MCB trips rcd

GreySquirrel

MCB trips rcd.

I have a 25 A RCD type A and a 20 a MCB and cable to one double socket.

the RCD can be set and will trip with the test button. However when I set the RCD and then set the MCB, the RCD trips.

Any ideas I should be looking for? I haven't ckecked the double socket yet. No light in that room at moment

meercat

possible neutral - earth pinched behind socket
or retaining screw through neutral wire

sparcocars

GreySquirrel wrote: »

MCB trips rcd.

I have a 25 A RCD type A and a 20 a MCB and cable to one double socket.

the RCD can be set and will trip with the test button. However when I set the RCD and then set the MCB, the RCD trips.

Any ideas I should be looking for? I haven't ckecked the double socket yet. No light in that room at moment

Yeah it definatly sounds like a neutral to earth fault on the circuit supplied by the mcb. More than likely at the socket as meercat said.

GreySquirrel

I had the cable neutral connect to the neutral bar instead of returning via the RCD. Will fix tomorrow and report back

Bruthal

sparcocars wrote: »

Yeah it definatly sounds like a neutral to earth fault on the circuit supplied by the mcb. More than likely at the socket as meercat said.

Probably worth a mention that a neutral-earth fault tripping the RCD as in the OP, doesnt certainly have to be on the MCB circuit being switched on when the problem is occuring.

There would have to be a load on the circuit the MCB is controlling for it to happen though. Just as there would have been, to trip in the case here with wrong neutral bar connection.

GreySquirrel

Ok, I've connected the neutral to the the RCD. The MCB no longer trips. I have only one double socket on that circuit and testing with a lamp shows it working

M cebee

you're testing the circuit with a lamp?

GreySquirrel

M cebee wrote: »

you're testing the circuit with a lamp?

just for the moment. tools elsewhere