On 20-Jan-17 6:33 PM, Caecilius wrote:
I suspect this isn't possible, but I thought I'd ask just in case...

I've got a large office with a 3-phase electrical supply. But I don't
have any 3-phase equipment; I split the 3 phases to 3 x single phase
sub-mains feeding CUs on each floor.

The original building has a 3x60A supply, but that was upgraded to a
3x100A supply about five years ago. I don't think our total draw ever
exceeds 100A, so in theory we could operate from just one of the
phases.

We have regular power outages, all of which are acknowledged by UK
power networks and normally involve some sort of problem at a
substation. But strangely they don't always affect all three phases.
Hence my question:

Is there a way to convert a three-phase supply to some sort of
redundant single-phase supply? I wouldn't want something that
involves power-loss, as the 3-phase supply comes into the basement and
I don't have any easy way of getting rid of heat from there; but even
some sort of "throw the switch Igor" switchover solution would be
better than I've got at the moment when I end up losing a random floor
(and typically the CH boiler as well, which means we need to close the
office when it gets too cold).


How about three double throw contactors, each powered by one phase and
wired so that it passes that phase through to its associated CU when
powered, but switches to another phase when the power fails? It should
work completely automatically, with minimum down time, and they
shouldn't draw enough power to cause you heat gain problems.

If you want to allow for the possibility of two out of three phases
failing, a second contactor in series after the first and powered by the
output from the first would allow you to switch in the phase that isn't
connected to either pole of the first if both of those fail.

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Colin Bignell