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Small voltage on ground wire

Discussion in 'Electrics UK' started by Moony8, 9 Nov 2019.

  1. Moony8

    Moony8

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    Hi

    I have just been changing some sockets in my conservatory.

    My consumer unit has two banks on it. This circuit was on a secondary bank (i.e. not the one with the main switch) and is protected by an RCD.

    I had the individual circuit turned off via it's breaker, but left the rest of the bank on. Confirmed no voltage on the circuit from the live/neutral and stated to work on it, however when I was trimming the wire back, the RCD on the secondary bank tripped. The primary bank remained live.

    I thought this was odd but continued to work on the circuit, but I then got a mild shock when I touched the wires.

    I tested the wires again using the circuit tester and this time checked the earth wire. The live and neutral were still reading 0 volts, however the earth was reading 33 volts.

    I turned the main bank off at the main switch and checked again - this time zero volts on the earth.

    I fitted the new sockets and turned both circuits back on. Everything seems to be working fine and the new sockets work - but i'm a little worried that this isn't normal.

    I did have the consumer unit relocated and replaced last year, but everything tested fine as far as I know and there has been no further work on the electrics since then.

    All of the wires are bundled closely together into the consumer unit. Could the reading on the earth be down to an induced current. Is it something I need to be worried about?

    Thanks
     
  2. flameport

    flameport

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    What are you using the measure the voltage, and when you have 'earth was reading 33 volts' what was that relative to?
     
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  4. Moony8

    Moony8

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    I was using a multi-meter. I measured it relative to one of the other wires - live or neutral, it didn't matter, it gave the same reading.

    Live to neutral gave zero volts.
     
  5. John D v2.0

    John D v2.0

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    That always happens, turning off the mcb only isolates the L conductor, but the rcd detects imbalance on neutral as well. Since neutral has a current flowing in other circuits outside that rcd it can have a potential difference. Shor it to earth creates a current neutral and earth which trips the rcd.
    You should really isolate all conductors which carry current before working on a circuit, ie L and N,
     
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