junction boxes, and cabinets, so as to secure good electrical connections.
If conduits, couplings, outlet boxes, junction boxes, cabinets or fittings, having protective coating of non-conducting material such as enamel, are used, such coating must be thoroughly removed from threads of both couplings and conduit, and such surfaces of boxes, cabinets, and fittings, where the conduit or group clamp is secured, in order to obtain the requisite good connection. Grounded pipes must be cleaned of rust, scale, etc., at place of attachment of ground clamp.
Connections to grounded pipes and to conduits must be exposed to view or readily accessible, and must be made by means of approved ground clamps to which the ground wires must be soldered.
Ground wires must be of copper, at least No. 10 B. & S. gauge (where largest wire contained in conduit is not greater than No. 0 B. & S. gauge), and need not be greater than No. 4 B. & S. gauge (where largest wire contained in conduit is greater than No. 0 B. & S. gauge). They shall be protected from mechanical injury. The ground on the conduit system is not to be considered as a ground for a secondary system.
Junction boxes must always be installed in such a manner as to be accessible.
All elbows or hands must be so made that the conduit will not be injured. The radius of the curve of the inner edge of any elbow must not be less than three and one-half inches, and must have not more than the equivalent of four quarter bends from outlet to outlet, the bends at the outlets not being counted.
Contacts
Contacts.—Must be mounted on non-combustible non-absorption insulated bases. Other materials than slate, marble, or porcelain must be submitted for special examination before being used.
Cord
Cord.—The use of flexible cord should be reduced to a minimum. Wherever drop lights are necessary they should be wired with reinforced cord or stage cable.
Current Taps
Current Taps.—Must be of approved construction and may be used if properly installed.
National Electrical Code Rules for Current Taps
Where, in addition to sockets or receptacles already installed, connections are desired to lighting circuits for portable lamps, for motors, or other special appliances requiring only small amounts of current, multiple-current taps may be used, provided the entire circuit does not require more than 660 watts, and provided their use will not, under any conditions, involve a departure from the requirements of Rule 23-d of the National Electrical Code. Current taps must not be used in key or pull sockets if the device, controlled through such sockets, requires more than 250 watts.
Cut-Outs
Cut-Outs.—All cut-outs should be on the stage switchboard. This requires considerable extra wire, but it will be profitable in the end. Fuses should be inspected occasionally to see that contacts are bright and screws kept tight. There is everywhere a very strong tendency to over-fuse, and the principal reason for it is the failure to keep screws tightly fastened.
There is no fuse better than the plug fuse but it is not permitted with voltages higher than 125 or with more than 30 amperes. Refillable fuses must not be used. Cartridge fuses, especially, require to be kept clean. The spring contacts on these often grow weak and cause heating which helps to blow the fuse. The neutral fuse in three-wire installations should be larger than the outside fuses. Link fuses should be avoided on account of the delay that may be caused through difficulty of installing.
It is advisable not to place switches in the same cabinet with fuses.
National Electrical Code Rules for Automatic Cut-outs (Fuses and Circuit-Breakers)
Constant-Potential Systems
Must be placed on all service wires, either overhead or underground, in the nearest accessible place to the point where they enter the building, inside the walls, and arranged to cut off the entire current from the building. Departure from this rule may be authorized only under special permission in writing. Where the service switch is inside the building, the cut-out required by this section must be placed so as to protect it.
For three-wire (not three-phase) systems the fuse in the neutral wire may be omitted, provided the neutral wire is of equal carrying capacity to the larger of the outside wires and is grounded.
Must be placed at every point where a change is made in the size of wire (unless the cut-out in the larger wire will protect the smaller). For three-wire direct current or single-phase systems the fuse in the neutral wire, except that called for under Section d, may be omitted, provided the neutral wire is grounded.
Must be in plain sight, or enclosed in an approved cabinet, and readily accessible. They must not be placed in the canopies or shells of fixtures. Link fuses may be used only when mounted on approved bases and must be enclosed in dust-tight, fireproofed cabinets, except on switchboards.
Must be so placed that no set of small motors, small heating devices, or incandescent lamps, whether grouped on one fixture or on several fixtures or pendants (nor more than 16 sockets or receptacles) requiring more than 660 watts, will be dependent upon one cut-out.
By special permission, in cases where wiring equal in size and insulation to No. 14 B. & S. gauge approved rubber-covered wire is carried direct into keyless sockets or receptacles, and where the location of sockets and receptacles is such as to render unlikely the attachment of flexible cords thereto, the circuits may be so arranged that not more than 1,320 watts (or thirty-two sockets or receptacles) will be dependent upon the final cut-out. Except for signs and outline lighting, sockets and receptacles will be considered as requiring not less than 40 watts each.
All branches or taps from any three-wire system which are directly connected to lamp sockets or other translating devices, must be run as two-wire circuits if the fuses are omitted in the neutral or if the difference of potential between the two outside wires is over 250 volts, and both wires of such branch or tap circuits must be protected by proper fuses.
The above shall also apply to motors, except that small motors may be grouped under the protection of a single set of fuses, provided the rated capacity of the fuses does not exceed 10 amperes. When 1,320 watts are dependent upon one fusible cut-out, as is allowed in theater wiring, outline lighting, and large chandeliers, the fuses may be in accordance with the following:
| 125 volts or less | 20 amperes |
| 125 to 250 volts | 10 amperes |
The rated capacity of fuses must not exceed the allowable carrying capacity of the wire. Circuit breakers must not be set more than 30 per cent above allowable carrying capacity of the wire, unless a fusible cut-out is also installed on the circuit. Fixture wire or flexible cord of No. 18 B. & S. gauge, will be considered as properly protected by 10-ampere fuses.
Each wire of motor circuits, except on main switchboard or when otherwise subject to competent supervision, must be protected by an approved fuse whether automatic overload circuit breakers are installed or not. Single-phase motors may have one side protected by an approved automatic overload circuit breaker only if the other side is protected by an approved fuse.
For circuits having a maximum capacity greater than that for which enclosed fuses are approved, circuit breakers alone will be approved. The ordinary porcelain link fuse cut-out will not be approved. Link fuses may be used only when mounted on slate or marble bases conforming to the rules, and must be enclosed in dust-tight, fire-proofed cabinets, except on switchboards located well away from combustible material, as in the ordinary engine and dynamo room, and where these conditions will be maintained.
Damp Places
Damp Places.—It is best to avoid wiring in damp places if possible. If wires must be run in such places, they should be lead covered. If armored cable is used, the wires in cable must be incased in lead. Weatherproof sockets must be used and the use of cords should be avoided. Where cords must be used they should be of the brewery or packing-house type. If outside of the theater, proper open work may be used. Conduit work is permissible but not advisable, except where wires are subject to mechanical injury.
Decorative Lighting Systems
Decorative Lighting Systems.—The commercial decorative lighting systems are not suitable for use inside of theaters and should be used only outside.
National Electrical Code Rule for Decorative Lighting Systems
Special permission may be given in writing for the temporary installation of approved systems of decorative lighting, provided the difference of potential between the wires of any circuit shall not be over 150 volts and also provided that no group of lamps requiring more than 1,320 watts shall be dependent on one cut-out.
Dimmers
Dimmers.—“Dimmer” is the name given to the resistances which are used to dim the electric lights on the stage. They are usually mounted at the top or bottom of the switchboard with the operating handles in easy reach of the operator. A dimmer should be provided for each color in every border light and also for the foot lights. In some cases the proscenium side lights are also arranged for several colors. The dimmers should be mounted so that each one is directly above the switch which controls the circuit to which it belongs. They should be protected by wire guards against rubbish, which is likely to accumulate among them if they are not enclosed. Good ventilation must be provided. A certain dimmer can be used only while the amperage remains within the proper limitations. If carbon lamps, for instance, are changed for tungsten, the amperage will be much reduced and the dimmer may not work properly.
Modern dimmers are all of the interlocking type so that the whole bank may be worked together or any one singly. Figure 157 is an illustration of a small bank of dimmers.
Door Switches
Door Switches.—Door switches are used mostly in connection with dressing rooms. When the light in the room is burning, opening and closing the door will turn it out.
Dressing Rooms
Dressing Rooms.—Many dressing rooms are wired with lights on pendant cords, but this method is not to be recommended. It is better to arrange the lights in sockets fitted into the outlet boxes. It will be well if each dressing room is provided with a circuit for flatirons. If this is considered too expensive, the fuses on circuits leading into dressing rooms must be kept small enough to blow in case a flatiron is connected. Many actors are in the habit of carrying flatirons and will use them on incandescent-light circuits if no other circuit is provided. If metal guards are fastened on securely, much of the trouble from flatirons will be avoided, but they must be fastened so that an ordinary screwdriver will not loosen the screws.
Dressing room illumination, if properly carried out, will save the proprietor much annoyance. Actors have ways of obtaining the light they want by fair means or foul, and it is much better to arrange the lighting so that it will be satisfactory to those using it, than to have it continually tampered with.
A bright illumination is essential for making up and both sides of the face should be fully illuminated. To accomplish this it is necessary to provide at least two lights for each mirror. Every lamp should be provided with a substantial guard which may be securely fastened to the outlet box. This is especially necessary if small candle power lamps are furnished. For, if the light furnished is insufficient, there will be strong efforts made to replace the small lamps by larger ones. Guards are also necessary as a protection against fire. Actors are in the habit of drying small articles of clothing on the lamps, and fires have been known to start from this cause. The guards on the lamps throw shadows on the faces of the actors, and for this reason are not liked. In order to avoid the shadows, frosted lamps may be used, or two lamps on each side of the mirror. One lamp will then illuminate the shadows caused by the other. Where there are long dressing tables, as in rooms occupied by the chorus, mirrors may be placed between each two lamps on each side of the table and the lamps staggered vertically. In this way each party will receive the benefit of at least four lamps and the shadows will be less noticeable.
The color value of the lamps used in dressing rooms should match that of the lamps used on the stage. Some stages, for instance, are illuminated by flaming arcs which may give an altogether different effect to a “make up” than the tungsten lamps, for instance.
Where there are a large number of sockets without lamps in them, it is advisable to close the socket by a fuse plug from which the fuse has been removed, or in some similar manner in order to avoid the chance of short circuits from hat pins or similar objects used in dressing rooms.
Drop Lights
Drop Lights.—Drop lights should be avoided as much as possible. Where they must be installed reinforced cord, armored cable, or flexible steel armored cord should be used.
Emergency Lighting
Emergency Lighting.—Every theater must have an emergency lighting system as outlined in the rules below. The object of this is to provide a double system of illumination so as to reduce the likelihood of the theater being left in total darkness. This is a frequent occurrence where the theater is supplied by an isolated plant, and may also occur where the supply is obtained from a large outside lighting system although the latter is usually more reliable.
Every unnecessary light that is added to an emergency system increases the likelihood of trouble. A sufficient number of lights added to it to illuminate the space used by the audience in getting out is, therefore, necessary but more than this is a detriment rather than a help. The practice of connecting all of the hall and lobby lights to the emergency system is to be condemned, since it defeats the purpose of the rule which provides a double illumination system for every part of the theater used by the audience. The two systems should be carried into the auditorium, all stairways, exits, and lobby clear to the street. They should, furthermore, be kept entirely separate, in separate conduits and using separate meters.
The rule does not specify the number of exit and emergency lights required. Good practice requires a light for every 400 square feet or so. If each of these outlets be fitted with a 50 watt lamp the illumination will interfere with many of the acts and so, smaller lamps are generally used. One emergency light for each 60 seats will fill the bill nicely.
Over each exit, an exit light must be provided, but as these exit lights are usually incased in ruby glass such as shown in Figure 158 they cannot be counted as giving any illumination. In many theaters gas is used for emergency and exit lighting and in many respects this seems to be a good practice. In some quarters, however, it is believed that a fire in the scenery of a theater might create such an air pressure in the building as to overcome the low gas pressure and thus put out the gas at the very time when it is most needed. The very best suggestion that can be made is that of a storage battery to supply the emergency system. Where alternating current is used this, however, introduces some complications and becomes quite expensive. Avoid the use of key sockets, fan motors, or any unnecessary device on emergency or exit light circuits.
National Electrical Code Rules for Services
Where supply may be obtained from two separate street mains, two separate and distinct services must be installed, one service to be of sufficient capacity to supply current for the entire equipment of theater, while the other service must be at least of sufficient capacity to supply current for all emergency lights. Where supply cannot be obtained from two separate sources, the feed for emergency lights must be taken from a point on the street side of main service fuses. By “emergency lights” are meant exit lights and all lights in lobbies, stairways, corridors, and other portions of theater to which the public have access, which are normally kept lighted during the performance. Where the source of supply is an isolated plant within the same building, an auxiliary service of at least sufficient capacity to supply all emergency lights must be installed from some outside source, or a suitable storage battery within the premises may be considered the equivalent of such service.
Exit lights must not have more than one set of fuses between same and service fuses. Exit lights and all lights in halls, corridors, or any other part of the building used by audience, except the general auditorium lighting, must be fed independently of the stage lighting, and must be controlled only from the lobby or other convenient place in front of the house. All fuses must be enclosed in approved cabinets.
Figure 159 shows a diagram of an emergency lighting system together with that of the house lighting system. The main house switch is sometimes arranged with two sets of fuses, so that it need only be thrown over when a fuse blows. See Figure 159 at the right.
Exit Lights
Exit Lights.—Exit lights are usually required over all doors leading from any part of the auditorium to the lobby or outside of the theater. They are usually incased in ruby glass on which the word EXIT has been etched in large letters. See also Emergency Lighting.
Fan Motors
Fan Motors.—In large theaters, sometimes as many as ten or twelve fan motors are arranged along the walls of the auditorium, to blow air toward the audience. In small theaters there is a strong temptation to connect these to the emergency circuit, but this should never be done. The motors are too noisy to be allowed to run during an act and must be wired so that they can all be thrown on or off together from the stage switchboard. Not more than 660 watts should be connected to any one circuit and the connection should be by means of attachment plugs and reinforced cord, a bracket for the motor being placed as near as possible to the outlet, so as to reduce the amount of cord required to a minimum.
Fire Alarm
Fire Alarm.—In some of the cities a special signal system between stage and box office is required and it is necessary to consult authorities about this. Ordinarily a bell circuit, such as shown under “Bells,” will answer.
Fish Work
Fish Work.—The fishing of wires incased in loom, as is permitted in other places, is not permissible in theaters. If wires are to be “fished” they must be incased in metal armor.
Fixtures
Fixtures.—Fixtures require careful inspection before installing. It is seldom that the piping is properly reamed out as required by the rule. Chain fixtures especially, must be closely watched. There is little if any trouble to be expected from the wires laced among the chain links, but there is much trouble to be looked for from the wires at the points where they leave the chain support and where they enter the socket. The openings for the wires at these points are seldom large enough to admit of the proper wire being used, and they are not well reamed either. The result of these conditions is that the wire is very quickly abraded and short circuits are common.
Fixtures may be tested for short circuit by connecting a magneto at the feed end of the wires and turning it briskly. If a ring is obtained it is an indication that something in wrong. The test for open circuit may be made with the same connection. Insert a screw driver or a plug into each socket; if it is not possible to obtain a ring there must be an open circuit. The test for “ground” may be made by connecting both feed wires to one pole of the magneto, and the other pole to the metal of the fixture taking care that there is no lacquer on that part of the fixture. If a ring is obtained it is an indication that some bare spot on the wire is in contact with the fixture. Fixtures used for emergency lighting must carry no key sockets and must not feed fan motors.
National Electrical Code Rules for Fixture Wire and Fixtures
Wires for Fixture Work
Must not be smaller than No. 18 B. & S. gauge, and must have an approved rubber insulating covering. In wiring certain designs of show-case fixtures, ceiling bull-eyes, and similar appliances in which the wiring is exposed to temperature in excess of 120 degrees Fahrenheit (49 degrees centigrade), from the heat of the lamps, approved slow-burning wire must be used. All such forms of fixtures must be submitted for examination, test and approval before being introduced for use.
Supply conductors, and especially the splices to fixture wires, must be kept clear of the grounded part of gas pipes, and, where shells or outlet boxes are used, they must be made sufficiently large to allow the fulfillment of this requirement.
Must, when fixtures are wired outside, be so secured as not to be cut or abraded by the pressure of the fastenings or motion of the fixture.
Wires of different systems must never be contained in or attached to the same fixture, and under no circumstances must there be a difference of potential of more than 300 volts between wires contained in or attached to the same fixtures.
On chains of similar parts where conductors are not completely enclosed in metal, wires must be stranded and must have rubber insulation not less than one thirty-second of an inch in thickness; or approved pendant or portable cord may be used.
Fixtures
When supported at outlets in metal conduit, armored cable, or metal-molding systems, or from gas piping or any grounded metal work, or when installed on metal walls or ceilings, or on plaster walls or ceilings containing metal lath, or on walls or ceilings in fireproof buildings, fixtures must be insulated from such supports by approved insulating joints placed as close as possible to the ceilings or walls. The insulating joint may be omitted in conduit, armored cable, or metal-molding systems with straight electric fixtures in which the insulation of conductors is the equivalent of insulation in other parts of the system, and provided that approved sockets, receptacles, or wireless clusters are used of a type having porcelain or equivalent insulation between live metal parts and outer metal shells, if any.
Where insulating joints are required, fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings, or from plaster walls or ceilings on metal lathing, and from outlet boxes.
Canopy insulators must be securely fastened in place so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated.
Fixtures having so-called flat canopies, tops, or backs, will not be approved for installation, except where outlet boxes are used.
In non-metallic fixtures wireways must be metal-lined unless approved armored conductors with suitable fittings are used.
Flashers
Flashers.—Flashers are used to economize electrical energy in sign illumination. An electric sign is often just as effective if only one side or one letter is in use at a time and in such a case there is considerable saving by the use of a flasher.
Flashers are made up in a variety of forms, one of them being shown in Figure 160. The manner of wiring to the sign will be readily understood by reference to the figure. The neutral wire is carried direct to the sign and fuses for that wire are often installed up in the sign, while those for the other side of the circuits must be close to the flasher to comply with the rule which requires fuse protection where a small wire is tapped off from a larger one, unless the fuse in the larger wire is below the carrying capacity of the smaller.
National Electrical Code Rule for Flashers
Time switches, sign flashers, and similar appliances must be of approved design and enclosed in approved cabinets.
Flat Irons
Flat Irons.—See Heaters.
Flexible Cord
Flexible Cord.—The ordinary flexible cord should not be used in any part of a theater. It is recommended that only those cords described below be used, each of course in its proper place. Approved reinforced cord for pendants. Approved asbestos-covered cord for portable heaters. Approved Stage and Border Cables on Stage.
See “Stage Cables.”
Flexible Tubing
Flexible Tubing.—Flexible tubing is not permissible in theaters.
Floor Pockets
Floor Pockets.—These are always a source of trouble and their use should be avoided as much as possible. If it is necessary to use any they must be of a type approved by the inspection department having jurisdiction.
Fly Floor
Fly Floor.—This is the name given to that part of the gallery above the stage upon which those employes, whose duty it is to raise and lower curtains and scenery, work. No great illumination is required, but the lights should be arranged so as to be convenient to the men for reading during long waits. If this is not done there will always be considerable objectionable cord wiring found in this place. Fly-floor and rigging-loft lights should be provided with three way switches so that lights may be turned on or off either at the stage switchboard or on the fly floor.
Footlights
Footlights.—These form the most important and effective part of the permanently located stage lights. To locate them properly requires careful consideration. If they are brought too high they will obstruct the view of the audience; if located too low they will not illuminate the lower part of the stage.
Opinion is somewhat divided as to whether they ought to be arranged in circular form or be laid out straight across the stage. In large theaters there is a circular space between the front seats and the front of the stage. A circular stage will utilize this space and this form of stage with footlights arranged in a similar manner will also allow the actors to approach more closely to the audience and will procure for them some illumination from the side. The difficulty of making up a circular strip of footlights is somewhat greater than that of making them up in a straight line.
The footlights are generally made to extend nearly the full opening of the stage and the lights should be crowded into them as closely as possible. The lighting should be divided into three groups suitable for three colors. It is customary to have about half of the lights white and the remaining half divided into two equal parts for different colors. A small part of the white lights should be arranged upon a separate circuit so that they may be used for rehearsals or other purposes, when not very much light is needed.
No very definite recommendations concerning the type of lamp to be used can be given. In some theaters the stage is very solid and tungsten lamps are used to advantage; in others the jarring prevents their use. The white lights should be arranged so that their light need not pass through the colored lamps. In vaudeville houses some protection in the form of chains or guards is often provided to prevent objects from being rolled or thrown against the lights. Figures 161 and 162 show types of footlights and the manner of installing the sockets.
The National Electrical Code Rules for Wiring Footlights
Must be wired in approved conduit or armored cable, each lamp receptacle being enclosed within an approved outlet box, or the lamp receptacles may be mounted in an iron or steel box, metal to be of a thickness not less than No. 20 U. S. sheet metal gauge treated to prevent oxidation and so constructed as to enclose all the wires. Wires to be soldered to lugs of receptacles. Must be so wired that no set of lamps requiring more than 1,320 watts nor more than 26 receptacles shall be dependent upon one cut-out.
Fuses
Fuses.—See “Cut-outs.”
Gallery Lighting
Gallery Lighting.—The proper lighting of galleries is a difficult matter where there is another gallery above. In such a case the ceiling is always very low. An even distribution of light requires the use of many small incandescent lamps evenly distributed. This will make the wiring expensive. The light should be taken pretty well from the rear so as to avoid placing lights in the range of visions of the audience. Emergency lights should be provided here as well as in the main auditorium.
Gallery Pockets
Gallery Pockets.—Pockets for arc lamps are often provided, as it often happens that a moving-picture machine must be placed in the gallery. The stage pockets should be wired with number 6 B. & S. gauge wire, this being the smallest wire allowed to feed a moving-picture arc. The stage pocket should be controlled by a switch on the switchboard. It often happens that the operator at the lamp has a wrong cue and his light can then be controlled by the stage manager at the stage switchboard.
Gas Lighting
Gas Lighting.—Electric gas lighting is very little used at the present time, but in many theaters the emergency lighting is by gas and, in order to save the time necessary to light these by hand before every performance, an automatic gas lighting system has been installed in some theaters. A diagram of such a system is shown in Figure 163. A battery of considerable capacity is necessary and also a spark coil S. At each gas jet a magnet M is installed which, when energized, is capable of turning the gas on and at the same time producing a spark. This magnet is also capable of turning the gas off. Two buttons are provided, one to turn the gas on and the other to turn it off.
As the wiring is always used in connection with gas piping, grounds are of frequent occurrence, and in order to indicate a ground as soon as it comes on, the bell and battery shown are provided. If a ground causes a continuous current, the spark coil will attract the armature, thus causing the bell to ring continuously.
National Electrical Code Rule for Gas Lighting
Electric gas lighting, unless it is the frictional system, must not be used on the same fixtures with the electric light.
Grid Floor
Grid Floor.—This is the term given to the framework which supports the pulleys over which the cables for handling curtains and scenery run. It is usually made up of parallel iron slats or bars; hence the name. A fairly good illumination should be provided here and all of the lights should be arranged on three-way switches. One light for every 400 square feet will be sufficient.
National Electrical Code Rule for Ground Clamps
Connections to grounded pipes and to conduit must be exposed to view or be readily accessible, and must be made by means of approved ground clamps to which the ground wire must be soldered.
National Electrical Code Rule for Grounding
The metal of conduit, armored cable, or metal molding must be permanently and effectually grounded to water piping, gas piping, or other suitable grounds, provided that, when connections are made to gas piping, they must be on the street side of the meter. If the conduit system consists of several separate sections, the sections must be bonded to each other, and the system grounded; or each section may be separately grounded, as required above.
Conduits and gas pipes must be securely fastened in outlet boxes, junction boxes, and cabinets, so as to secure good electrical connections.
If conduit, couplings, outlet boxes, junction boxes, cabinets, or fittings, having protective coating of non-conducting material such as enamel, are used, such coating must be thoroughly removed from threads of both couplings and conduit and such surfaces of boxes, cabinets and fittings where the conduit or ground clamp is secured in order to obtain the requisite good connection. Grounded pipes must be cleaned of rust, scale, etc., at place of attachment of ground clamp.
Connections to grounded pipes and to conduit must be exposed to view or readily accessible, and must be made by means of approved ground clamps to which the ground wires must be soldered.
Ground wires must be of copper, at least No. 10 B. & S. gauge (where largest wire contained in conduit is not greater than No. 0 B. & S. gauge), and need not be greater than No. 4 B. & S. gauge (where largest wire contained in conduit is greater than No. 0 B. & S. gauge). They shall be protected from mechanical injury.
The ground on the conduit system is not to be considered as a ground for a secondary system.
Guards
Guards.—A guard rail should be provided around the stage switchboard to prevent actors from coming in contact with any live part of the switchboard. All incandescent lamps about the stage, dressing rooms, fly-floor, grid-floor, etc., should be provided with guards.
Hanger-Boards
Hanger-Boards.—Hanger-boards are not compulsory but where not used, arc lamps must be hung from insulating supports other than their conductors.
National Electrical Code Rule for Hanger-Boards for Series Arc Lamps
Hanger-boards must be so constructed that all wires and current-carrying devices thereon will be exposed to view and thoroughly insulated by being mounted on a non-combustible, non-absorptive, insulating substance. All switches attached to the same must be so constructed that they shall be automatic in their action, cutting off both poles to the lamps, not stopping between points when started, and preventing an arc between points under all circumstances.
Heaters
Heaters.—Heaters are used sometimes in cold dressing rooms, in box offices and in other small spaces where other adequate heating arrangements have not been made. The fire hazard incident to the use of electric heaters is considerable and they should be carefully installed according to the rules given below.
From one-half to three watts per cubic foot will be required to heat a room. The quantity of heat necessary to be supplied depends largely upon the ventilation. It will be small in closed dressing rooms and large, for instance, in the box office. Always place a heater where the air enters a room; never where it leaves.
National Electrical Code Rules for Electric Heaters
Each heater of more than 6 amperes or 660 watts capacity must be protected by a cut-out, and controlled by a switch or plug connector plainly indicating whether “on” or “off” and located within sight of the heater. Heaters of 6 amperes or 660 watts capacity, or less, may be grouped under the protection of a single set of fuses, provided the rated capacity of the fuses does not exceed 10 amperes; or may be connected individually to lighting circuits.
Flexible conductors for smoothing irons and sad irons, and for all devices requiring over 250 watts, must have an approved insulation and covering.
With portable heating devices, approved plug connectors must be used so arranged that the plug may be pulled out to open the circuit without leaving any live parts so exposed as to render likely accidental contact therewith. The connector may be located at either end of the flexible conductor or inserted in the conductor itself.
Smoothing irons, sad irons, and other heating devices that are intended to be applied to combustible articles, must be provided with approved stands.
Stationary heaters such as radiators, ranges, plate warmers, etc., must be so located as to furnish ample protection between the device and surrounding combustible material.
Must each be provided with a name-plate, giving the maker’s name and the normal capacity in volts and amperes.
High Potential
High Potential.—The National Electrical Code classifies all voltages below 550 as low. Nevertheless voltages above 220 should not be considered in the auditorium, stage, or dressing rooms of any theater. And this voltage only in connection with a three-wire system where the high voltage exists only between the outside wires, and 110 volts are used for lamps and other devices. High potential systems should be used only on the outside.
Illumination
Illumination.—Illumination is more an art than a science and the rules that can be given have only a very general application. The best practice, where really good illumination is desired, is to install a large number of circuits in proportion to the number of lights, so that lamps of large candle power may be used wherever desirable. The quantity of light needed in theaters varies greatly with the color of decorations and with their condition. Dust accumulates rapidly in theaters and may absorb half of the light. If there is plenty of capacity the candle power of lamps may be changed to suit conditions and obtain any result desired.
The number of sockets installed in the auditorium varies widely. In some of the cheaper theaters one light for each twenty seats is considered sufficient; while in elaborately lighted houses, there are cases where the number of sockets is equal to about half the number of seats. Good illumination requires that the light come from the back, but very often the purpose is to obtain a brilliant effect by placing lights in front of the audience. In such cases, however, the lamps are always of low candle power and should be frosted.
Incandescent Lamps
Incandescent Lamps.—Practically all incandescent lamps are now rated in watts. They can be obtained in voltages ranging from 2 to 250 and may be operated in series or in multiple. All but the tantalum lamp operates equally well on alternating or direct current. The tantalum cannot be recommended for alternating-current circuits. No incandescent lamps will operate well on frequencies lower than forty cycles. The natural distribution of light is mostly in the horizontal plane and for good illumination reflectors should be provided.
The color value is in the following order: Tungsten, tantalum, graphitized filament, carbon filament. None are equal for color-matching purposes to the intensified arc or the Moore tube.
The life of all incandescent lamps varies inversely with the voltage. An increase in voltage will produce an increase in the efficiency of the lamp but shorten its life. The efficiency decreases with continued use, and it is generally considered that the useful life of a lamp is over when its efficiency has fallen to 80 per cent of its original value. Frosting or coloring shortens the life of lamps from 30 to 50 per cent and reduces the candle power from 3 to 10 per cent, but the lamp yields a more pleasing light. Frosting is ordinarily used only where lamps are placed so as to come in the line of vision. Bowl frosting does not materially reduce the life of a lamp.
Efficiency of Lamps
With incandescent lamps the term “efficiency” has a meaning quite different from that usually given, it being the number of watts per candle power. The lower the efficiency of an incandescent lamp, the better it is and the more light it yields per watt consumed.
Mazda Lamp
The Mazda lamp has an efficiency of about 1.25 and is the most efficient of all. It may be recommended in all places where lamps may be suspended vertically; where there is not too much jarring; where there is ordinary care in handling; and where the lamps are burning a large part of the time. The operating expense of this lamp is low, but the initial cost is high and the breakage is likely to be considerable. If lamps are much handled and not burned much, the cost of broken lamps may exceed the saving in energy. It is best not to clean Mazda lamps when cold. Shock absorbers should be used where there is much jarring. The illumination should be laid out for the use of lamps not smaller than 60 watts. The lamps should not be used for temporary work or for coloring. Arrange lamps as far as possible to be controlled by switches. Broken filaments can often be united again by shaking the lamps gently until the broken ends come together. The current will then weld them. When a bank of Mazda lamps is turned on there is an excessive current for an instant.
Tantalum Lamp
The efficiency of this lamp is from 1.8 to 2 watts per candle power. This lamp is much used for street-car and similar illumination because it stands jarring very well. It should not be used on alternating-current circuits. The filament can often be united in the same manner as the Mazda.
Graphitized Filament Lamp
This lamp has an efficiency of 2.5 watts per candle power.
Carbon Filament Lamp
This lamp used on 110-volt circuits has an efficiency of from 3 to 3.2 watts per candle power. The efficiency of the smaller sizes is from 4 to 5 watts per candle power. The carbon filament lamp is the most expensive of all to operate, but on account of the strength and cheapness of the lamp it can be recommended in places where the breakage is liable to be great or where the light is used for comparatively brief periods.
National Electrical Code Rules for Incandescent Lamps
Must be provided with guards when liable to come in contact with inflammable material or subject to rough usage. Must be protected by vapor-proof globes where inflammable gases exist.
National Electrical Code Rules for Insulating Joints
When supported at outlets in metal conduit, armored cable, or metal molding systems, or from gas piping or any grounded metal work; or when installed on metal walls or ceilings, or on plaster walls or ceilings containing metal lath, or on walls or ceilings in fireproof buildings, fixtures must be insulated from such supports by approved insulating joints placed as close as possible to the ceilings or walls. The insulating joint may be omitted in conduit, armored cable, or metal molding systems with straight electric fixtures in which the insulation of conductors is the equivalent to insulation in other parts of the system, and provided that approved sockets, receptacles, or wireless clusters are used of a type having porcelain or equivalent insulation between live metal parts and outer metal shells, if any.
Where insulating joints are required, fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings, or from plaster walls or ceilings on metal lathing, and from outlet boxes.
Canopy insulators must be securely fastened in place, so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated.
Inverted Lighting
Inverted Lighting.—In this method of lighting the light is first thrown upward against the ceiling and then reflected back. This method can be used to advantage with light colored ceilings only. It is especially suited for low ceilings and with high ceilings the advantage disappears. The light obtained in this manner is very even and almost shadowless. Much light is lost through absorption but, owing to the fact that the light is of such an even quality, the eye readily accommodates itself to a lower quantity and the net increase in energy required to illuminate suitable spaces is not so very great. Those who wish to go into the subject of illumination thoroughly will find it treated fully in “Modern Illumination Theory and Practice”.
Joints
Joints.—Methods of making joints are illustrated in Figure 164. Be careful not to overheat, especially at points where there is a strain on the wire.
National Electrical Code Rule for Joints.
Wires must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must then be soldered unless made with some form of approved splicing device, and covered with an insulation equal to that on the conductors.
Stranded wires (except in flexible cords) must be soldered before being fastened under clamps or binding screws; and, whether stranded or solid, when they have a conductivity greater than that of No. 8 B. & S. gauge they must be soldered into lugs for all terminal connections, except where an approved solderless terminal connector is used.
Junction Boxes
Junction Boxes.—Junction boxes are installed in conduit systems for the purpose of facilitating the drawing in of the wire or of branching off from a main run. See “Conduit Work.”
Lamps
Lamps.—See “Incandescent Lamps.”
Lobby
Lobby.—The lobby generally requires a number of lights and the aim often is to create a lavish display. Very often a cut-out center is arranged at some convenient place. The exit and emergency lights must be controlled from the lobby. Sometimes outlets are provided for electric bulletin boards or small signs.
Lugs
Lugs.—For solderless lugs, such as are used on rheostats or for arc lamps, see “Portable Stage Equipment.”
National Electrical Code Rule for Lugs.
For fuses rated over 30 amperes lugs, firmly screwed or bolted to the terminals and into which the conducting wires are soldered, must be used. On rheostats, resistances, etc., lugs will not be required when leads are provided as a part of the device.
Switches for current of over 30 amperes must be equipped with lugs, firmly screwed or bolted to the switch, and into which the conducting wires shall be soldered. For the smaller sized switches simple clamps can be employed, provided they are heavy enough to stand considerable hard usage.
Where lugs are not provided, a rugged double-V groove clamp is advised. A set screw gives a contact at only one point, is more likely to become loosened, and is almost sure to cut into the wire. For the smaller sizes, a screw and washer connection with up-turned lugs on the switch terminal gives a satisfactory contact.
National Electrical Code Rules for Metal Moldings
Must not be used on stage side of proscenium wall.
Must not be used for circuits carrying more than 1,320 watts.
Wire used must be standard rubber covered, but may be single braid.
Must never be concealed or run in damp places.
Must not be used where the difference of potential exceeds 300 volts.
Must be continuous from outlet to outlet, to junction boxes, or approved fittings designed especially for use with metal moldings, and must at all outlets be provided with approved terminal fittings which will protect the insulation of conductors from abrasion, unless such protection is afforded by the construction of the boxes or fittings.
Such molding where passing through a floor must be carried through an iron pipe extending from the ceiling below to a point five feet above the floor, which will serve as an additional mechanical protection and exclude the presence of moisture often prevalent in such locations.
Where the mechanical strength of the molding itself is adequate, this ruling may be modified to require the protecting piping from the ceiling below to a point at least three inches above the flooring.
Where such moldings pass through a partition the iron pipe, required for passing through floors, may be omitted and the molding passed directly through, providing the partition is dry and the molding is in a continuous length with no joint or coupling within the partition.
Backing must be secured in position by screws or bolts, the heads of which must be flush with the metal.
Must have the metal of molding permanently and effectually grounded to water piping, gas piping, or other suitable grounds, provided that when connections are made to gas piping, they must be on the street side of the meter. If the metal molding system consists of several separate sections, the sections must be bonded to each other and the system grounded, or each section may be separately grounded, as required above.
Metal moldings and gas pipes must be securely fastened to outlet boxes, junction boxes, and cabinets, so as to secure a good electrical connection. Molding must be so installed that adjacent lengths of molding will be mechanically and electrically secured at all points.
If metal molding, couplings, outlet boxes, junction boxes, cabinets, or fittings having protective coating of non-conducting material such as enamel are used, such coating must be thoroughly removed from threads of couplings and metal moldings, and from the surfaces of boxes, cabinets, and fittings, where the metal molding or ground clamp is secured in order to obtain the requisite good connection. Grounded pipes must be cleaned of rust, scale, etc., at the place of attachment of the ground clamp.
Connection to grounded pipes and to metal moldings must be exposed to view, or readily accessible, and must be made by means of approved ground clamps, to which the wires must be soldered.
Ground wires must be of copper, at least No. 10 B. & S. gauge. They shall be protected from mechanical injury.
Must be installed so that for alternating-current systems the two or more wires of a circuit will be in the same metal molding. It is suggested that this be done for direct-current systems also so that they may be changed to the alternating-current system at any time, induction troubles preventing such change if the wires are in separate moldings.
Meters
Meters.—A good job of meter setting requires that the meter fittings which are now on the market be used. Two separate meters will be required in each theater; one for the general lighting and one for the emergency system.
Meter Reading
Meter Reading.—Meter readings are indicated by pointers, arranged to move over dials as shown in Figure 165. The various pointers are connected together by gearing in such a manner, that alternate pointers move in opposite directions, as indicated by the figures on the dials. The gearing moving the pointers in Figure 165 is of such proportions that a total revolution of any pointer represents one-tenth of a revolution of the pointer to the left of it. Thus ten revolutions of one pointer causes one revolution of the one at the left.
At the top of each dial the value of the reading of that dial is shown. Where the figures given are followed by the letter “s”, as in Figures 167 and 168, it signifies that each division of the dial represents the amount of energy indicated by the figures at the top. For instance, in Figure 168 each division of the dial at the right represents one-tenth of one kilowatt hour and a total revolution of the pointer ten-tenths, or one kilowatt hour.
If the figures given at the top of the dial are not followed by the letter “s”, or as shown in Figure 166, each division of the dial represents one-tenth of the amount shown at the top of the dial, the dial at the right of Figure 166 indicating nine-tenths of ten kilowatts or nine kilowatts.
The meter must always be read from right to left, the lowest indicating dial being the one at the extreme right, and the lower reading ones always being used to check the higher ones just at the left. The following example will illustrate the manner of reading meters:
In Figure 165 the right-hand pointer registers nine-tenths of 1000, or 900 watt hours; the pointer next to it registers eight, since it cannot be considered as fully up to any number unless the pointer at the right of it has just arrived at or passed 0. By the same token the middle pointer also registers 8 and as the middle pointer has not reached 0 the one at the left of it must be read as one, the last dial also indicates one and the total reading is 1,188,900. On some types of meters a multiplier is used. This is generally given on the meter dial and the readings given by the pointers must be multiplied by this number to obtain the correct reading of the meter.
Motors
Motors.—Motors are used in theaters for ventilation, for raising and lowering the steel curtain in cities where such are required, and also in some cases for operating drop curtains, but for this last purpose they have not found much favor. In some localities motors are required to keep up a certain water pressure to be used in case of fire. Voltages higher than 550 are not considered in theater work.
National Electrical Code Rules for 550-volt Motors and Less
Motors operating at a potential of 550 volts or less must be thoroughly insulated from the ground wherever feasible. Wooden base frames used for this purpose, and wooden floors, which are depended upon for insulation where, for any reason, it is necessary to omit the base frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry. Where frame insulation is impracticable special permission in writing may be given for its omission, in which case the frame must be permanently and effectively grounded.
The motor leads or branch circuits must be designed to carry a current at least 25 per cent greater than that for which the motor is rated. Where the wires under this rule would be over-fused in order to provide for the starting current, as in the case of many of the alternating-current motors, the wires must be of such size as to be properly protected by these larger fuses.
Each motor and resistance box must be protected by a cut-out and controlled by a switch; said switch plainly indicating whether “on” or “off”.
Small motors may be grouped under the protection of a single set of fuses, provided the rated capacity of the fuses does not exceed 6 amperes. With motors of one-fourth horse power or less, on circuits where the voltage does not exceed 300, single-pole switches may be used. The switch and rheostat must be located within sight of the motor, except in cases where special permission to locate them elsewhere is given, in writing.
Where the circuit-breaking device on the motor-starting rheostat disconnects all wires of the circuit, the switch called for in this section may be omitted. Overload-release devices on motor-starting rheostats will not be considered to take the place of the cut-out required by this section. An automatic circuit-breaker disconnecting all wires of the circuit may serve as both switch and cut-out.
Auto starters, unless equipped with tight casings enclosing all current-carrying parts, in all wet, dusty, or linty places, must be enclosed in dust-tight, fireproof cabinets. Where there is any liability of short circuits across their exposed live parts being caused by accidental contacts, a railing must be erected around them.
Must not be run in series-multiple or multiple-series, except on constant-potential systems, and then only by special permission.
Must, when combined with ceiling fans, be hung from insulated hooks, or else there must be an insulator interposed between the motor and its support.
Must each be provided with a name-plate, giving the maker’s name, the capacity in volts and amperes, and the normal speed in revolutions per minute.
All varying (or variable) speed alternating-current motors except those used for railway service must be marked with the maximum current which they can safely carry for 30 minutes, starting cold.
Terminal blocks when used on motors must be made of approved non-combustible, non-absorptive, insulating material such as slate, marble, or porcelain.
Adjustable-speed motors, unless of special and appropriate design, if controlled by means of field regulation, must be so arranged and connected that they cannot be started under weakened field.
The use of soft rubber bushings to protect the lead wires coming through the frames of motors is permitted, except when installed where oils, grease, oily vapors, or other substances known to have rapid deleterious effect on rubber are present in such quantities and in such proximity to motors as may cause such bushings to be liable to rapid destruction. In such cases hardwood properly filled, or preferably porcelain or micanite bushings must be used.
The following table shows the sizes of wire recommended to be used with motors of the horsepower given. This table is an extract from the rules of the Department of Gas and Electricity of the City of Chicago. The column headed “Mains” may be used when there are a number of motors fed by a single line. For all lines which supply a single motor only, the column headed “Branches” must be used.
The difference between the two is due to the fact that it is not believed that several motors fed by a single line will all be started at the same time; hence it is not necessary to provide the overload capacity for all of the motors as it is where but a single motor is installed.
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