Cable replacement trips RCD

9 Jan 2019
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United Kingdom
Hi all,

I have recently replaced one of the sockets in my house and for some reason it is tripping the RCD on the consumer unit. Can anyone help please?

A little background info,
Following some recent works on the house I have had to replace an electrical cable to a socket as the original cable wasn't quite long enough to reach the socket in the new position. Since I have done this, the RCD keeps tripping. I have replaced the cable with the same size and spec.

I have tried several things to see what is affecting this.
- I have replaced the socket with a different one to see whether this is at fault (but still trips)
- put the original cable back in to check if its the new cable (but that trips)
- bypassing the socket altogether (but still trips)

The only way the RCD wont trip is if the earths are disconnected from the consumer unit. Even if the circuit breaker is off for this circuit and the earth is then connected then the RCD will trip.

The socket is on a ring circuit (dedicated solely to sockets), using a twin 2.5mm and earth cable. The circuit breaker for the sockets is B16 but this doesn't trip. The only other connection on this RCD is the kitchen ring circuit that is connected to a B32 circuit breaker.

Can anyone help please? Before the cable was replaced the circuit worked but since replacing this cable it seems to trip.
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If the MCB for the kitchen sockets is off ,and the MCB for the other circuit is on does the RCD trip ?
And re connect the earths that you have disconnected ,if you have not already done so.
Interesting you've got a ring final protected by a 16A MCB- makes me think this might be a radial instead.
First thing, you MUST isolate the consumer unit before working inside it- ideally there'd be an isolator between the meter and the CU. Just using the big OFF switch in the CU doesn't isolate it- you still have live phase inside the CU.
Second, reconnect the earths in the CU right now (in the terminals that they were originally in- this makes subsequent testing and fault finding much easier)
So now you have a safe installation with (presumably) an RCD that won't hold in. You now need to determine where the fault is.
Most likely you have a neutral-earth fault, again probably (but not definitely) on the cable you've installed. Check both ends of this cable for nicks in the insulation- it is very easy to nip cores when screwing sockets onto backboxes. Check any other cables at the point you've terminated the new cable at for similar faults. If you had a multimeter you could try testing for N-E faults at the CU (might get a hit, might not)- low odds you've got a Megger so no point suggesting it.

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