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Dodgy wiring? Got a rather nasty shock tonight :(

Discussion in 'Electrics UK' started by garmcqui, 29 Nov 2018.

  1. garmcqui

    garmcqui

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    Just moved into a ‘new’ (18yrs old) house, and am decorating one room at a time. Went to change a socket tonight, turned off the 32A upstairs sockets MCB, as per the labelling on the consumer unit (photo attached). Unscrewed socket, went to disconnect the live and *ouch* - got a hell of a kick (screwdriver hit the wall on the opposite side of room).

    3A9F0E0C-C8E4-44B7-A6A5-392199F7E52A.jpeg

    Before anyone says it, my fault entirely - should have tested the socket was off before proceeding.

    So after I’d thanked my lucky stars, and my heart rate had returned to normal, I did a bit of investigating and it turns out that half the upstairs sockets are actually on the 16A “Immersion” MCB.

    The other thing worrying me is that the RCD did not trip when I got the shock - should it have?

    We had an EICR done before moving in, which came back as satisfactory, with a few recommendations (see photos).

    1B5ACBCA-2AC2-46B3-875D-6920AA3633BB.png F3F6070D-2916-415A-9F3B-DB9A9A7EF2F0.png FC0D5A40-DD3C-4F85-8124-0F4490BAFDCD.png

    So...is this normal, and should anomalies like this have been picked up in the EICR?

    Other electrical things I’ve found which are strange are...

    ... the “cooker” MCB seemingly does nothing, the electric oven is on the “downstairs sockets” MCB. Is this normal? Just to me a 3kw oven on the same ring as a washing machine, tumble dryer, dishwasher and kettle seems a little excessive?

    ...the garage sockets and light is fed off a spur from a socket in the living room.

    Thanks
     
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  3. AndyPRK

    AndyPRK

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    It sounds ok.
    Maybe the rcd should have tripped so that is worth investigation. Does the test button trip it?
     
  4. JohnW2

    JohnW2

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    That depends upon what else you were touching when you touched the 'live'. If it was the neutral then, no, the RCD would not trip. On the other hand, if you were touching something 'earthed' then the RCD should have tripped IF the current through you was at least 30mA. However, that may not have been the case - a shock of, say, 25mA is pretty painful and frightening.

    However, as has been said, it might be worth getting the RCD checked - or, at the very least, make sure that it trips when you press the test button.

    In any event, I'm pleased that you survived the experience and, as you admit, learned the lesson.

    Kind Regards, John
     
  5. JP_

    JP_

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    I know very little about electrics, and that is why before doing anything I turn off all the power, then still double check the socket is not live in a very OCD way (how could it be?!?) by plugging something in, then double check other things are off, then check I really turned the right main switch off, then do what I need to do. I probably look mad while doing all this, but have not blown myself up yet. I always take loads of photos of everything, just in case it doesn't work afterwards, so I can put it back how it was.

    My electrics seem a bit weird, but all tested and signed off. Lots of spurs, I think radial circuits. Junction boxes under the floors etc.
     
  6. AndyPRK

    AndyPRK

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    A simple way is to leave an applinance plugged in and on, then turn the power off.
    If the appliance is off when you return, its a good start!
    But also double check
     
  7. garmcqui

    garmcqui

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    So, a 16A mcb on a ring final (at least I assume the upstairs sockets are on a ring final) is ok?

    The house did have a gravity fed hot water tank, with immersion, but this was done away with in 2012 when a combi boiler was fitted. So just curious why the immersion circuit is now being used for sockets. Hmmmm

    Also, oven on sockets ring - still ok? Won’t a 32A mcb trip if washing machine, oven and dishwasher are all on (fairly typical for a Sunday afternoon, for example), and someone goes to boil the kettle?
     
  8. AndyPRK

    AndyPRK

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    Check all bedroom sockets.

    I bet some will be on 16 others on 32.

    Ovens don’t take a lot

    Hobs plates should be on 32. Do u have Gas hob
     
  9. EFLImpudence

    EFLImpudence

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    16A is plenty for upstairs. No point having a 16A ring so perhaps it's a radial.

    Perhaps they separated upstairs and made it a radial.

    If you had the immersion removed then it isn't an immersion circuit, is it?

    Yes, nowadays there are lots of ovens that just plug in to the socket circuit.

    Might do. Has it ever?

    As with another thread in which the householder was unhappy with the arrangements, all that was wrong was the labels on the consumer unit.

    Check what goes off with each MCB and make the labels accurate for the future.
    Labels don't alter circuits.
     
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  11. plugwash

    plugwash

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    Nothing forbids having sockets on a 16A MCB. It should at the very least be labelled properly though. Also if there is still actually an immersion in use on that circuit you should think about what else you plug into those sockets.

    All depends on the path the current took. A RCD will detect an imbalance between live and neutral. If the current went to earth then it should trip, but if you touch both live and neutral with your body isolated from earth (not a difficult thing to do when changing a socket indoors) you get a shock and the RCD doesn't see anything out of the ordinary.

    Items 1,3 and 4 on the the list of 4 reccomendations seem to just be stuff about newer versions of the regs, I wouldn't be unduly worried about them. Item 2 strikes me as very strange, on a TN install there should be no need to rely on RCDs for "fault protection".

    As for the item on it's own reccomendation list that could just be the type of cable used. 1.67 is the expected ratio for modern 2.5mm² T&E but other cable types can be different.

    There seems to be a mistake in the circuit schedule, fields that only make sense for rings are filled in for the "immersion" circuit but not for the downstairs ring.

    I think it's pretty normal to find "surprises" when taking over a building. Any documentation you do get is likely to be outdated and/or fragmentary and non-intrusive inspections can easily miss stuff.

    For better or worse an EICR is not a thorough investigation of the entire installation. Some inspections are done, some measurements are made but many anomalies will slip past.

    Looking at your picture it seems someone has made a half-assed attempt at scribbling out the word cooker.

    I would be tempted to do some digging to see if said cooker circuit still exists and if-so what state it is in.

    Well 3KW or below ovens can be plugged into a normal socket just like any other normal domestic appliance.

    In practice it's normally ok, you might peak over 7.3KW but you are unlikely to sustain that kind of load for long enough to actually trip the breaker or damage the cables. Remember most domestic appliances have thermostats, they aren't continuously guzzling max rated power all the time they are in use.

    Is it a fused spur? if so then it's acceptable. If it's not fused then you should at the very least add a FCU in line to protect it from overloading.
     
    Last edited: 30 Nov 2018
  12. JohnW2

    JohnW2

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    Kind Regards, John
     
  13. securespark

    securespark

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    Perhaps I have missed this flicking through, but the EICR states there is only one point on the immersion circuit.
    Surely this is wrong and puts into question the rest of the report?
     
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  14. garmcqui

    garmcqui

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    This is my concern. Hmmm

    Also @ plugwash - thank you for taking the time for such a detailed reply.
     
    Last edited: 30 Nov 2018
  15. garmcqui

    garmcqui

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    Ok so did a bit more digging, and it turns out that, with everything switched off, switching on EITHER the 32A upstairs sockets mcb OR the 16A Immersion mcb will energise all upstairs sockets (as well as the old immersion switch in the airing cupboard).

    The term WTF comes to mind!

    Obviously there’s something connected somewhere that shouldn’t be - but where would that likely be, inside the CU?

    Behind the old immersion switch there are two 2.5mm t&e’s, both connected to the “feed” side, nothing attached to “load”. With either breaker on, one of the live wires is at 230v and the other at zero. Wouldn’t the immersion circuit have been a radial? Is yes, where does this other cable go to/come from?

    0FF4C265-6EB7-4E56-A0C5-FBC763298CC6.jpeg FAB100A5-C45B-4DEA-8042-6331B0C911E7.jpeg
     
    Last edited: 30 Nov 2018
  16. oldbutnotdead

    oldbutnotdead

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    Oops. Good odds someone at some stage (possibly when doing the EICR) has mistakenly swapped 1 leg of the RFC onto the old immersion heater MCB in the consumer unit. V poor.
    Bit of cable tracing is going to be required- power off, lid off consumer unit, identify actual T & E pairs, determine by low voltage metering which bit of T & E goes where (easiest to ID initially will probably be the immersion heater pair)

    EDIT Good odds there's a socket (maybe in the loft) hung on the old immersion heater circuit
     
  17. AndyPRK

    AndyPRK

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    oops.
    Someone doing the EICR you think....

    Leave one of the two MCB's off for now then
     
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