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Along both side walls of studio a series of plugging boxes is arranged. Each box consists of a 3-wire 100 ampere (per side) plugging pocket, fed by rigidly installed wires from the switchboard. The boxes should not be more than fifteen to twenty feet apart and about four feet above floor. The pocket openings should be downward. This will prevent their being used for ash trays or storage receptacles.
To each of these pockets is fitted a 3-wire plug attached to a 3-wire stage cable of equal capacity, 20 to 30 feet in length. Each of these cables terminates in a portable spider or plugging box having four 2wire pockets each of 50 ampere capacity.
The plugs fitting these pockets are attached to the lamps by stage cables of suitable length, usually about 25 ft. In this way each wall pocket would supply four lamps of 50 amperes or less, with a large radius of movement for the lamps.
The switchboard is fitted in addition to the top light switches, with one switch for each plugging pocket, each switch being triple-pole, double throw, with the blades connecting to the plugging pocket. One throw of each switch is connected to a set of bus bars fed through a master switch, the other throw of each switch is connected to a separate set of bus bars, fed either through another master switch or direct from the service.
This enables the electrician to set his switches and lamps so that upon signal he can turn on or off a portion of the lights in a set without disturbing the rest; so that a light change can be played in a scene. In the old days this was usually done by holding the action, stopping the camera until the light change was made and then resuming action.
Before concluding, I want to dwell upon the use of alternating current in the studio.
In the third report of the Society proceedings, a reference is made (Paragraph 6 Report of the Committee on Electrical Devices) to the use of alternating current in the projection arc. The objections cited apply here with only this difference, that in projection there seems no real remedy except converting or rectifying to direct current, while in the studio the remedy is simple on account of the plurality of the light sources. All that is needed, to overcome the phase flicker, is a two phase installation with the lamps properly distributed and balanced on the phases.
A word of caution here to the camera man may save him many feet of retakes.
The exposure variations resulting from phase flicker become particularly pronounced on close up, dissolves and fades. This is due to the variations in the exposure period as the shutter opening in the camera is varied, and as close ups are often made with a single lamp, a flicker results, much more pronounced than that in alternating current projection, where at least the shutter value is constant.
To obviate this, never use a single lamp on alternating current, but always arrange the lamps in pairs connected on opposite phases; the results will surely justify your taking the trouble to see that this suggestion is carried out.
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