UK Odd Electrical Fault in bathroom between taps and tiled wall

Broadway21 · Apr 7, 2024

Hi there, I’m a new member to the forum and felt like I could do with some additional insight into a fault I came across on a call-out at the weekend.

I was called to attend a domestic property where the tenant had mentioned getting a shock when touching a tiled wall and the bath taps.

On arrival and inspection I was in fact getting varied readings around 24v when using my voltage indicators between the two.

When isolating the first floor socket circuit the fault appears to clear and I can no longer measure voltage. On further inspection there is a spurred single socket on the other side of the wall, this is fed from a blanked point which I assume was part of the ring final, also on the same all but approx 4ft away inside a cupboard. Disconnecting the spurred leg to the single socket and energising the circuit again also seems to clear the fault.

The tiling has clearly suffered damage in areas with some tiles being replaced really badly, so my initial thoughts were somehow that spurred leg has got damaged and water ingress has soaked that wall causing the issue. Voltage is measured specifically around the areas of damaged tiles and not higher up the wall.

My concerns lie with the the fact that this circuit is protected by a 32a Type A RCBO, which has not tripped. This is a TT earthing arrangement and I have measured 47.5ohms, visually the clamp looked ok. Bonding was seen to gas and water services in the garage correctly located but I hadn’t verified via a wander lead.

The RCBO appears to test out fine on 1x/5x tests and also ramp tests.

Prior to disconnecting the spurred point I measured really low IR readings across L to E and N to E. Again when disconnecting the spurred leg, the IR improves to 120Mohms plus.

For good measure I tested the spurred leg that is on the wall the other side of the bath when completely disconnected and I get 999Mohms. So this confused me even more if I’m honest.

Some outside opinion would be great to see if I am missing something blatantly obvious here. Could there be some plastic paperwork preventing adequate bonding of pipe work to taps? Why has the RCBO not taken out the supply to this circuit etc.

Thanks in advance and apologise for the long essay.

Regards

UNG · Apr 7, 2024

What voltage indicators were you using I'm wondering if you were seeing some level of ghost voltage

snowhead · Apr 8, 2024

The RCD isn't tripping as the fault current is (way) below the tripping threshold.

I can assure you from personal experience, as will some others on here, that discomfort level can be quite high and an RCD, that tests perfect within limits, will not trip.

The cable in the tiled wall will be cut, or have a screw or nail in it.

brianmoooore · Apr 8, 2024

Similar to the one I had, where a non contact voltage indicator (Voltstick) would light when I put it near the earthed metalwork of a nearby socket. Took a little while too realise that the earthing was fine, and that it was me, along with the walls and floor that were live.
Turned out to be a cable with a screw through the live on a nerby wall.

Rockingit · Apr 8, 2024

I'm assuming that these have to be stone or another non ceramic tile?! I'm also assuming that you've verified water bonding and maybe gas as well if that's the source of DHW. You might also want to check all other exposed conductive items elsewhere to be sure it's not actually a back-fed earth fault coming in.

But as others have said - the electricity hasn't just decided to up-sticks for a better view and decided to live in the wall, it's been put there by accident so you're looking for some penetration damage from either side or worse, a route through you, Don't also discount that it could have been a slice into a cable via a tilers trowel if there's any cables that may live just under the tiles (such as if someone's put a lazy shallow chase in to feed a light or shaver point).

And - the challenge here won't be finding what's gone wrong, the challenge will be putting it right again without destroying Mrs Jones' bathroom, so good luck!

Broadway21 · Apr 9, 2024

Thanks for all your replies, it is greatly appreciated.

As per some of your questions, I was using the megger TFT voltage indicators and they did appear to be basic ceramic tiles.

I have not confirmed water bond via a wander lead to pipe work beneath the bath as I didn’t get round to looking at removing bath panels etc. But I could visually inspect gas and water bond runs to the clamps on each of the services as both the meter and the stopcock were located in the garage, with the clamps also correctly located and tight. I should have maybe verified this which I may well do when I return in the future.

As you have all mentioned it is most likely a damaged section of cable sitting in a damp wall, that could have been affected but the tenant damaging the tiles and attempting to replace them. It was just that the cabling feeding the socket on the other side does appear to run in zone but all I have to go off are how the cable enters each back box via side knockouts. Which isn’t exactly where the damage in the bathroom has occurred.

The other thing that confused me was that when IR’ing that one section of cable, I got an excellent reading to suggest the conductors are in tact, but I suppose that doesn’t rule out a slice in the outer sheath exposing copper on the Line conductor which is getting wet within the wall.

Just to throw it out there, I also managed to measure voltage between the line conductors in the old blanked off point in the cupboard, to the metal clad back box, but it is not conduit earthing system, no signs of nicks in the sheathing as if enters enclosures and it is plastic conduit bringing cabling into the back box. So just bloody random to me and I felt like I was missing something here, hence the post.

Thank you all again I really appreciate your thoughts it always helps to get another opinion.

Many thanks

DefyG · Apr 9, 2024

There could also be a completely unsuitable junction box embedded within the wall and tiled over or just cables in choc blocks in old accessory box such as these found on a job that had been plastered over!
Lost count of times have come across something like this!