Socket develops fault, trips RCD

[very_pointy_ears]

Hi,

Last night I was minding my own business when suddenly the RCD trips out.

I work out that the circuit with the fault is one of the ring mains (the only ring I haven't actually worked on aside from actually wiring the ends into my new CU). I go round pulling out all plugs from the sockets on that circuits and the RCD *still* won't stay up (I switched all other MCBs off so I'm just testing that one circuit).

I eventually discover that, despite nothing being plugged in to it, I have to turn the switches on a particular socket into the off position before the RCD will stay on. Leaving nothing plugged in, if I flick the switches into the on position the RCD trips out immediately.

I replace the double socket with a new MK one I happened to have and it's all fine now.

Does this sort of thing happen often? The old socket is about 20 years old (I assume - it's in the extension which was built in 1987 and I assume it's original). There's no visible mechanical damage nor is there any indication of it getting wet (it's on an internal wall anyway). It's not a make I've heard of before but then again I'm not an electrician so I don't see many installations to that level of detail.

My wife wasn't best pleased because it happened in the middle of her recording a film on Sky+ ...

 

[THRIPSTER]

Could be that you have disturbed a fault in the cable behind the socket or there is a depressed spider between line and neutral in the old socket

 

[very_pointy_ears]

I don't think I've disturbed anything - not only have I not worked on this cicuit, I've not actually worked on this entire wall, from either side.

The spider theory is an interesting one - I'll have to open it up to see.

 

[RF Lighting]

Sorry to be a pessermist, but I bet it's tripped again within the week.

 

[very_pointy_ears]

I hope not! Though I bow to your far greater experience. Why do you expect it to re-trip within a week? Because there are other old sockets the same as the one I've just replaced or for other reasons?