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Bonding District heating Pipework,

Toby Knox

Hi

Everyone's favourite topic Earthing and bonding, Some background information, We have insulated metallic pipes going under ground to several blocks of flats. Each block has an intake room where the pipe work enters from the ground to the energy centre 1 kilometre away. Each block is at a different stage of construction with some being occupied. After spending some time on site I am yet to see any bonding in place for any pipework. I'm aware of the test for extraneous-conductive-part but due to these being occupied the pipework has meters, probes ect which creates parallel paths and the buildings in early construction phase only have temporary power with no reliable MET to test with. 

So many question how can I determine if the existing pipe work requires bonding and how can I test the new pipework with no reliable earth?

Attached is an photo of the intake room pipe work in the early stage of Construction.

Thank-you for any help on the matter.

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  • 0

    Is the pipework really metallic underground? Rigid pipework would be a pain to feed through ducts (presumably with 90 degree bends to arrive out of the ground vertically) - and all the pre-insulated tubing I've looked at has been plastic (usually PEX) which is much more flexible.

    Could it be what we're looking at is a transition from plastic to copper, that's then covered with thermal insulation?

    Test wise, the old school method would be to test against a temporary electrode (say a long screwdriver shoved into the mud outside) - even if it's off by a few hundred or even a thousand Ohms or so, it should still give you a sensible ball park reading, since you're looking for tens or hundreds of k Ohms.

       - Andy.

  • 0 in reply to AJJewsbury

    seconded. Plant a real extraneous conductive part in some real mud, and measure the resistance  to it - no need for power or a MET.

    Biggest risk of bonding here is that you are introducing links between the neutrals of substations that would normally never meet - 1km is a 'long way' in LV land. During thunderstorms and so on very large voltages may be induced as well as the risk of very significant diverted neutral currents in normal operation.

    Even if test show it is an extraneous conducting part,  serious consideration should be given to the use of insulating pipe sections and enclosures for the bit of visible metal as a safer  alternative to the normal 'bond everything in sight'. That might depend on the circulating fluid and its conductivity however.
    Mike.

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  • 0 in reply to AJJewsbury

    seconded. Plant a real extraneous conductive part in some real mud, and measure the resistance  to it - no need for power or a MET.

    Biggest risk of bonding here is that you are introducing links between the neutrals of substations that would normally never meet - 1km is a 'long way' in LV land. During thunderstorms and so on very large voltages may be induced as well as the risk of very significant diverted neutral currents in normal operation.

    Even if test show it is an extraneous conducting part,  serious consideration should be given to the use of insulating pipe sections and enclosures for the bit of visible metal as a safer  alternative to the normal 'bond everything in sight'. That might depend on the circulating fluid and its conductivity however.
    Mike.

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