Motion Picture Operation, Stage Electrics and Illusions

Chapter XVIII: Theater Wiring (3)

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For 250 volts, boards, or blocks with the ordinary front-connected terminals, except where these have a mass of compact form equivalent to the back-connected terminals usually found in switchboard work, a substantial barrier of insulating material, not less than one-eighth of an inch in thickness, must be placed in the “break” gap--this barrier to extend out from the base at least one-eighth of an inch farther than any bare live part of the fuse-block terminal, including binding screws, nuts and the like.

For three-wire systems cut-outs must have the break-distance required for circuits of the potential of the outside wires.

TABLE X.

FUSE SPACINGS.

_Switch Spacings and Dimensions._

When designed with 250-volt spacings between adjacent blades, triple-pole switches must be marked 250 volts and may be used on 3-wire D. C. or single-phase systems having not more than 250 volts between adjacent wires and not more than 500 volts between the two outside wires.

Spacings and dimensions must be at least as great as those given below:

TABLE XI A.

SWITCH SPACINGS AND DIMENSIONS FOR SWITCH-BOARDS AND PANEL BOARDS.

TABLE XI B.

SWITCH SPACINGS AND DIMENSIONS FOR INDIVIDUAL SWITCHES.

_Not Over 125 Volts D. C. and A. C._

Inch Inch Inch Inch
30 amperes 1/2 by 5/64 1/2 by 3/64 1-1/4 1
60 and 100 amperes 1-1/2 1-1/4
200 amperes 2-1/4 2
400 and 600 amperes 2-3/4 2-1/2
800 and 1000 amperes 3 2-3/4

A 300-ampere switch with the spacings of the 200-ampere switch above may be used on switchboards.

TABLE XI C.

SWITCH SPACINGS AND DIMENSIONS FOR ALL SWITCHES.

_250 Volts Only D. C. and A. C._

Inch Inch Inch Inch
30 amperes 1/2 by 5/64 1/2 by 3/64 1-3/4 1-1/2

TABLE XI D.

SWITCH SPACINGS AND DIMENSIONS FOR ALL SWITCHES.

_Not Over 250 Volts D. C. nor Over 500 Volts A. C._

Inch Inch Inch Inch
30 amperes 5/8 by 1/8 5/8 by 1/16 2-1/4 2
60 and 100 amperes 2-1/4 2
200 amperes 2-1/2 2-1/4
400 and 600 amperes 2-3/4 2-1/2
800 and 1000 amperes 3 2-3/4

A 300-ampere switch with the spacings of the 200-ampere switch above may be used on switchboards.

Cut-out terminals on switches for over 250 volts must be designed and spaced for 600-volt fuses.

TABLE XI E.

SWITCH SPACINGS AND DIMENSIONS FOR ALL SWITCHES.

_Not Over 600 Volts D. C. and A. C._

Inch Inch Inch Inch
30 amperes 5/8 by 1/8 5/8 by 1/16 4 3-1/2
60 amperes 4 3-1/2
100 amperes 4-1/2 4

_Paint Bridge._--The paint bridge is usually a scaffold which can be raised and lowered, and which serves the purpose of carrying scene painters at work on the curtains. A long strip is the best means of illumination and it must be connected with long stage cable so as to be portable.

_Paint Room._--Rooms in which paints are stored should not contain switches or cut-outs. Lamps should be incased in vapor-tight globes.

_Program Board._--A simple form of program board is shown in Figure 169. Except at the top and the bottom, where three lamps are shown together in one compartment, each lamp is incased by itself. In front of the lamps is usually colored glass, bearing numbers or letters. The lamp behind any number being turned on, that number becomes visible. The top and bottom are usually labeled, “Special”, or “Extra”.

Another form of program board is shown in Figure 170. This requires much more wiring. Each lamp on the board is connected to a plug or switch at the operator’s station. Whichever switch is closed on the small board at the right causes a corresponding light on the large board to appear.

Two program boards are usually installed, one at each side of the stage, facing the audience at angles, so that one can be seen from the extreme right, the other from the extreme left.

A system that is often used for carriage call is shown in Figure 171. The lights are arranged on circuits as indicated by numbers. All lamps bearing the same number being connected to one wire leading to the controlling station. Thus there are eight controlling or switch wires and there is one wire common to all. A special switch is provided which has a contact point for each wire. Paper cards, perforated specially for the numbers they represent, are used. If a card bearing a certain number is inserted in the proper place and the switch closed, the number printed on the card will appear on the sign. If, for instance, the shaded circles in the card at the left of the figure allow contact to be made, the lights indicated by black circles will light up and make the figure “6”.

Another form of program or call board is shown in Figure 172. This requires more wires than the one just described, one wire being carried to the controlling board from each lamp. The connections may be made in various ways. Sometimes they are made with knife switches. If it is desired to make the figure 1, for instance, only the three lights in a vertical row in the center need be lighted, and to do this the three wires from those lamps must be connected to one switch. To make the figure 2, seven lamps would have to be lit by another switch. It is capable of making any letter or number and when used as a program board only may be somewhat simplified.

In connection with these signs a large number of wires may be required and attention should be given to the following rule:

_National Electrical Code Rule for Wiring Program and Call Boards._

Except in the case of stage pockets the same conduit must never 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.

_Proscenium Side Lights._--These lights are located on each side of the stage, as near as possible to the edge of the proscenium opening and often in front of the steel curtain. They are of more use in musical productions, where choruses spread over the whole stage, than in dramatic productions where the interest is more in the center of the stage. In some theaters the proscenium side lights extend the full height of the opening and are arranged for three colors in the same manner as footlights and borders. Very often, however, only ten or twelve lights are arranged on each side of the stage.

The construction rules are the same as those governing foot-lights.

Lamps must be protected by strong wire mesh. This is essential as in many cases actors are very likely to back into them while passing off the stage. Portable strips are sometimes used as proscenium side lights.

_Receptacles._--See “Stage Pockets”.

_Retiring Rooms._--In these places a quiet subdued illumination is usually desired. There are also often quaint objects and effects to be illuminated. A large number of outlets conveniently located for the use of table lamps, fire places, and illumination of pictures, should be provided.

_Rheostats._

_National Electrical Code Rules for Rheostats._

_Location._

Must be placed on a switchboard, or at a distance of at least one foot from combustible material, or separated therefrom by a slab or panel of non-combustible, non-absorptive, insulating material such as slate, soapstone, or marble, somewhat larger than the rheostat, which must be secured in position independently of the rheostat supports. Bolts for supporting the rheostat shall be countersunk at least one-eighth inch below the surface at the back of the slab and the bolt heads shall be covered with insulating material. For proper mechanical strength, slab should be of a thickness consistent with the size and weight of the rheostat, and in no case to be less than one-half inch.

If resistance devices are installed in rooms where dust or combustible flyings would be liable to accumulate on them, they must be equipped with dust-proof face plates.

_Materials._

Must be made entirely of non-combustible materials, except such minor parts as handles, magnet insulation, etc. All segments, lever arms, etc., must be mounted on non-combustible, non-absorptive, insulating material.

_Connections._

Clamps for connecting wires to the terminals must be so designed as to insure a thoroughly good connection and must be sufficiently strong and heavy to withstand hard usage. 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.

_No-Voltage Release._

Motor-starting rheostats must be so designed that the contact arm cannot be left on intermediate segments, and for direct-current circuits must be provided with an automatic device which will interrupt the supply circuit before the speed of the motor falls to less than one-third of its normal value. In motor-starting rheostats for alternating-current circuits the automatic interrupting device may be omitted.

_Overload Release._

Overload-release devices which are inoperative during the process of starting a motor will not be approved, unless other circuit-breakers or fuses are installed in connection with them.

_Signals._--Signals are necessary between the manager’s office and the stage electrician’s station; for this purpose telephones are generally used. In many cities a fire-alarm signal system is also required and it is specified to what part of the house it shall lead. In addition to the above, a means of signalling the fly floor and the orchestra leader must be provided. Buzzers are used for these signals. It is best to use batteries for all these signals instead of attempting to run them from lighting circuits. Means of signalling the arc-lamp station in the gallery or the balcony should also be provided for use in connection with lantern slides, etc. Telephone connection to this point will also be very useful in order to give instructions to the lamp operator. Return-call systems are advisable in all places so that the electrician can be called from any point.

In some cities the local laws require these wires to be in conduit so as to preclude any possibility of their communicating fire to anything. At any rate the wires should be very carefully installed.

_Signs._--In nearly all electric signs used about theaters the letters are outlined by incandescent lamps. Small candle-power lamps are always used. They are not only economical but much more attractive because the glare from too much light is very annoying. Many signs are equipped with low candle-power tungsten lamps wired in series. In order that the letters should show to full advantage they should be glossy white and be kept clean. Such letters will show as bright as the lamps. It is best to wire the sign so that either side can be used independent of the other. In many cases, also, signs are wired so that each letter is independent of the others for use with flashers.

Attraction signs are used to advertise the attractions which appear from time to time. Independent portable letters are used and changed as often as the attractions change. Each letter must be fitted with cable and attachment plug of some kind and should have a separate circuit. Cut-outs are generally located on the frame and must be protected from the weather.

_Sockets._--Sockets must be of approved construction. Key sockets must not be used for emergency or exit lighting. Sockets with fiber linings must not be used unless protected by insulating joints. In damp places weatherproof sockets must be used. Where inflammable gases exist, lamps must be incased in vapor-proof globes. Porcelain sockets should not be used in theaters. Weatherproof sockets are generally used for portable purposes because they have no screws, etc., to work loose.

_Stage Cable._--Stage cables are allowed in theaters only where flexible conductors are absolutely necessary. All wiring that can possibly be installed in conduit or strip construction should be so arranged. By the use of plugging boxes the quantity of stage cable necessary can be much reduced. Plugs for arc and incandescent lights must not be interchangeable.

_Stage Flues._--In most cities stage flues, as described in the chapter on “Theater Buildings”, are required. The requirement is also, often, that they be released by electrical means. The rule below contemplates a circuit containing an electro-magnet and at least two switches in series. The magnet must be energized to hold the ventilator closed. If the current fails or a switch is opened the dampers must fly open at once. Where direct current is available the magnet is usually wound for 110 volts and connected to a circuit that is always alive. In case of an isolated plant which is shut down at night some arrangement for tying the dampers down should be made, but it is not always advisable, as once tied they are likely to remain so and sure to fail when needed. Magnets do not work well on alternating currents and in such cases the magnet should be wound for a small current to be obtained from a gravity battery which may be allowed to be always working. Locate the battery where it will not freeze.

_National Electrical Code Rules for Control of Stage Flues._

In cases where dampers are released by an electric device, the electric circuit operating same must be normally closed. Magnet operating dampers must be wound to take full voltage of circuit by which it is supplied, using no resistance device, and must not heat more than normal for apparatus of similar construction. It must be located in loft above scenery, and be installed in a suitable iron box with a tight, self-closing door.

Such dampers must be controlled by at least two standard single-pole switches mounted within approved iron boxes provided with self-closing doors without lock or latch, and located, one at the electrician’s station and the others as designated.

_Stage and Gallery Pockets._--Stage pockets are usually located on each side of the stage just far enough from the center to be safely back of the scenery. The more pockets there are the better it will be. Each pocket usually contains four circuits, and one of these at least should be for incandescent lights. It will be convenient if the stage pockets are divided into four groups, each group under control of a separate switch and the whole again under control of a main switch. This will enable the operator to throw off all of the pockets at once, if necessary, or to make any combination desired.

Sometimes lights fed through stage pockets require to be dimmed; but it is hardly practicable to arrange dimmers for apparatus carried by traveling companies, since a dimmer must be selected with respect to the amperage it is to control.

In addition to the rules given below, some cities require the bottom of stage pockets to be open, so as to avoid an accumulation of dust. This is a very essential precaution, as otherwise the pockets soon fill up or require very frequent cleaning. The covers must be substantial as heavy trucks are sometimes run over them. Two illustrations of stage pockets are given in Figures 173 and 174. The plugs used with these boxes are shown in Figure 175.

Gallery pockets are not usually laid in the floor but along the railing. The gallery pockets should be under separate control from the stage switchboard.

_National Electrical Code Rules for 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-ampere 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.

_Switches._--All knife switches should be enclosed in cabinets unless they are located on a switchboard. In exposed places, flush switches should be used. The usual height at which scattered switches are located is about four and one-half feet above floor. Door switches are of use principally in dressing rooms.

Diagrams of three-way switches are given in Figures 176 and 177. In Figure 177, the wiring by which a light can be controlled from three different points is shown. The middle switch must be a pole-changing switch. In this case a throw-over knife switch is wired to perform this function. Omitting the knife switch we have two three-way switches controlling the light. When both switches (indicated by broken lines) connect to the same wire the light burns.

In Figure 176, when both switches connect to the same polarity the light is out; when one of them is connected to the other pole the light burns. Under certain conditions this arrangement is more economical in wire but has the disadvantage which the other method avoids, of bringing both poles to each switch. This method cannot be used with direct-current arc lamps. Three-way switches are useful on stairways, enabling one to turn on a light at the bottom of the stairway and turn it off when at the top or vice versa.

_National Electrical Code Rules for Switches and Connections._

_Switches._

Must be placed on all service wires, either overhead or underground, in the nearest readily accessible place to the point where the wires enter the building, and arranged to cut off the entire current. Departure from this rule may be authorized only under special permission in writing. Switches controlling emergency lighting must be located only in the lobby.

Must when used for service switches, indicate, on inspection, whether the current be “on” or “off”. Switch cabinets must be deep enough to allow the door to be closed when 30 ampere branch-circuit switches are in any position, and when larger single-throw switches are thrown open as far as their construction and installation will permit.

Must, for constant-current systems, close the main circuit and disconnect the branch wires when turned “off”; must be so constructed that they shall be automatic in action, not stopping between points when started, and must prevent an arc between the points under all circumstances. They must indicate whether the current be “on” or “off”. Service cut-out and switch must be arranged to cut off current from all devices including meters.

Must always be placed in dry, accessible places, and be grouped as far as possible. Single-throw knife switches must be so placed that gravity will not tend to close them. Double-throw knife switches may be mounted so that the throw will be either vertical or horizontal as preferred, but if the throw be vertical a locking device must be provided, so constructed as to insure the blades remaining in the open position when so set.

When practicable switches must be so wired that blades will be “dead” when the switch is open.

When switches are used in rooms where combustible flyings would be likely to accumulate around them, they must be enclosed in dust-tight cabinets.

Up to 250 volts and thirty amperes, approved indicating snap switches are suggested in preference to knife switches on lighting circuits.

Single-pole switches must never be used as service switches nor for the control of outdoor signs or circuits located in damp places, nor placed in the neutral wire of a three-wire system, except in the two-wire branch or tap circuit supplying not more than 660 watts.

Where flush switches or receptacles are used, whether with conduit systems or not, they must be enclosed in an approved box constructed of iron or steel, in addition to the porcelain enclosure of the switch or receptacle.

Hinges of knife switches must not be used to carry current unless they are equipped with spring washers, held by lock-nuts or pins, or their equivalent, so arranged that a firm and secure connection will be maintained at all positions of the switch blades.

Spring washers must be of sufficient strength to take up any wear in the hinge and maintain a good contact at all times.

_Connections._

Switches for currents of over thirty amperes must be equipped with lugs, firmly screwed or bolted to the switch, and into which the conducting wire 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.

_Spacings._

See “Panel Boards”.

_Switchboards._--The stage switchboard is usually located on the right-hand side of the stage. This position enables the operator to watch cues easily and handle his switches with the right hand. This side is also the one from which the stage manager prefers to work. It is preferable to have the board raised high enough above stage level to allow all space on the stage to be used by actors. If the switchboard is located on stage level it takes up much room that is valuable and makes stage exits for actors difficult.

The wiring of a good switchboard should be divided into three parts, each part independent of the others, so that any one part can be entirely cut off without interfering with the other. All of the house lights should be fed through one main switch, and all of the stage light connected to another set of bus-bars, but it is best not to have the stage side of the board as a whole controlled by a main switch. If the stage side of the board is controlled by a single switch there exists the possibility that this switch may be used to cut off everything for a dark scene and when light is again wanted a part of the lighting of the previous setting may be left on and possibly interfere with the new scene.

The stage lighting is usually divided into four groups, viz.: three color groups and a group of stage pockets. The number of white lights is usually equal to that of all of the colors.

Figure 178 shows a well laid out switchboard. All of the lights in the auditorium are controlled by switches shown in the upper right-hand corner and all of these are under the control of the main switch. The house lights are usually thrown on or off as a whole and this main switch must be convenient for the operator.

The stage pockets are controlled by the bank of switches shown at _E_. Lights burning off the stage pockets generally are controlled by special operators on the stage or by actors, and need not be so very convenient to the switchboard operator. They must, however, be under his control when necessary; but here also a main switch is not advisable.

In addition to the three groups of lights spoken of above, there are a number of lights which should be controlled from the switchboard but must be so connected that they will be left on, no matter what is done with either house or stage light.

In this group belong a few lights mounted at the top of the switchboard which enable the operator to see his switches when all else is dark. These lights are generally shielded so as to throw no light in the direction of the stage opening. The orchestra lights also belong in this group, but a special switch may, with advantage, be arranged on this circuit to bring it under the control of one of the musicians. In some dark scenes these lights are turned out for a short time, but it is very important that they be turned on again at the proper moment, and this is more certainly assured, by giving the musicians control, than by leaving it to an electrician on the stage who may be very busy with other matters at the time.

The lights on the fly floor and in the rigging loft, as well as those in dressing rooms and basement, must also be independent. Fan motor circuits should also be independent of the house circuit. They are often needed when the house lights are thrown off.

With the switchboard illustrated in Figure 178 we have shown only the switches governing the house and stage proper. The switches governing the other lights are usually worked into the vacant spaces between the two groups. Each switch should be labeled in such a manner that a new operator can learn the board easily.

The most important part of the board is that part governing the stage lighting, and this should always be placed as conveniently as possible to the operator. A stage switchboard is like a house in that no one is wholly satisfied with the one he has, but thinks he could improve it a little if he could build it over again. The arrangement shown in Figure 178 is, however, quite satisfactory for general purposes. The white lights predominate in the ratio of two to one and are laid out in two groups _A_ and _B_. Both groups are controlled by the switch _C_. The switches _A_ and _B_ do not control the lights at all if the smaller throw-over switches at the right are thrown downward. A diagram of these switch connections is given in Figure 179 where the switches _B_ and _C_ are indicated. The object of the switches _A_ and _B_ is to help in quickly increasing or decreasing the illumination on the stage. If in the beginning of a certain scene, for instance, only a small quantity of light is wanted, while a little later full illumination is desired, the low illumination may be obtained by throwing the proper switches down; the additional illumination which will be needed a few minutes later may be prepared for by setting the other switches needed to the upward position and at the proper moment closing switch _B_; this will instantly produce the effect which otherwise would be possible only by operating a number of switches in succession. In the same way, by a reversal of this process, the illumination may be reduced in any amount. This feature is very valuable in many stage settings.

To throw off all of the white lights the switch _C_ must be opened. The switches _D_ and _F_ are main switches controlling colored lamps. All lamps of one color should be connected to one or the other of these groups unless some special color effect is desired.

From the three groups of switches, circuits extend into the foot lights, into every border, and into the proscenium side-light strips so that the color scheme may be carried out in any of these.

The handles of all switches in a row should be of the same height so that the operator may more readily accustom himself to catch them quickly. It is better to have switches of some excess capacity, as the heavy metal stands the arcing much better.

A main switch by which the whole board may be cut off should be installed but this need not be on the front of the board.

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Motion Picture Operation, Stage Electrics and IllusionsChapter XVIII: Theater Wiring (3)

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