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Electric shock through live apparently earthed metal face plate.

aligarjon

A friend asked me to check electrics at a house his daughter had just moved in to last Friday.  They had been getting shocks from a metal light switch so had been using their sleeve to turn it on and off can you believe.  He went round for another reason and touched it and got a nasty belt, his hand was still aching when i arrived twenty minutes after.  I popped one prong of my two prong tester on it and it buzzed to indicate it was live, i didn't confirm it was a full 230v as there wasn't an easy place for the other prong.                                                                                I turned the power off and removed the switch, it appears that one of the cores had scagged the south lug which hadn't been bent out the way.

 What confuses is me as to why the circuit breaker did not trip as it appears that it was a dead short although there was no blacking of the cable where it looks like it touched the lug, just a deep dent in the insulation.

 I confirmed the earth continuity as i initially thought that the earth had to be missing.There was also a fly lead.  The building is an old farm house although this part was in a newer extension with a sub-main and dedicated  CU.  there are no rcd's in the building.  The installation was apparently sold by an electrician, there was a nice inspection and test label at the CU dated Sept 2021 but no actual report that they know of.  

I have recommended they have the consumer units updated.   

It had a PME earth

Gary                                                                                               

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    First guess would be lack of an Earth loop - perhaps on the supplier's side rather than in the installation. How back 'back' did you check the continuity?

    It's not unknown for people to connect the Earthing conductor to the Earth terminal on the cut-out without checking that it's actually connected internally (and it's quite possible it isn't if the supply was intended to be TT - for a farmhouse that is plausible).

    Other question was what else were they touching at the same time (there must be something to create the voltage difference to give a shock)... the other possibility is that's live and the switch is Earthed.

       - Andy.

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  • 0

    First guess would be lack of an Earth loop - perhaps on the supplier's side rather than in the installation. How back 'back' did you check the continuity?

    It's not unknown for people to connect the Earthing conductor to the Earth terminal on the cut-out without checking that it's actually connected internally (and it's quite possible it isn't if the supply was intended to be TT - for a farmhouse that is plausible).

    Other question was what else were they touching at the same time (there must be something to create the voltage difference to give a shock)... the other possibility is that's live and the switch is Earthed.

       - Andy.

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