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Thursday debate BS7671 vs CoMCoP & Gas Safe

Sergio Fernandez

I was on FaceBook the other day a saw a meter box which had the gas meter removed.  They had connected an Earth/Bond cable to the 2 ends of the remaining now defunct gas pipes.  It seems this is standard practice when a Gas meter is removed.

Several questions and points to discuss
If there is NO earth clamp on the customer side of gas meter within the permitted length of 600 mm of the outlet union of the meter; and before any branch (tee) in the pipework should the Earth bond be installed by the Gas meter engineer?  The practice of just putting the bond across where the gas meter used to be without proper consideration means that a healthy Ze and Zs could be compromised.  Additionally they could accidentally introduce potential into the building.  Do the Gas meter engineers test to see if this is an Extraneous conductive part?

Scenario 2
There is an Earth Bond of customer side of meter do the Gas meter engineers check with a clamp meter to see if there is mA or Amps.  mA probably being acceptable but Amps not acceptable.  Consider a PEN fault




As always please be polite and respectful in this purely academic debate.




Come on everybody let’s help inspire the future.

  • Unless of course the gas supply has the insulating unions required under the latest ENA guide 12, and most notable by their total absence from any real installation.

    However the rules say

    "5.2 Earthing terminal
    5.2.1 Provision of earth terminal
    PME earth terminals can be offered to consumers unless there are reasonable grounds to believe either:
    - their earthing installation is not designed to BS 7671.
    - or
    - the type of installation is not suitable for PME. (See Section 6 for examples where it may not be possible to provide a PME earth terminal).
    Where a metallic gas service is provided to a consumer’s premises with a PME earth terminal, an insulated insert should be fitted in the gas service."

    Mike.

    PS wiring matters did a thing on this you know... https://electrical.theiet.org/media/1189/insulation-inserts-in-metallic-gas-service-pipes-to-consumers-premises.pdf

    when that article came out, for a giggle I did try and buy an insulating insert at the local place that does gas stuff, and I would have had more success and less funny looks if I had been asking for tartan paint !!

  • If there is no protective bonding conductor within 600 mm of the meter, is there one at all?

    If there is, and the meter is removed, assuming that the gas pipe is metallic (mine still is) the stump is now the extraneous CP so the bonding needs to go to that. A link across the gap will achieve that, so it seems to be a sensible default practice.

    I trust that a warning notice was installed. Innocent

  • in reply to mapj1

    Might be worth a read.  Not sure if this is still current

    https://registeredgasengineer.co.uk/technical/technical-bulletin-102-2/

  • in reply to AJJewsbury

    What would happen in a fault scenario ie Broken PEN in the street.  Now that link allows the potential to rise inside the instalation. 

  • NHBC Guidance.

    www.nhbc.co.uk/.../protective-equipotential-bonding-peb-of-gas-installation-pipework-new-june-2020.pdf

  • in reply to Sparkingchip

    On Page 2 it states

    Where there is any doubt on whether PEB is, or is not, needed a continuity measurement should be made of the resistance between the conductive part (gas pipework) and the incoming earthing conductor in the dwelling. The resultant figure will indicate whether PEB is required

    It might be beneficial to state the required continuity measurement.  There is also no mention of using a clamp meter to measure for mA or Amps on the existing Earth bond on the customer side.  No mention of the possibility of PEN faults.  Maybe that document by the NHBC needs an update.  It also refers to BS 7671:2018

  • in reply to OlympusMons

    I wonder if they use and carry contact and non-contact voltage sticks?  Do they use clamp meter on the Earth bond to measure for mA and Amps?

  • What would happen in a fault scenario ie Broken PEN in the street.  Now that link allows the potential to rise inside the instalation. 

    As it would anyway if the property was downstream of the break (via the PEN conductor) or where the supplies are still metallic via the water bond (as gas and water will be bonded together in neighbouring properties). Main bonding should mitigate the danger whatever the cause or path - at least within the building.

       - Andy.

  • “As always please be polite and respectful in this purely academic debate.




    Come on everybody let’s help inspire the future”.

    Your emphasis on civility and the aspirational nature of everyones discourse is well noted. The collective esteem we all share for engaging in respectful dialogue is a testament to mine if not everyone’s mutual understanding of its significance.

    Well done Sergio for your continued enthusiasm to spark debate, hats off Thumbsup

  • in reply to AMK

    Thank you AMK

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