Rcd tripping constantly - damp?

[London publisher]

Hi

I have a flat on two floors -- one in the basement. Over the last week the rcd has been tripping. It was intermittent at first and now the mcb in question won't come on without tripping the rcd. This coincides with some heavy rain.

It's a circuit with sockets on it, all of the basement level and half of the ground floor. All appliances are unplugged. There is a fused spur to some sockets outside. However I've turned off the switch. Still trips.

Any ideas? I suspect some kind of damp in basement. It got worse when it rained last night and went from intermittent to constant.

One of the Windows in the basement window well wasn't properly sealed and let it water which may have dripped into the wall. Could this be responsible? I've opened up the boxes in that wall and they look ok but one has a slightly rusty nail connecting the back box to the wall.

Or is it likely to be a wire in the wall somewhere?

Or could the outside spur be causing it, even with the fuse off?

Thanks.

 

[333rocky333]

Most fused spurs with switches are Double pole so turning switch off would isolate all your outside stuff.
Are the sockets and stuff inside chased in the wall, it is quite common for damp in walls to penetrate into a socket faceplate, its rare for damp to affect the cables unless they were seriously damaged when installed

 

[London publisher]

Thanks. Yep they're chased into the walls and with tanking in the basement. Hence I really don't want an electrician to start ripping open walls etc. Is there any obvious sign when damp has affected a faceplate in a way which will trip rcd?

 

[JohnW2]

Thanks. Yep they're chased into the walls and with tanking in the basement. Hence I really don't want an electrician to start ripping open walls etc.

As has been said, intact PVC cables won't let in any moisture/water, even if the cable is permanently submerged in water - so, unless the cable (both outer sheath and inner insulation) has somehow become seriously mechanically damaged, I don't think you have any need to fear any ripping up of walls. An electrician can test the cables without interfering with your walls.

Is there any obvious sign when damp has affected a faceplate in a way which will trip rcd?

I think that it generally takes a lot more than just 'damp' in an accessory to trip an RCD - whenever I've experienced RCD trips because of water ingress, some water has usually 'poured out' when I have removed the faceplate from the offending accessory.

Are you certain that everything connect to teh circuit has been disconnected? Appliances that can be unplugged are straightforward enough, but have any 'wired-in' ones been overlooked? Even they are usually supplied via switched 'fused connection units' ('fused spurs') - so, as Rocky has said, should normally be fully isolated if you switch that off.

Kind Regards, John

 

[333rocky333]

I quess the rcd is seperate from the mcb, was the Mcb going off as well as the Rcd, if so then the fault may be easier to locate

 

[London publisher]

the wired in things like the boiler and everything in the kitchen are on a different circuit which is still on. On the circuit in question all is unplugged.

I've looked in a few of the sockets on the suspect walls on basement level and there is a little corrosion/rust on the back boxes but the wiring all looks ok. Would this cause problems? No signs of actual water.

There is an electrician coming on Wednesday but trying to be as educated as possible before he comes.

Also had mice in the past but no sign of them for a while since I poisoned them six months ago.

 

[London publisher]

The mcb isn't going off though it has been known to in the past and did once in the last week. Now I can't turn mcb on without rcd tripping. And in the last few days just rcd tripping.

 

[333rocky333]

Ok that narrows it down to a L to E or N to E fault, which could be due to the damp, how near are the sockets to the suspect damp area.

 

[London publisher]

Well they're in a wall that's damp on the exterior. However, it has been tanked and got insulated plasterboard in front so no damp on internal decorations. However the back boxes are attached to the damp wall. They're supposed to be isolated from it but clearly aren't as they're showing signs of some rust. That said, does that actually cause an rcd trip? The wiring is only a few years old and the sheathes around the wires look ok.

 

[JohnW2]

the wired in things like the boiler and everything in the kitchen are on a different circuit which is still on. On the circuit in question all is unplugged.

Fair enough. When you say 'a different circuit', I presume you mean a different MCB. Do I take it that it's also a different rcd (if any) protecting that circuit?

I've looked in a few of the sockets on the suspect walls on basement level and there is a little corrosion/rust on the back boxes but the wiring all looks ok. Would this cause problems? No signs of actual water.

As I said, I would doubt it. The rust, per se, certainly won't, but even 'dampness' is unlikley to cause an RCD trip.

Also had mice in the past but no sign of them for a while since I poisoned them six months ago.

Certainly not impossible .....

Kind Regards, John

 

[Doggit]

As the problems crops up when it's wet, the most likely cause is the outside sockets, but Johns picture proves that everything's possible. As previously said, the rusty boxes aren't an issue, and the cables in the walls won't be, so unless there surface mounted cables that the mice could get to, it's unlikely to be that. If you're up to it, I'd take off the front of the outside sockets, and check they are dry, and see if there's any cable damage outside. The next thing would be to take off the fused spur, and disconnect the wires from the back, but that might be best for the electrician to do, but it is possible that the cable going through the wall have been damaged, and that might be the cause.

 

[333rocky333]

As discussed in the past a switched spur unit is almost always Double pole so would likely be pointless looking at the external sockets

 

[Doggit]

I liked the almost bit, I thought that was a nice touch. But your very likely right Rocky, just trying to help him eliminate things before the leccy turns up.

 

[JohnW2]

I liked the almost bit, I thought that was a nice touch. But your very likely right Rocky, just trying to help him eliminate things before the leccy turns up.

Strictly speaking, that's fair enough. However, I've personally almost given up including that 'almost'. A while ago I did a survey of all the SFCUs I had, in-service, used and 'taken out of service decades ago' (yes, I hoard ) - and I didn't find one that didn't have DP switching.

Has anyone here got, or seen, a SFCU with a SP switch?

Kind Regards, John

 

[333rocky333]

Im assuming more switched spurs are used for the Double pole isolation function just as much as the fuse down function, though don't run to TEN pages like the Boiler thread pleeze!!