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Thread: Shocking Voltage on Earth Terminal and anything bonded to it

  1. #1
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    Shocking Voltage on Earth Terminal and anything bonded to it

    Hello guys

    It's been a while since I posted anything...I need help asap. A new domestic installation has main building with Main DB and back rooms with Sub DB. Both buildings have 3kW geysers installed....
    Now a client has been complaining about getting shocked when taking shower on either one. Hot and cold water pipes are bonded to earth. Every extrenous conductive parts are bonded to Earth.

    I did insulation resistance test on Geysers elements... not down to Earth, a RCD is not tripping neither. I tested shower tabs with water on the floor and get 36Volts which I think its dangerous too. Isolated all other earth connections except for geyser, still got shocking voltage. Went on to test an Elevated Neutral Voltage on supply, with MCB off...got 32V on both buildings because B/rooms are looped on supply.

    LV Earthing System should be TN-C-S as I saw it on authority post (3phases with PEN conductor)
    I'm puzzled as to what would cause Voltage on Earth Terminal and anything that is bonded to it.

    I'd appreciate it very much if I could get help, or an insight guys. I'm really stuck

  2. #2
    Diamond Member AndyD's Avatar
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    First thing to do is isolate the supply before someone gets injured.
    Quote Originally Posted by Reginald View Post
    ........... LV Earthing System should be TN-C-S as I saw it on authority post (3phases with PEN conductor)..........
    Not sure what 'I saw it on authority post' means. Is the supply definately TN-C-S earthing arrangement? Can you actually see whether there's a CNE or single PEN conductor at the incoming supply point?

    Quote Originally Posted by Reginald View Post
    ........I tested shower tabs with water on the floor and get 36Volts which I think its dangerous too. Isolated all other earth connections except for geyser, still got shocking voltage. Went on to test an Elevated Neutral Voltage on supply, with MCB off...got 32V....
    What instrument/tester did you use to test for elevated voltage? How exactly did you do the test?

    A word of warning, assume all conductors including neutrals and PEN conductors are live until proven otherwise.

    If the supply is TN-C-S then it's probably PME. First thing I'd do is disconnect the incoming supply entirely and test for elevated voltage on the incoming supply PEN with a wander-lead to a known good earth (one that's been tested with earth impedance tester) such as building steel-work or a local earth rod that gives a good Ra reading of a few Ohms. There are certain supply faults that can cause dangerous elevated PEN voltages with TN-C-S supplies, these faults can result in parallel earth paths within the installation such as bonding wiring to carry high currents.

    Once you've proved the incoming supply is fine I'd test the integrity of the installation earthing. Do earth impedance tests from the furthest point of all the final circuits.

    Next is to prove the integrity of the main bonding and supplementary bonding across the geyser pipework etc. It's worth checking that the water pipework within the building is continuous copper and isn't interrupted in areas by plastic PEX pipe. Also test the taps and exposed pipework in the bathrooms with a wander lead to make sure their earth impedance is low.

    At this point you've proved the supply integrity and that the equipotential zone is in tact. I'd then run around with a wander lead to prove items such as metallic towel rails, window frames and other metallic items are classed as extraneous conductive and bond where necessary...especially in the bathrooms.

    Finally check that all circuits are supplied by the earth leakage breaker and ramp test it to ensure it's working correctly and IR test all circuits for insulation faults.

    Sounds like a lot of work I know, on a standard small-medium domestic installation it should take 2-3 hours and it's time well spent. It's easy to start running yourself around in circles with these types of faults, be methodical at least to the point where you've proved the supply, proved the equipotential zone and proved the circuits.
    Last edited by AndyD; 17-Jun-16 at 12:52 AM.
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    Gold Member Sparks's Avatar
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    My first test would be loop impedance. Just because there is an earth wire ate the property does not mean it is connected at the other end.

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    Full Member MullerR's Avatar
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    I also once came across a loose neutral from supplier side, causing taps to shock the tenants. It was a TNSC system.

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