RCD Tripping – Fault Traced to One Socket, Still Trips with Replacement

[icon_boy]

I'm having an issue with an RCD that keeps tripping as soon as I attempt to turn it back on. I've already unplugged all appliances from the affected circuit, but the RCD still trips immediately. To isolate the fault, I disconnected each socket on the circuit one by one and managed to trace the problem to a single socket.

When this socket is disconnected, the RCD resets without any issue. However, when I install a brand new socket in its place and wire it up, the RCD trips again as soon as I attempt to turn it on.

This suggests the issue might not be the socket itself but potentially a fault in the cable feeding it. There are no obvious signs of damage, but I haven’t carried out any insulation resistance testing yet.

Looking for advice or confirmation from anyone who's seen a similar issue — is it likely to be a neutral-to-earth fault or some other wiring issue in the cable?

 

[Harry Bloomfield]

When this socket is disconnected, the RCD resets without any issue. However, when I install a brand new socket in its place and wire it up, the RCD trips again as soon as I attempt to turn it on.

Is this circuit a ring circuit, or a radial? Assuming you believe it forms an integral part of the ring, rather than a spur, have you double checked it is definitely and integral part of the ring?

If it has two cables behind it, then possibly, it might be a spur, looped to another socket, which is the one at fault.

 

[icon_boy]

I believe it may be a radial circuit protected by a 32-amp RCD. I say this because the electrics were rewired in 2015, which is when the extension was built. The extension appears to be using the same circuit as well.

 

[Jurassicspark]

I believe it may be a radial circuit protected by a 32-amp RCD.

I think you mean the 32A MCB.

Before digging in more, could you send a picture of the fuseboard and what exactly is tripping and what is supplied from the MCB.

What size cable is feeding the socket? If it's really a 32A radial then it should be at least 4mm. If it's 2.5 then it suggests it's ring but it needs testing beforehand.

I say this because the electrics were rewired in 2015, which is when the extension was built. The extension appears to be using the same circuit as well.

It sounds like when you take off the socket, one of the faulty legs of the radial circuit gets disconnected and the rcd doesn't trip.

A insulation resistance tester is needed to test both sides of the radial. Any work was recently carried out?

If you know how the circuit is wired up, you can run a temporary piece of twin of earth and bypass one socket, one at a time with the original cable disconnected, this should rule out where the fault is.

 

[icon_boy]

Please find attached an image of the fuse box for reference. The cables connected to the socket are 2.5mm in size. I have not had any electrical work carried out recently; the only activity was some painting and decorating, which took place approximately a year and a half ago.

The circuit initially tripped late last night, just before I went to bed. I disconnected all appliances from the sockets and was able to reset the RCD. However, the circuit tripped again this morning. Although all appliances had remained unplugged since last night, my partner had plugged a phone charger into the affected socket.

After removing the charger, I attempted to reset the RCD again, but this time it would not reset. This is when I began removing the sockets to investigate further.

 

[EFLImpudence]

That is an MCB (Miniature Circuit Breaker) that is switched off; not an RCD (Residual Current Device).

If that is what has been tripping then you must have a short-circuit fault (L to N) or an Earth fault (L to E - any E, not necessarily the Earth wire).
This is likely to have left a scorch mark at the location of the fault and as it won't reset likely to be still touching.

 

[Scally-Ho]

Mice? Are there any signs of rodents in or around your property, because rodents are a common cause of wiring faults.

 

[icon_boy]

Mice? Are there any signs of rodents in or around your property, because rodents are a common cause of wiring faults.

no signs of any rodents, at all..time to get an electrician out - thanks all.

 

[Jurassicspark]

no signs of any rodents, at all..time to get an electrician out - thanks all.

A 150W light bulb connected to each of the conductors from L to N or E should tell you where the short circuit is.

 

[ericmark]

A 150W light bulb

I remember them, use to have them years ago.

 

[endecotp]

Hung any pictures on the walls recently?

 

[Harry Bloomfield]

After removing the charger, I attempted to reset the RCD again, but this time it would not reset. This is when I began removing the sockets to investigate further.

The tripped item, in your photo, is a 32amp MCB. Is that what is tripping or the RCD to it's right, with the yellow button with a T marked upon it?

I believe it may be a radial circuit protected by a 32-amp RCD. I say this because the electrics were rewired in 2015, which is when the extension was built. The extension appears to be using the same circuit as well.

A radial on a 32amp MCB, would need to be wired in 4mm, not 2.5mm. 2x 2.5mm appearing at the MCB terminal, would suggest a ring, but you would need to test that to confirm it is actually a ring.

The best way forward, is to isolate sections of the circuit, and test each section for faults. The actual fault, could be due to almost anything - a wire adrift behind one of the sockets, a screw or nail which has worked it's way over time, into a cable, or rodents chewing the cable.

What ever you decide to do, make sure the power is isolated, before touching anything, and don't go prodding around inside the consumer, unless you have an external means to isolate the entire supply to that first.

 

[icon_boy]

The tripped item, in your photo, is a 32amp MCB. Is that what is tripping or the RCD to it's right, with the yellow button with a T marked upon it?

I have isolated the MCB as it was causing the RCD to trip.

its best I get a electrician in

 

[Murdochcat]

I have isolated the MCB as it was causing the RCD to trip.

its best I get a electrician in

Maybe come back when it’s fixed and update us

 

[crystal ball]

Any outdoor sockets, lights or other equipment, first place I look, also a couple of instances of similar faults were caused by water ingress in junction boxes from drips from leaking pipes