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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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    Then there are some really nasty but hopefully rare possibles, like L-N reversal. The absence of RCD means that a crummy earth, say 10 ohms or more, perhaps from plumbing only,  may not actually operate any ADS, but it should show up in the electricity bill, and tingles from anything else earthed on the same side of the high Z.

    The meters will tell all. There may be a reason to replace the CU as well, but for this problem it would not be my first action. A high current L-E and L-N loop or PSSC test probably would. 

    I must admit 'sold by an electrician' does not cut much ice with me -some of the worst wiring I have seen is on home jobs by the trade -the old joke about the cobblers' children running barefoot is  sadly often true, in that some folk are too busy out earning to get round to doing the jobs at home so it becomes a pile of temporary patches of bits left over from that other job.. Do not get me wrong, not always all by any means, some are works of art,  but some you do wonder.(and if I'm brutally honest some of my home stuff is in that permanent temporary category too, especially the workshop.)

    Mike.

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    Then there are some really nasty but hopefully rare possibles, like L-N reversal. The absence of RCD means that a crummy earth, say 10 ohms or more, perhaps from plumbing only,  may not actually operate any ADS, but it should show up in the electricity bill, and tingles from anything else earthed on the same side of the high Z.

    The meters will tell all. There may be a reason to replace the CU as well, but for this problem it would not be my first action. A high current L-E and L-N loop or PSSC test probably would. 

    I must admit 'sold by an electrician' does not cut much ice with me -some of the worst wiring I have seen is on home jobs by the trade -the old joke about the cobblers' children running barefoot is  sadly often true, in that some folk are too busy out earning to get round to doing the jobs at home so it becomes a pile of temporary patches of bits left over from that other job.. Do not get me wrong, not always all by any means, some are works of art,  but some you do wonder.(and if I'm brutally honest some of my home stuff is in that permanent temporary category too, especially the workshop.)

    Mike.

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