On Friday, 20 January 2017 18:33:13 UTC, 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).

All you need is three contactors and a single pole, three way (rotary?) switch.
http://www.ebay.co.uk/bhp/rotary-switch
It would be ideal if they were also mechanically interlocked.