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Gas Pipe Bonding Question

Nigel Hoult

My house has a PME system, and there are bonding cables connecting ground on the distribution board to the water main and to the gas pipework immediately after the meter, which I believe is the normal arrangement.The gas meter is located in an attached garage.

When last tested and updated, the gas meter was the traditional metal type and the gas main was cast iron, so both of these bonding cables were effectively connecting the distribution board ground to earth. Since that time two things have changed:

1. The gas meter was replaced by a smart meter, which appears to be at least partly plastic; however, I imagine that the metal mounting bracket still provides connectivity between inlet and outlet. When this was done the installers attached a label saying that there appeared not to be equipotential bonding which I admit I ignored, since to my mind this was clearly present.

2. The gas pipe was replaced by a plastic one; however, this is threaded through the old cast iron one between the edge of the property and a metre or so short of the gas meter. This means that there is no longer an electrical connection between ground on the distribution board and what remains of the cast iron gas pipe in the garage.

My question is simply, does this pipe need to be bonded to the remainder of the gas installation (and therefore the distribution board ground)? On the face of it, a person in the garage could quite easily touch both that pipe and the other sde of the meter (or indeed any electrical equipment in the garage grounded to mains earth) which would suggest that such bonding might be required, but on the other hand they could equally well touch the fabric of the building instead of the gas pipe, which would suggest that it would not make any difference. Another factor is that the installation ground (in the event of a fault in the supply neutral conductor) now only has one route to earth rather than two, so its impedance must surely be higher, but again, is this something that matters since I don't believe it was ever measured?

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  • 0

    Thanks for the helpful replies. On looking more closely, I discovered that the relevant pipe is actually covered in plastic (I had assumed it was merely painted), and therefore is not an extraneous conductive part. The gas people have also attached a label saying that it is not to be used as an earth. Therefore, I think I will leave things as they are.

  • 0 in reply to Nigel Hoult

    If you are concerned about it and don't want to bond it another solution would be a small bit of boxing in around it so it can't be touched at the same time as the existing bonded pipework.

    Gary

  • 0 in reply to aligarjon

    I was thinking along similar lines. As there's hardly any metal exposed - and that which by all accounts must be metal still doesn't seem conductive - I think some tape should be sufficient

  • 0 in reply to aligarjon

    +1 for not bonding, but arranging the old metallic pipework so no metallic part of it can be touched (check too the cut ends, if it's plastic covered).

    It's not an unknown situation. In some circumstances the gas industry deliberately install insulating junctions (IJs) at gas meters - specifically to prevent diverted neutral currents (and possibly earth fault currents) from flowing through their pipework (historically there have been problems in places like blocks of flats where CNE cabling has been taken to individual flats). Bonding on the supply side of the gas meter, while logical from a BS 7671 point of view, would entirely default the purpose of the IJ.

    Note that the gas people have reservations about running gas pipes, especially supply side ones (which can't be routinely pressure tested), in building cavities and voids ... as there's a risk of an undetected gas escape building up to explosive levels, undetected, in such a confined space. Sometimes you see boxing-in with deliberate ventilation top & bottom - which I presume is to mitigate such risks.

       - Andy.

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  • 0 in reply to aligarjon

    +1 for not bonding, but arranging the old metallic pipework so no metallic part of it can be touched (check too the cut ends, if it's plastic covered).

    It's not an unknown situation. In some circumstances the gas industry deliberately install insulating junctions (IJs) at gas meters - specifically to prevent diverted neutral currents (and possibly earth fault currents) from flowing through their pipework (historically there have been problems in places like blocks of flats where CNE cabling has been taken to individual flats). Bonding on the supply side of the gas meter, while logical from a BS 7671 point of view, would entirely default the purpose of the IJ.

    Note that the gas people have reservations about running gas pipes, especially supply side ones (which can't be routinely pressure tested), in building cavities and voids ... as there's a risk of an undetected gas escape building up to explosive levels, undetected, in such a confined space. Sometimes you see boxing-in with deliberate ventilation top & bottom - which I presume is to mitigate such risks.

       - Andy.

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