RCD trips when one MCB is switched off.

[Malakym]

I've got a nuisance trip issue at the moment that I'm trying to track down.

One thing I've noticed is that if I switch off one of the MCBs (on the RCD) side the RCD trips and will not turn back on until the MCB is turned on. This is one specific MCB and none of the others do this.

Any ideas? I'm assuming this is related to my issue.

 

[chivers67]

In the first instance I'd check the circuit neutrals are in the correct place

 

[Adam_151]

One thing I've noticed is that if I switch off one of the MCBs (on the RCD) side the RCD trips and will not turn back on until the MCB is turned on. This is one specific MCB and none of the others do this.

Will the RCD set with all the MCBs it feeds switched off?
What about if all the cirucits are turned off (even ones not supplied by it)?

With the MCB in question and the RCD both on. Does the test button on the RCD work?

 

[Murdochcat]

Have any changes been made to the installation ?

Drilled any holes ?

 

[Malakym]

Would that suggest a nutural from the RCD side or not RCD has been switched?

I have moved the CU up the wall slightly so rewired it to match, though removed one MCB from the RCD side (a single light was in this) and moved the wires to another MCB on the non RCD side. Since this was the only (intended!) change I have removed these wires (and left them disconnected) with no luck.


I am trying to figure out what to unplug on the MCB that causes the RCD to trip intermittently in the late evening (we have no timers, PIRs or frost cycle fridges that could run at a late time).

The MCB in question is labeled sockets but we have a few such MCBs and the sockets are in a bungalow there isn't really a sane layout (some rooms have sockets on different MCBs in them, and I've yet to map it out fully).

 

[ericmark]

I had a new consumer unit fitted, and there were some issues with borrowed neutrals, which in my case was on the lights. I test with a clamp on here showing a total of 8 mA leakage for whole of house, the problem is there is always some leakage due to capacitive and induction linking, and in a no-fault situation this should be no more than 30% of the RCD rating, so with a 30 mA RCD allowed a maximum of 9 mA. For years, my meter increments were 10 mA, so it was a little hit-and-miss, however the RCD tester will test it does not trip at 15 mA and does trip at 30 mA and in the main they will actually trip at 26 mA, so if it passes, 26 –15 = 11 mA so should not be that far out.

Clearly you will have inspected and tested when you did the move, so what were your results?