earth rod info

Discussion in 'Electrics UK' started by bary80, 13 Apr 2011.

  1. bary80

    bary80

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    iv'e installed an earth rod in a garden. after nocking in two rods joint together i had an ELI of 13.6. i added another and now am getting OL on 20 ohms and 0 on psc. any ideas what im doind wrong.
     
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  3. flameport

    flameport

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    So what is the problem ?
     
  4. bary80

    bary80

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    well OL is a failed test isnt it and and i have no 0 as a psc reading.
     
  5. Lectrician

    Lectrician

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    What meter? Not sure what OL means.

    Flameport - I think he means he is getting a reading of "OL" when set on the 20ohm range on the meter - not that he is getting a reading of 20ohms.

    I would have been more than happy with 13ohms though - I would not have bothered or even dreamed of going further!
     
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  7. Adam_151

    Adam_151

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    IIRC, OL is what the kewtech kit displays for 'over limit'... so in the OPs case, greater than 20ohms and so he needs to change range

    Very good reading at 13ohms though, was that with the rod disconnected from all other earth paths?
     
  8. 1john

    1john

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    electrical work
     
  9. 1john

    1john

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    Why keep knocking rods in when you have such a good reading?
     
  10. ericmark

    ericmark

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    To test the earth rod with an earth loop impedance meter you are also testing the boards earth. The board is only required to have a reading of 21 ohms outside the installation so it is possible even with a perfect earth using an earth loop impedance tester the reading would still be 21 ohms.

    Only with the two test probes of an earth rod test rig can one really be sure of low readings being really what the rod is giving. Even then to get 8 ohms I was using between 4 and 8 rods at a gas receiving station where I sunk in 100's of rods.

    With all water pipes etc disconnected 13 ohms would be a great reading and if I was presented with those readings I would be uneasy as likely the water pipes etc have not been disconnected to get such a low reading.

    I would expect around 60 ohms in a domestic which is low enough to trip the 100ma RCD and likely still stable even in dry weather.

    If you want a reading below 30 ohms then don't use an earth loop impedance meter use the special earth rod test meter.

    I admit many look at the reading on the earth loop impedance meter with all bonding still connected and consider that it does not really matter if the earth is from the electrode, water, gas or any other metal work as long as it is there. In some ways that is correct. However we can't rely on water or gas and one month after testing the utilities may change the material the pipes are made of. So I always test the rod alone when doing an inspection report. However when doing other work then I will take the readings presented as correct if they seem to be what would be expected. Marked of course as "by enquiry".

    But only by measuring on regular basis does anyone know what to expect and I would think from comments bary80 does not know what to expect. I have installed many rods, but I don't remember installing or testing a single rod during my apprenticeship, or in college, we only did theory, so I can understand why an electrician would have problems with this.
     
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