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Continuity of earth test

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  • 19-01-2017 9:13pm
    #1
    Mikeyshragh
    Registered Users Posts: 92 ✭✭


    Hi a quick question.
    I'm getting a reading of 0.00 ohms on a lighting circuit when I'm doing the Rp+RE test. What am I doing wrong. And another test I was getting 1.34omhs on another lighting circuit. It's my first time testing and I'm trying to find out what I'm doing wrong. Please any help I would be greatful.


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    #2
    brightspark
    Registered Users Posts: 2,637 ✭✭✭brightspark


    How are you zeroing the meter?

    How long are the cables that you are measuring?


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    #3
    Mikeyshragh
    Registered Users Posts: 92 ✭✭Mikeyshragh


    brightspark wrote: »
    How are you zeroing the meter?

    How long are the cables that you are measuring?

    It's a fluke multifunction meter I have. I put the leads together and then press zero.

    The cable length is no more then 40 meters 1.5 single pvc earth. I'd have to measure it again. That's the one I got the high reading. As for the 0.00 reading it's all close to the board 10m 1.5 single pvc cable. Would the be normal reading to put on a test sheet?


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    #4
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    It sounds like either you haven't the leads nulled correctly or that you are possibly conducting the tests with low batteries within the test instrument which can often lead to unreliable and misleading results.


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    #5
    Mikeyshragh
    Registered Users Posts: 92 ✭✭Mikeyshragh


    Risteard81 wrote: »
    It sounds like either you haven't the leads nulled correctly or that you are possibly conducting the tests with low batteries within the test instrument which can often lead to unreliable and misleading results.

    I think I am zeroing it wrong. I haven't had it long and it's the 1st time doing a continuity of cpc. What is a reading where I would have to stop and invistagate if it was too high? I mean what would be a bad and good reading.


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    #6
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Mikeyshragh wrote: »
    Risteard81 wrote: »
    It sounds like either you haven't the leads nulled correctly or that you are possibly conducting the tests with low batteries within the test instrument which can often lead to unreliable and misleading results.

    I think I am zeroing it wrong. I haven't had it long and it's the 1st time doing a continuity of cpc. What is a reading where I would have to stop and invistagate if it was too high? I mean what would be a bad and good reading.
    If you look up the resistance of 1.5mm^2 copper conductors in milliohms per meter and divide by 1,000 (for Ohms per meter) and then multiply by ten you will have an idea of what you should be looking for. (Leaving aside temperature correction and other things.)

    You should make sure you have a stable reading before nulling with the crocodile clips touching fixed side touching the other fixed side (and not the spring loaded side to ensure proper connection). But as stated if the batteries are low many meters will be all over the place. Try fresh batteries if you haven't already.


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    #7
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Just to add to that, I notice that you are referring to an (Rp + Re) test, and therefore don't forgot to add the resistance of the phase conductor (1.5mm^2) to the cpc (if this is T&E it will be 1.0mm^2) before calculating the overall expected resistance. But you mentioned singles so I presume it's 1.5mm^2 phase and 1.5mm^2 cpc, so just double the resistance of the 1.5mm^2 to allow for both conductors.


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    #8
    Tuco88
    Registered Users Posts: 1,051 ✭✭✭Tuco88


    If I was you I'd just bridge Phase + Earth at the distribution board and measure at point. If it's a T + E multiple the value by 0.625 for Re value only. If the cpc is the same csa of the phases just divide the valve by 2.

    A good low reading(~0.1) 1 ohm would need investigation as Risteard81 stated appendix C will give you a good idea.

    Lower the valve better for EFLI testing later.


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    #9
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Tuco88 wrote: »
    If it's a T + E multiple the value by 0.625 for Rp value only.
    Just to correct that (with 1.5mm^2 T&E) that will give the value of Re, NOT Rp. (But that's (Re) the figure you'll want for maximum resistance of protective conductor if it's on that circuit.)


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    #10
    Tuco88
    Registered Users Posts: 1,051 ✭✭✭Tuco88


    Risteard81 wrote: »
    Tuco88 wrote: »
    If it's a T + E multiple the value by 0.625 for Rp value only.
    Just to correct that (with 1.5mm^2 T&E) that will give the value of Re, NOT Rp. (But that's (Re) the figure you'll want for maximum resistance of protective conductor if it's on that circuit.)
    Sorry typo.


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    #11
    brightspark
    Registered Users Posts: 2,637 ✭✭✭brightspark


    Can you post a photo of the mft settings?


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