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Gas pipe electrode

lyledunn
The DNO earth was lost in a supply to a private club premises so an EICR required for licensing purposes could not give a satisfactory designation. The DNO move at the same pace as a dead slug so it was decided to TT the premises. Contractor installed all the necessary equipment. The electrode reading is 120ohms. However, the gas pipe shows just over 1ohm. Nothing else connected to earth,

is this an issue?
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    Morning Lyle


    Firstly the gas pipe cannot be an earth electrode see 542.2.6. If your 120 ohm electrode meets the requirements of Table 41.5 then happy days.

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    I imagine the gas pipe is bonded to a better earth in some neighbouring property.


    But if it is changed for plastic you have not removed the only means of earthing, so the system is safe.


    I'd say OK, despite the fact that the 'not the main earth' is better than the official one and not that unusual for a TT system, with a metal gas or water main.

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    John Peckham:

    Morning Lyle


    Firstly the gas pipe cannot be an earth electrode see 542.2.6. If your 120 ohm electrode meets the requirements of Table 41.5 then happy days.

     




    Oh I know that John but no matter what you want to call it, the earth fault current won’t care. So the very exact requirement of said regulation is being met but of course any intention behind it, which presumably relates to explosion risk due to currents flowing on the pipe, whether fault or diverted, is clearly not being met. 

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    John, sorry good morning to you too!
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    mapj1:

    I imagine the gas pipe is bonded to a better earth in some neighbouring property.




    If the gas pipe were simply a very good electrode, all well and good, but if the neighbour is still connected to the DNO's earth, which might be PME, do we not have a problem?

  • 0

    Chris Pearson:




    mapj1:

    I imagine the gas pipe is bonded to a better earth in some neighbouring property.




    If the gas pipe were simply a very good electrode, all well and good, but if the neighbour is still connected to the DNO's earth, which might be PME, do we not have a problem?


     




    A matter of ensuring that the main equipotential bonding is in place I would say. 411.3.1.2.


    Z.

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