Voltage on fittings in bathroom

[Dartlec]

I think you're missing that the first picture shows two off T&E going up through the hole, then the next picture shows one cable in the socket back box. I agree, the two white lines below and to the right of the socket do look like paint runs.

I can't help thinking there's a joint in that wall, and it's "not been made very well". Or even, that there's a nail through a cable providing a path through the insulation to make the timber live. In terms of conductivity, it's dissolved salts that make water conductive - and there'll be all sorts naturally in the timber, plus plenty of plaster dust etc from construction. As pointed out, it won't be a very low resistance, but it doesn't need to be to give a tingle.

Westward is right - in the picture I'd already pulled the two grey (Imperial) T&E cables down into the ceiling below, so there were no cables left in this wall - or at least none that were visible or could possibly be running anywhere....

The little cable left in the back box is the original earth strapper with green sleeving. The white flexes to the front are an extension lead that was plugged in, and the aerial lead to a TV on top of the chest of drawers. There's absolutely nothing powered in the bathroom other than the ceiling light, with external switch....

There was nothing to suggest there should be another joint in this wall, at least on the socket circuit involved - plumber checked in the loft to ensure there were no leaks from above. There is a switch wire to the bedroom light, but the stray voltages only occurred with the socket circuit on.

It is possible that there was a junction box somewhere else under the floor, but with a ply floor no easy way to confirm it and beyond the reach of the access camera the plumber had handy....

So everything at the time pointed to it being this socket - but looking at it on paper I'd not think it was either!

It was an original MK single socket (vertical screws), so its possible that it had failed in some way that energised the back box, but the box was not damp to the touch and there was no sign of moisture behind the socket. The wall seemed mostly dry at that point, though there could well be the dissolved salts/plaster that could still conduct some...

The socket appeared in good condition too for its age...

If I do go back to change the CU I'll certainly be giving this circuit a much more thorough investigation - and wouldn't reinstate that socket without a lot more work involved on the wall.

Her insurance company will likely be involved so we'll see what comes from it....

 

[Dartlec]

something wrong there. 2 x T/E going up into the wall, but not to that socket back box, which has 1 cable running through it, .

The cables had already been pulled out by that time - the only wire in the box is the remaining earth strapper with green sleeving...

 

[captaincaveman]

I got failed insulation readings between conductors and wall once. found the culprit to be a nail through the skirting board. Amazing how conductive building materials can be!
I would check the cable to make sure it's legit as I've come across fake cable before where the insulation doesn't stop water (Sorry, Lucien Nunes - I still have your sample here on my bookcase. I'll get round to sending it to you one day lol)

 

[Petej999]

If there was no water or damp in the socket then I suspect there's possibly still a damaged cable, cable with a screw or nail in or junction box somewhere any or all of which have water around them.

There's a path from Live via water to tap / radiator somewhere.

OP wouldn't trust a pen / volt stick if I were you a very misleading tester imo,

 

[brianmoooore]

OP wouldn't trust a pen / volt stick if I were you a very misleading tester imo,

No sane person 'trusts' a Voltstick for anything, other than if it lights up when a circuit should be dead, it means that something is not as expected, and you should proceed with extreme caution.
For this reason alone, they are invaluable.