Following a local cut in supply, UK Power Networks installed a temporary generator (about half the size of a large container) at the local substation. There were 5 identical orange cables (about 25 - 35 mm in diameter) running from the generator to the substation.
Why 5? I had assumed 4 were the 3 phases and neutral, but if that was the case, what was the other one for?
GROUND.
Thanks. Why isn't the steel armour of the live/neutral cables used for the ground?
It can't handle the full fault current.
Singles can't have steel armour - unbalanced magnetic field inside. If they need a metalic sheath, it's a copper mesh, but those cables probably don't have any earthed sheath as they aren't expected to be used in location where that's needed. They'll just be double insulated single core flexes.
The generator (500kVA) was disconnected today. There were four 30mm diameter cables, but the fifth, which had been partially covered by the others, was in fact only 15mm. It was connected at one end by its ring to a clamp and 1200mm x 12mm earth rod.
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