electrical....

well I guess..there is such a thing as a three phase RCD.

Fit it to the bench.

I found several on offer - around 50 quid for a 30mA one.

Tim,

I have several modernish three phase distribution boxes here on the farm all by Wylex. I simply removed the main breaker and replaced it with a compatible three phase RCD one. Conventionally workshop machine are on 100mA rcd trips but I feel happier with all mine at 30mA, particularly as several machines have a standard 13a double socket on them powered from phase 1. To date not had any nuisance trips. Single phase distribution is from a separate box, also with a 30mA trip.

If your distribution boards will not accept an RCD main switch for some reason, just intercept the three phase feed, and bring it via a three gang box with an rcd mounted in it.

AWEM

In message , Andrew Mawson writes

Umm... I assumed there would be a problem with starter coils being across only two phases or even phase neutral. Local inspection lighting phase neutral.

The other unknown is DC injection braking on circular saws.

regards

Yes. See reply to Andrew.

regards

That is the correct answer (or would be if I was doing the work).

Thinking about it logically provided all the current that is going into the lines is also all coming back on "safe" lines, all is well. It's when you don't get it all back that you assume it's going to ground, possibly via someone, so you trip the power.

This implies that you monitor the three phases and the associated neutral. How you actually do that I haven't a clue and in delta connected kit there isn't a neutral to monitor, I think. I know enough about three phase to know I'm dangerous...

It should not matter... the sense coil is round all phases and neutral. As long as the vector sum adds up to zero, then it can assume all is well. Only when some current returns via a path that does not include the RCD does it trip.

OK chaps.

That is clear enough.

Borrowed neutrals would be a mistake but otherwise get on and do it:-)

thanks.

regards