Faulty RCD?

[pcsparky]

Can the RCD in the consumer unit be faulty. I have just had a new Volex CU fitted. One of the circuits on the RCD side kept tripping and I think I have found out that it was a loose wire in an outside socket.
However, now the RCD won't reset even with all of the circuits turned off. I'll try to get a new RCD tomorrow but was curious if anyone had come across a faulty one before.

 

[Spark123]

Does it reset with the main switch off?

 

[RF Lighting]

An RCD will not hold in if a N-E fault is present.

This fault will remain even if all the MCBs are switched off.

Do as spark123 said, and see if the RCD will hold in with the main switch turned off.

 

[pcsparky]

An RCD will not hold in if a N-E fault is present.

This fault will remain even if all the MCBs are switched off.

Yes it does reset when the main switch is off. But I can't understand why this morning the RCD worked fine with 2 out of the 3 circuits on the RCD side and now won't reset when all 3 circuits MCBs are switched off.

 

[RF Lighting]

Have you done any work on your electrics?

You say you found a loose wire at the outside socket, so I assume you have been removing socket fronts?

 

[pcsparky]

No other work. I found the loose wire because the outside socket is on the circuit that was tripping and I was checking to see if there was any moisture inside and found one of the neutrals loose.

Like I said before I sorted out this socket the other two circuits MCBs were working fine on the RCD. Having said that there were a few occasions when I tried to reset the RCD and it would trip as soon as I flicked it up. I had to turn off the MCBs, reset the RCD and then turn the two MCBs back on for them to work OK. That was another reason I was wondering if the RCD may be faulty.

 

[Spark123]

Whats the IR between N-E? Agree with RF, you may have distrubed sonething or caught a wire with a backbox screw? I have seen it before where someone put a surface mount plastic back box on with the cable entering through the knockout behind the screw lug and then used full length screws. It was screwed back and was getting a N-E dead short tripping the RCBO, when it was loosened off the fault cleared. It must have been like that for a while, the socket was in regular use for cleaners/photocopier etc. Well, the socket ended up being re-mounted a few inches higher with the cable entering through a different hole lol.

 

[pcsparky]

This gets even weirder. I'm not able to test at the minute but I was just checking an FCU where I know the screws are particularly long to check no wires were pinched and it's OK. Tried the RCD again and now it will reset on all circuits except one.
The weird thing is that it's a different circuit to the one I had problems with, that's working OK now.

So it trips on one circuit, then trips when all MCB's are off but will reset when main switch is off, and then trips on a different circuit.

Other than checking the FCU I haven't altered anything else. If it is a dodgy RCD why would it only trip on one circuit that was not tripping earlier?

 

[Spark123]

I doubt it is a dodgy RCD, it is more probable that there is a fault somewhere causing it to trip. Have you unplugged everything? Not someone swopping an appliance between circuits causing the fault?
Failing this, your best bet will be to get your test equipment out and test the circuits.

 

[pcsparky]

I know that it's not an appliance moving from one circuit to another. Yes, the RCD does seem to be doing its job but I can't understand why it is tripping inconsistantly. More digging will have to be done.