Lower ring tripping RCD - troubleshooting tips please

[elrao]

Hi

Moved into our house a year ago and electrics were fine for 4-5 months and then the RCD tripped. By a process of elimination I concluded it was the lower ring that only supplies are dining room and one external socket that was tripping the RCD, so by leaving the 'circuit breaker' for that ring 'Off' I could turn the RCD back on and the electrics in the rest of the house work fine.

I removed all devices from all sockets on the ring and turned it back on and within 45 minutes it tripped again, so it has been left off for the past few months as the problem must be in the ring wiring somewhere.

Time has finally come to try to work out why it is tripping and see if it is a DIY fix or I need a sparky.

The ring is switched off and we have removed all the socket covers and cleared out all the dust that was in there. We have done some basic continuity checks and there is continuity between the earth and the Neutral which doesn't sound right to me...but wanted to check with someone who would know for sure before we try to hunt down where the short is (if there is one), I can't think of any work that has gone on (suuch as nails into walls etc.) that might have caused it though?

Thanks in advance

Rob

 

[RF Lighting]

It is normal to see continuity between neutral and earth on a circuit which is still connected to the CU, and the main switch is on.

If you try the test with the main switch off, the continuity should not be there.

It is more likely though that you have a fault between live and earth as isolating the MCB has stopped the RCD tripping.

If you had a N>E fault, it would still be present with the MCB off, and the RCD would have continued to trip.

Unfortunately, you are unlikely to be able to trace the fauly with a standard multi meter.

Yuo are doing well to check all the sockets for any signs of damage to the wiring behing them. Also look for any signs of damp / rusting / corrosion to the backs of the sockets.

Also, pay special attention to the outside socket for any signs of water ingress, and any damage this may have caused. The fault can still remain even if the socket has dried out (such as carbon tracking)

 

[dannyboi2003]

I agree with RF, my first thought would be the outside socket. If its a spur from the ring find where its spurred from if you can and disconnect it. Restore power the the circuit and see if thats solved the problem. If not then as RF said it gets a little more difficult.

Let us know how you get on

 

[elrao]

Thanks guys. We had come to the same conclusion about the E>N as all the Neutral wires are connected in the CU, so if it was a problem on that ring then it would be a problem on the others still!

Looks like we have two external connections, one is a direct socket and the other is a connection box which leads to an armoured cable ... which leads under the ground and we have no idea where it goes!

Will try disconnecting the spur for the external plug.

 

[rebuke]

Do you have a shed/garage/greenhouse at all that has power in it, or any outside lighting as that would be the traditional use of an armoured cable in this sort of scenario. If not, then upload some photos of the connection box and the armoured cable, it might potentially give people on here a clue as to its purpose...

 

[elrao]

Yes there is some outside lighting, some of which works and some that doesn't! Trying to work out where all the cables go is a nightmare! Have disconnected both the armoured cable and the external plug spurs. Circuit is now on and has been for about 5 mins without tripping...fingers crossed.

Just got to work out where that cable goes now!

 

[rebuke]

Ah, then the most likely scenario is water ingress to either the outside socket, or one of the lights (which could be caused by a variety of things - seals breaking down, not using weatherproof SWA terminations outside etc)