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Would my new dual RCD DB pick up this fault...

Discussion in 'Electrics UK' started by MattB83, 16 Nov 2020.

  1. MattB83

    MattB83

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    Brief background...

    Over the summer I started getting bad (i.e. burnt and drew blood) shocks from 3 light switches.

    Electrician came around and identified fault - said a faulty wire was causing voltage in earth and changed the wire, (making a horrific mess in the process) but also changing the chrome fittings to plastic. I don't want to be too critical of the guy because he was really nice, but he did a few other things in the house e.g. got me to unboard my whole loft which he then said he'd misread his testing equipment.

    Anyway after posting a pic of my old DB with old wired fuses on this forum I was told to upgrade promptly which I did, using other electricians who came highly recommended. I was told that the old board had RCD protection so would pick up earth faults however in the case of the light switch issue the fault wouldn't be picked up because it was a case of a problem between a wire and a switch.

    So my question is:
    Would my new DB pick up this fault of it was still there? I'm wondering if the fault is actually fixed or if it could just be hiding behind the plastic switches which wouldn't be as likely to give me a nasty shock. The electricians who installed the new DB gave me an electrical safety certificate if that is important info.
     
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  3. oldbutnotdead

    oldbutnotdead

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    If the fault was allowing you to be a conductor between live and neutral then no, your new RCD board won't trip.
    It is quite possible (depending on the age of the wiring) that the light fittings and switches are not earthed- or worse, the CPCs are/were connected at the fitting end but not at the CU end.
    So the backbox may not be earrhed but it shouldn't be live either- to verify you'll need a multimeter and a long wanderlead connected to a known good earth, then check for voltage between the various points.
     
  4. endecotp

    endecotp

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    So the original thread is here:
    https://www.diynot.com/diy/threads/electric-shocks-from-metal-light-switches.547973/
    but it’s mostly about the holes in the floorboards during the fix, not the electrics.

    I think we need to know a bit more about how you were getting the shocks from the switch.
    Certainly the most obvious faults would cause an RCD to trip (unless the shock current were below the RCD threshold). I’m not sure how you could get a live-neutral shock from a light switch, unless maybe the plate were neutral and the switch itself live.

    “Faulty cable causing voltage in earth” sounds like dim electrician not understanding what a floating earth looks like on a multimeter.
     
  5. MattB83

    MattB83

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    Thanks - the shocks were when I touched any part of the metal face plate on 3 light switches, all consecutive in the circuit if that's important - I maintained that they only happened when the washing machine was on but I can't think why this would happen as they were on different circuits so this could be rubbish - it was only ever me who got them. Although coincidentally the washing machine packed up a few weeks ago and was repeatedly tripping the RCD prior to being replaced.

    We have now spend about £700 as a result of this - although this included replacing the section of wire and then (taking forum advice) changing the DB so in the absence of any palpable problems (I've touched every screw and not a tickle) I'm just trying to decide if we need to do anything or just stop worrying?
     
  6. endecotp

    endecotp

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    We don’t know what the original problem that caused the shocks was, so it’s hard to comment on whether it will now have gone away.
     
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  8. MattB83

    MattB83

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    That's a good point thanks. I guess my question is really could any dangerous faults slip past a new DB which working fine and a safety certificate rather than second guessing what was going on originally.
     
  9. endecotp

    endecotp

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    Yes certainly.

    That would depend on how thorough the inspection was.
     
  10. MattB83

    MattB83

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    Thank you for this.
     
  11. Master of None

    Master of None

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    20 years ago when I bought this house and a new washing machine I was getting a shock touching the washing machine metal case. I called an electrician friend and he said check the earth connection on the socked. I removed the socket and none of the conductor terminals were tightened, they were just placed in the holes. After checking every accessory in the house I asked my friend what was causing the shock and he said if an appliance like that is not earthed you can get some voltage in the metal case.
    Is it possible for the OP that everything is connected to the earth circuit but it its self is not connected to earth?
     
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