Temporary power generation

[Jeff Layman]

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?

 

[Jeff Layman]

GROUND.

Thanks. Why isn't the steel armour of the live/neutral cables used for
the ground?

 

[Andrew Gabriel]

Thanks. Why isn't the steel armour of the live/neutral cables used for
the ground?

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.

 

[Jeff Layman]

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.