Motion Picture Operation, Stage Electrics and Illusions / A Practical Hand-book and Guide for Theater Electricians, Motion Picture Operators and Managers of Theaters and Productions

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.

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:

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.

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”.

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: