Live wall back boxes!

Discussion in 'Electricians' Talk' started by Triman, Oct 25, 2014.

  1. Triman

    Triman New Member

    I have recently visited an old stone property to install a porch light. Cabling from 70s. I discovered the downstairs light circuit wall boxes are all live. I get a shock when I touch the screws. The householders children have been complaining for a while apparently. Im getting a reading of 230V from line (live) switch wires to Metal boxes, as you might expect. So there appears to be earth continuity. However, I also get 230V from Wall box to earth on ring final. (One box gives 30V only). Lights work fine. The circuits are taken from a modern CU with RCD. RCD is not tripping to this fault. I have switched off the circuit, taped over the screws and will continuity and IR test ASAP. The load is low due to low energy bulbs and LEDs. I’m thinking NE fault, as anything else would trip the breakers or RCD. Any thoughts appreciated.
     
  2. Bazza-spark

    Bazza-spark Screwfix Select

    Firstly let me ask you when you say live switch wires are you talking about the live feed to the switch or the wire from the switch to the light?

    Secondly a neutral - earth fault should also trip the RCD.

    Thirdly, taping over the screws is only part of the issue. What happens when you check the taps and copper water pipes? If the pipes are live as well then there is serious risk of electrocution and the installation needs to be made safe immediately and cannot be left as it is.

    Kind regards
     
    FatHands likes this.
  3. JP.

    JP. Screwfix Select

    Sounds like the family should get out of the property until it is electrically fixed - its a C1..phorrrrrrrrrrrrrrrrr
     
  4. JP.

    JP. Screwfix Select

    ''Mum mum - I was in the bathroom and a snake bit me''

    The above translates to - mum mum I was in the bathroom and I touched a bare pipe and it gave me a shock.


    It just goes to prove what can happen under a C1.
     
  5. joinerjohn1

    joinerjohn1 Screwfix Select

    Depends who the "snake" belongs to. :p:p:p:p
     
  6. seneca

    seneca Screwfix Select

    Sounds like no main earth, what's the Ze like?
     
  7. flateric

    flateric Well-Known Member

    Sounds like this one could end in tragedy :(
     
  8. Caddy

    Caddy Active Member

    Im not sure how you would get 230v between live to the back box (assuming back box is earthed) and then 230V from earthed back box to the ring final earth.. one of those combinations should read nearly 0v as they would be near the same potential..

    Out of interest have you taken a reading between the metal back boxes and the ring final earth with the board turned off?
     
  9. Bazza-spark

    Bazza-spark Screwfix Select

    Caddy, the OP's question doesn't make complete sense to me either. My concern is if his readings are correct things could be very dangerous, but I am also doubtful about the readings.

    His lack of responses make me wonder if he is genuine.
     
  10. flateric

    flateric Well-Known Member

    Perhaps he has fried whilst operating one of his switches and can no longer reply :)
     
    Bazza-spark likes this.
  11. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    PIR the lot, at least its on paper it needs rectification,

    Chuck the hot brick back in their lap
     
  12. Triman

    Triman New Member

    I'm still alive.. Thanks for your thoughts. I checked all light switch screws on the light circuit to a Ring final earth for Voltage. All but one was 230v. Nothing live with circuit dead. No issues with other circuit wall boxes. I will carry out some dead tests, following some of your suggestions and report back. The new board test results check out and is quite recent but theres been some DIY changing of light switches since.
     
  13. Caddy

    Caddy Active Member

    If you are getting 230V from the light switch boxes to the ring final earth then you should be getting 0v (or there abouts) between the Light switch boxes and the lives at the switches.

    Best to check if you get any voltage readings with the board turned off and check R2 continuity to all the switches.

    I had a similar problem at a house once, they had 230V L-N 230V E-N but 400v E-L.. Tunred out to be a fault in the house next door (old voltage trip not working) and the fault was going down the earth spike and back up into the neighbours house causing all the earth's and pipework to be 230V.

    in your case the only thing i can think it may be is a broken earth and possible a damaged live - Earth causing the earthing in the circuit to be 230V from the broken point onwards, but as i said that would cause the reading between the lighting circuit lives and earthing at the boxes to read 0V
     
    FatHands likes this.
  14. seneca

    seneca Screwfix Select

    Are you taking these voltage measurements with a high impedance multi meter? If so you are likely to be getting very inaccurate results. (induced currents etc.)
     
  15. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Has the RCD been tested for trip with test button?

    Mr. HandyAndy - Really
     
  16. Bazza-spark

    Bazza-spark Screwfix Select

    I don't suspect the RCD. It is only the downstairs lights. At the moment the readings don't make sense unless the testing is switch wire to earth with the switch in the off position and an earth fault on the live supply. That would render the boxes live measuring through the lamps especially if as Seneca says it is with a high impedance meter. Something like an Avo 8 may show lower voltages and be more representative.

    The only thing I can think at the moment is that there is a phase to earth fault somewhere with the earth to the CU broken so preventing the RCD or MCB operating.
     
    FatHands likes this.
  17. retiredsparks

    retiredsparks Super Member

    Had these in my box for the last 43 years.
    RS DRUMMTL20.jpg
     
  18. FatHands

    FatHands Well-Known Member

    When i was an apprentice i was always told to use a test lamp and then when everything went electronic it was meters only.
     
  19. retiredsparks

    retiredsparks Super Member

    Fats, sometimes you need to get the basics...and then work from there. There is no arguing with a pygmy lamp...lol....416 to 230 nominal.
    Rs
     
    FatHands likes this.
  20. FatHands

    FatHands Well-Known Member

    indeed :)
     

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