Mains electric shock from plastic light switch - no fault found by electrician - what next?

[jimster99]

Hi all! This is my first post and I have registered to ask for some help with troubleshooting an electric shock I got from a plastic light switch outside a bathroom today.

I turned the switch off with my left hand and got what felt like a mains electric shock through the switch into my left arm. It had the distinctive "throbbing" feel of mains electricity and I felt it mainly through my left arm and left torso. I pulled my arm away and my rib cage still feels a little sore this evening. It was definitely not a static shock. The apartment has an RCD box which didn't trip.

The light switch itself is plastic but has metal screws (although I don't think I touched them). I was wearing slightly damp socks on a thin carpeted floor and my hand was possibly a bit damp from washing my hands in the toilet so my resistance was probably relatively low.

An electrician has now been to visit and said he couldn't find anything wrong and he seemed to suggest I couldn't have had a shock. He very happily touched the switch and it was fine. The wires in the switch appeared to be screwed in properly and the same in the light. The switch is mounted in a metal frame but he couldn't find any live voltage where there shouldn't be with his two-pronged multi meter. He did suggest that a more thorough check of the property and this is being scheduled.

This may be unrelated but in the morning before the shock my wife had noticed that the light in the bathroom controlled by the switch (which is a ceiling mounted multi-LED type) was pulsing on and off approximately once a second when switched off. When turned back on it was working fine but then still pulsing when switched off. The light then started working normally again so we thought it had cleared up.

Any ideas as to what can possibly have caused this? I didn't imagine it but with the electrician not finding anything wrong, I am flummoxed! Note I am handy with a multimeter but only a hobbyist and I normally steer well clear of working on mains electricity.

Pics of the light switch are below:

 

[jimster99]

Now I would take the fitting down and examine the wiring underneath.

Jimster99 - if you feel confident first turn off both red main switches and all the circuit breakers and then remove the fitting securing screws while taking the weight of the fitting. Then take a photo of what you see of the wiring above the fitting especially of any connectors. Then carefully put everything back in place, turn on mains switches and the circuit breakers.

Thanks again Marconi, will do this during the course of the current week!

 

[Lucien Nunes]

Returning to the possibility that the shock was received from the switch mounting screws, which indicates that the CPC (Earth) conductor of the circuit is not earthed, I was thinking about the severity of the shock received. The most likely cause in that case would seem to me to be loss of connectivity at the consumer unit, rather than a local problem to the bathroom light.

If the CPC is disconnected locally it will float, but absent another fault would not collect enough leakage current from the nearby cables to give a heavy shock. To do that it would likely have been connected to the earth bar in the CU, while the CU was disconnected from main earth and any bonding due to an intermittent connection. Just possibly, loss of connectivity between all or most of the lighting circuit CPC and CU earth bar (which would leave the entire circuit's capacitive leakage accessible at all points) would be enough to deliver a heavy shock.

The above scenarios of intermittent earth connections should be fairly easy to locate by inspection and testing, unless one is very unlucky and there is a concealed intermittent e.g. where a cable is partially cut through, that is at the moment making very good contact and not detectable by unusually high resistance.

 

[Alla Musica]

LAP and BG are now well and truly on my avoid list

What went wrong with BG switches? Would love to know - I have one at home and I'm slightly worried

 

[timhoward]

What went wrong with BG switches? Would love to know - I have one at home and I'm slightly worried

Don’t over think this or over worry! They just don’t always last as long as other brands, especially if switching heavier loads.

 

[Alla Musica]

Don’t over think this or over worry! They just don’t always last as long as other brands, especially if switching heavier loads.

Aha, no wonder the 30-year warranty (just kidding)