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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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    Old farm house, extension, dedicated PME supply? First I would measure Zs at the fault point. 

    And confirm that it was low enough to be PME, not just some cable running off of a possible TT supply from the old part of the building.

    Having no connection back to neutral via the MET or being TT would explain the reason for the circuit breaker not tripping even though there seemed to be a reasonably good connection to earth. If the MET doesn't actually have a good connection to earth then the resistance could easily prevent the circuit breaker from ever tripping.

    Sold by an electrician and no RCD's? If that was not a very long time ago, then it's time to expect more problems. A test in 2021 and no records? that should be cause for concern. The owners should have been given paper copies at the very least.

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  • 0

    Old farm house, extension, dedicated PME supply? First I would measure Zs at the fault point. 

    And confirm that it was low enough to be PME, not just some cable running off of a possible TT supply from the old part of the building.

    Having no connection back to neutral via the MET or being TT would explain the reason for the circuit breaker not tripping even though there seemed to be a reasonably good connection to earth. If the MET doesn't actually have a good connection to earth then the resistance could easily prevent the circuit breaker from ever tripping.

    Sold by an electrician and no RCD's? If that was not a very long time ago, then it's time to expect more problems. A test in 2021 and no records? that should be cause for concern. The owners should have been given paper copies at the very least.

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