In uk.transport.london message , Wed, 14
Apr 2010 10:28:42, tony sayer posted:

And that much difference in overall power supplied 650 V single phase
rather then I presume 415 or 440 or was it actually 400 three phase?.

Take your point re more cable required seem the price of copper is on
the up again.

For the same power, three-phase requires little over half of the amount
of conductor in comparison with single-phase. Consider three single-
phase supplies driven at 120 degrees to each other : obviously the live
wires deliver the same AC current as the live wires in a three-phase
supply, but three neutral wires are required. Now join the three
neutrals into one; the three return currents, being of different phases,
add to nothing, with balanced loads; therefore the neutral, carrying
only off-balance currents, can be comparatively thin. See sig.

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