Possible Cable Fault?

[jus001]

Hello,

I have had a problem occur in the bathroom whereby I was getting a strange tingle on broken skin while washing my hands in the bathroom. It felt faintly electrical so I switched the electricity of at the breaker and lo and behold it went away.

The only place where electricity could have possibly have come in contact with water in the bathroom is the towel radiator. Pipes run around the bottom of the wall while any cables run around the top so I can't see any way it could be anything else.

I disconnected the element and again that cured it. I noticed in the process of doing this that touching the earth conductors of the incoming feed and the element cable produced a bit of a spark, also touching the incoming earth resulted in a little shock (live was isolated) which I guess is suggestive of an earth fault somewhere.

So, after some disconnecting of cables and doing some basic insulation tests with a multimeter, I think I've isolated the problem to the cable between the fuse box and the switches for the bathroom (bathroom is on a radial circuit).

Resistance between live and earth conductors measures about 15kOhm. Cable is disconnected both ends so should effectively be open circuit. Other cables do read open circuit in a similar test.

Before I start ripping walls apart to try and replace this cable, I just wanted to reassure myself I'm not being an idiot and this does sound like it is the problem?

Thanks,

J

 

[FrodoOne]

So, after some disconnecting of cables and doing some basic insulation tests with a multimeter, I think I've isolated the problem to the cable between the fuse box and the switches for the bathroom (bathroom is on a radial circuit).

Resistance between live and earth conductors measures about 15kOhm. Cable is disconnected both ends so should effectively be open circuit. Other cables do read open circuit in a similar test.

If accurate, that leakage resistance would indicate a leakage current of 16 mA when 240 V was applied, probably about half that required to operate a RCD or RCBO - which I hope that you have installed to provide protection on that circuit.

While you wrote "The only place where electricity could have possibly have come in contact with water in the bathroom is the towel radiator", I suggest that that the "tingle" which you received was due to you being in contact (direct or indirect) with the frame of the radiator and the water flow (from a metal pipe) was actually at Earth potential.

However, while there may have been the leakage of 16 mA, you should not have felt anything if the Earth conductor connected to the radiator was properly earthed at the Consumer Unit - since, with only that small current and the RCD/RCBO not operating, there should not have been any significant voltage drop along the Earth conductor.
Therefore, I suspect that you may have a "leaky" cable and had a faulty Earth connection at the CU, or at some point along the circuit from the CU.

 

[bernardgreen]

An electric shock or severe tingle requires two points of contact with the body and these points have to be at different potentials.

Standing on a wet floor and getting a shock from a pipe or tap . Maybe the tap is properly Earthed and the water on the floor that is, due to a fault, is Live due to water or dampness being in contact with a Live item.

Water touching a damaged cable or in contact with metal in a junction box are two examples of how a wet floor can become Live

 

[John D v2.0]

Is your main bonding in place between the main earth terminal and any incoming metallic services? Also is there continuity between the main earth terminal and the radiator casing?
Be careful when testing and disconnecting things as if there's a fault and you effectively cause another by disconnecting things then it could be dangerous. In the worst case there could be a disconnected neutral somewhere and all the current could be flowing via the main bonding. Or if there's nothing to bond, the house may be floating at a higher voltage

 

[davelx]

If accurate, that leakage resistance would indicate a leakage current of 16 mA when 240 V was applied, probably about half that required to operate a RCD or RCBO - which I hope that you have installed to provide protection on that circuit.

Note that it is entirely possible that the OP does not have a modern consumer unit, and thus no RCD protection. (My neighbour's house still has a 4-way Wylex rewireable!).