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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

    I do have a concern about people considering "sheathed" ("insulated", or "plastic covered") metal parts that are buried in the ground, but later become connected to accessible metalwork in buildings, as not 'extraneous-conductive-parts'. Stones in the ground, and, depending on the plastic covering, water ingress, can render the metallic parts as 'effectively earthed' ... but this is not measurable during original 'erection' of the installation.

    I do also have concerns about the fact that main protective bonding is now only applied to buildings ... but not other installations (this has been the case for quite some time). It will cause more of a problem for installations such as water treatment, chemical processing/manufacturing plants (with outdoor installations) etc.

    I fully understand the issue regarding "how big a site are we talking about" vs "touch and step potentials" .. but if "rules" can be applied for HV, they can also be adopted for LV.

  • 0 in reply to gkenyon

    I do have a concern about people considering "sheathed" ("insulated", or "plastic covered") metal parts that are buried in the ground, but later become connected to accessible metalwork in buildings, as not 'extraneous-conductive-parts'.

    Agreed - and to add, that if the same part emerges into another building (or otherwise into another electrical installation) even if it's perfectly isolated from the general mass of the earth - then it's still likely to be an extraneous-conductive-part as faults in the other installation will may impose a potential onto the part (and hence into our installation) - via c.p.c.s to valaves/pumps etc even if the pipe isn't bonded.

    In the OPs case everything seem to point to it being extraneous.

       - Andy.

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  • 0 in reply to gkenyon

    I do have a concern about people considering "sheathed" ("insulated", or "plastic covered") metal parts that are buried in the ground, but later become connected to accessible metalwork in buildings, as not 'extraneous-conductive-parts'.

    Agreed - and to add, that if the same part emerges into another building (or otherwise into another electrical installation) even if it's perfectly isolated from the general mass of the earth - then it's still likely to be an extraneous-conductive-part as faults in the other installation will may impose a potential onto the part (and hence into our installation) - via c.p.c.s to valaves/pumps etc even if the pipe isn't bonded.

    In the OPs case everything seem to point to it being extraneous.

       - Andy.

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