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Thread: Earthing

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    Earthing

    Is the earthing of guttering, down pipes and metal roofing still compulsory
    when the main supply cable is underground? Or is this only applicable for overhead supply installations.
    Another question, most of the new plumbing pipe is plastic or pollycarb, so then it is not necessary to earth all taps anymore.

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    Quote Originally Posted by TECHNICIAN 810 View Post
    Is the earthing of guttering, down pipes and metal roofing still compulsory
    when the main supply cable is underground? Or is this only applicable for overhead supply installations.
    Another question, most of the new plumbing pipe is plastic or pollycarb, so then it is not necessary to earth all taps anymore.
    you would need to look at the application...but you are on the right track...if the overhead line has been replaced with airdac or an underground cable the requirements would change.

    you cant earth plastic...but also look at the installation as a whole because in some cases the hot water pipe is still copper...but if the cold is plastic then you cannot bond the geyser.

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    Thanks Murdock, the application is actually the world class developer Century property developments. None of the houses on the entire estate have earthing on gutters or taps, all piping is poly C, nor are the DB boards labled DB 1 Fed from.....
    Sub Street boxes are numberd and labled.

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    If the plumbing pipework is all polycop then you can't bond the pipework and I wouldn't bond the taps. As far as I know though polycop (orange pipe) isn't rated for hot water use but I would check this with a plumber.
    If necessary, running an earth bond to the roof or gutters should be easy as all new developements require an earth bar in the loft for other services so you should be able to run a wire from that for gutters, roof, TV antenna, satalite dish etc.
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    if its not an overhead supply then its not necessary to earth the gutters or roof.
    what are the specs of the earth bar in the roof? a 2,5mm wire with a bolt through the rafter?
    i see cobra make this white polycop that can be used for hot water .very thick wall and very easy to work with.

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    This is the only thread for earthing so I would like to use it for my example.
    Went to a house yesterday where the guy was getting shocked when touching the gate motor bracket, fridge and anything else "earthed"
    There was no municipal earth supply but I found a connection to an earth spike from the earth bar and a second connection between earth and neutral, seems ok?
    Well it is as long as neutral is neutral but in this case the municipal supply had been reversed and the neutral was now live. Seems the earth spike was not as effective as required and the house was alive.
    To make a mistake is human, to learn from that mistake is knowledge and knowledge is strength.

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    Quote Originally Posted by Leecatt View Post
    This is the only thread for earthing so I would like to use it for my example.
    Went to a house yesterday where the guy was getting shocked when touching the gate motor bracket, fridge and anything else "earthed"
    There was no municipal earth supply but I found a connection to an earth spike from the earth bar and a second connection between earth and neutral, seems ok?
    Well it is as long as neutral is neutral but in this case the municipal supply had been reversed and the neutral was now live. Seems the earth spike was not as effective as required and the house was alive.


    What was the earthing arrangement, TN-C-S, TT? Can you post a couple of photos? What earth impedances did you test?

    First question is why didn't the RCD (earth leakage breaker) in the DB trip?

    Are you sure the supply was reversed? It's not a common fault...in fact it would reek of saboutage or willful damage. Also with an incoming supply reversal the live supply would be directly to the earth rod as well as any other parallel earth paths through the building services etc so the second question is why didn't the MCB in the council cabinet trip?

    Are you sure it wasn't a high resistance or missing supply neutral rather than a complete supply reversal?? This could also cause many the symptoms you describe.

    To receive a shock from the chassis of an appliance you need multiple faults to occur simultaneously. (1)There is an insulation fault that allows a leakage current to flow between the live conductors and the chassis. (2)The earthing is inadequate which allows the chassis touch voltage to rise. (3)The RCD is faulty
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    It had me stumped as well for an hour or so.
    The E/L tested at 25mA ok, but did not trip unless the button was pushed.
    I disconnected the incoming supply completely and had 220v between live and neutral, 220v between neutral and earth and nothing between live and earth.
    All I can conclude is that the earth rod is not effective and I cannot say why the E/L did not trip
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    just a thought, assuming the spike passes at 20 ohms,if there is direct live on to it you would only have 11 amps.not enough to trip the main switch.if there is a good suppliers earth the current should be more. so the spike might be fine.

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    Yep, if it was a TT installation and there were no parallel paths through the bonding to other services then a 20 ohm spike wouldn't be sufficient to trip the MCB on the incoming power. You'd need an earth impedence of less than 3 ohms. That said I've never seen a domestic installation on a TT earthing arrangement but it might be because I rarely work domestic and only in my area.

    The worrying thing for me is the incoming supply reversal. This should never happen under any circumstances.
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