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BRITISH KINEMATOGRAPHY
Vol. 18, JNO. 2
ECONOMICS OF THE FIVE-WIRE CIRCUIT
C. G. Heys Hallett, M.A., A.I.P.E. (Member)*
THE previous paper establishes beyond doubt that series running is now a practical proposition on any size of set, and much value can be obtained from a study of the difficulties encountered.
The set in question represented the most complicated cabling which can be encountered. The studio has a 3-wire system, and it was required to mix large numbers of lights in series-parallel with others running in parallel, many being fed from 600 amp.
sisted of generators connected in series supplying 600 amp. gantry panels. Now suppose that half the generators were removed, the remainder connected across the outers and the neutral disconnected. If the set is now cabled up, using all the standard 3-wire cables and boxes, the only variation from normal practice which will be required is as follows: All lights requiring 115 volts, such as incandescents and " Duarcs," are connected across the outer bars of the con
Fig. 5. Five-wire Connecting Box for use with " Mole Float.
gantry panels. The " Mole float " must, of course, be continuous throughout the set, and considerable thought was, therefore, necessary while connecting it up between circuits. On a twowire system it is necessary to watch the balance of the " Mole float " in relation to the positive and negative, but on a 3-wire system, it is not only necessary to watch the balance of two " Mole floats," but also to watch the out-ofbalance current in the neutral, so the 3-wire system is at least three times as complicated. How simple large scale series running could be is indicated by the following analogy: Suppose that a 3-wire system con
necting boxes, while arcs to be run in series are connected, without grids, between an outer and the centre bar; what was the studio neutral bus-bar is now providing most of the " Mole float," and the remainder will consist of what would otherwise be regarded as normal 3-wire cable runs.
Adaptation of 3-wire System
For studios which already have a 3-wire system, it is possible that cabling would be much simplified by the use of a 5-wire connecting box (Fig 5). This type is fitted with work lights which also operate as polarity indicators.
Mole-Richardson (England) Ltd.