"andrew" wrote in message
...
One of the legacy sites I still do a bit of maintenance on has a
large
sealed thermal store with plate heat exchangers for DHW plus an
underfloor
loop. It is normally solar powered with a wood burner for high
demand.

It has a 3ph delta wired immersion heater provided as back up but,
due to
cock ups in communication there is only a single phase supply.

Obvious solution is to pull the 3ph immersion out and replace with
240V one
but nothing has been done about this in 4 years. Spare parts for the
wood
boiler take about 3 days to source and fit so there is a need for a
back
up.

I talked with the electrician and pointed out one could supply 240V
across
two of the immersion terminals and neutral on the third, which would
drive
~0.6 of the current and produce 1/3 of the heat of each element in
the
immersion. So the 9kW 3phase immersion would derate to 2 elements at
1kW
each, still better than nothing if the 240V supply is up to it. The
suggestion was immediately condemned as unsafe and inappropriate.

I can see that it would be in defensible as it is using equipment in
a way
for which it isn't designed but unsafe? After all it's using 0.6 the
voltage and current it was designed for.

AJH

If the six wires that are the two ends of each of the three heating
elements are accessable, then they just need wiring so that the
elements are in parallel to run off single phase 240v. I did precisely
this with a large three phase pottery kiln which was entirely
satisfactory (except for the eletricity bill!)

AWEM