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10
BRITISH KINEMATOGRAI'HY
Vol. 18, No. -2
Fig. 3.
Sixty A/.R Type 170 Arc Lamps assembled for Test at Shepperton Studio, embodying a Five-wire Circuit employing
the ■« Mole Float."
though their load was restricted to twenty Type 170's.
The plan finally settled on was to wire 132 Type 170 150-amp. H.I. arcs in seriesparallel, using the " Mole float," 26 G.E.C. 150-amp. H.I. twin arcs, 6 Type 1450 " Brutes," and all the " Duarcs " and the balance of the Type 170 H.I. arcs on the outers. In former demonstrations of series burning protection gear was dispensed with, but I insisted that every six arcs had a fuse protection. At this stage this did not corrplicate the problem, as each 600-amp. circuit was switched and fused and the whole of the series equipment was connected to the silent stage permanent wiring.
The speaker described in amusing fashion the problems of wiring this quantity of equipment. He continued :
The next difficulty was that the photographer was in the habit of setting his key
light first, and then lighting his sets. Under this system, and until a balance is obtained (which is only a matter of seconds but has to be done continuously) the amount of light is bound to van' as the voltage across the arcs goes up or down.5
Balancing the Loads
With experience this variation was almost eliminated by the controlling electrician lighting or " killing " an arc to bring the whole circuit into balance. From observation, it seemed he chose a position on the rigging (after seeing the extent of the camera angle) and used two to six arcs not in use on that particular shot for starting an I balancing purposes, balancing entirely by eye and the colour of the arcs, having in front of him a drawing so that he could see at a glance which lamps were on which side.
The conclusion from the photographer and the " gaffer " at the end of two days'