3 Phase Inverter trips RCD but only when switched off

[zebedee2001]

Howdy Folks...

Slightly oddball fault. I've had a 3 phase inverter for some time but never got round to fitting it, lent it to a friend as his went wrong, he used it & all was fine. He gave it back to me the other week & I decided to fitted it this week to my garage.

I have wired it in to its own MCB in the consumer unit in my garage. I have fitted a double pole switch in line with it (to aid isolation). The inverter switches on fine & runs OK, however if I switch off the inverter by the double pole switch it trips the RCD in the consumer unit. I can reset the RCD & all is fine. If I switch it off via the MCB it doesn't trip the RCD. The inverter runs on for a while with no load when the power is isolated.

I don't get how double pole isolation causes the RCD to trip but single pole isolation doesn't.

Thoughts please!

 

[JohnW2]

I don't get how double pole isolation causes the RCD to trip but single pole isolation doesn't. Thoughts please!

Definitely odd, but I seem to recall that we heard here of something similar in the fairly distant past.

It's not, in itself, an obvious explanation of how/why it could result in an RCD tripping, but one thing DP switching can possibly do that SP cannot do is to break the neutral before breaking the l line - which is perhaps something to ponder.

Kind Regards, John

 

[securespark]

Definitely odd, but I seem to recall that we heard here of something similar in the fairly distant past.

I posted the following in 2004...

I had a neutral/earth problem today. I reinstated power after fitting a S/L board, and one of the rings tripped. I switched off the affected circuit, but the RCD refused to reset until ALL the circuits on that side had been isolated.

Then the RCD remained on until the same ring was switched on again.

The odd thing was that the RCD tripped when I switched off the main isolator for the CU.

I found a faulty fridge, unplugged it and all was fine.

The cause? N/E reversal in the plug top............