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Gas bond in detached garage ?

aligarjon

Hi Guys.

I carried out an EICR earlier and am a little unsure of the bonding setup.  House built in 1982. Original wiring which is ok. 16mm tails/6mm earth. 6mm bonding conductors. 60 amp main fuse.

The gas meter is in the detached garage. About 2 meters from house. There is a 6mm gas bond in there at the gas meter that is clearly under sized as it has been taken from the 2.5mm supply cable for the garage power.

The gas pipe from the meter goes through a 4inch duct and pops up in the kitchen below the units next to the water pipe. Both are bonded there in 6mm. This area backs onto the garage so in reality 2 or 3 meters away if that is relevant. 

My question is is the bond by the gas meter actually required as it is outside anyway or will it potentially need upgrading.

My gut reaction is it is fine as it is. There is no water in the garage.

The supply pipe to the gas meter drops into the concrete floor and as far as I can chip the floor away looks steel, although I am only seeing threading nut connections before it is buried so may well be plastic.

Any guidance would be appreciated

Thanks.  Gary

  • 0
    aligarjon said:

    Yes best practice guide 4 Says if it is less than 6mm it should be coded as a C2. So implying an existing 6mm is OK. 16mm tails with a 6mm earth and 6mm bonding on a 60A fuse used to be pretty standard around here when I started in 1984.

    That doesn't solve the garage problem here mind :( 

    Agreed for PME.

  • 0 in reply to Chris Pearson
    Chris Pearson said:

    No, it is not IMHO.

    Isn't the reason for bonding as close as possible to the meter that it reduces the possibility of leaving a bond on a section of gas pipe which has subsequently been disconnected?

    The bonding in both buildings is necessary to conform to BS 7671. If it's PME, I agree that the cross-sectional area to the bond close to the meter is important, but that doesn't mean the gas pipes in the installation after the meter can't be further bonded. Especially in this case, the pipe goes underground, but still bonding needs to be applied "in each building" (Regulation 411.3.1.2).

  • 0 in reply to gkenyon

    The copper pipe will be about 30mm2 if it is 15mm copper, (Pi * diameter * 0.75mm)  and more like 55mm2 if it is  the more common 22mm OD, and assuming it is gas safety and use regs compliant, it will be soldered if there is any joint at all in the duct. You could poke in a bit of wire parallel to it in the fat pipe, but electrically whatever you do, it is the gas pipe that will always do the heavy lifting in terms of conducting as a parallel path.

    Its not dangerous, but it may well not meet the letter of current regs.
    Mike

  • 0 in reply to mapj1

    I agree. The other issue I have is that they have asked me to upgrade the consumer unit as it still has the original 3036 fuses and no RCD protection anywhere. So I will have an EIC that needs to comply even if there is a bit of 'wiggle room' on an EICR. Upgrading the bonding is pretty much impossible without massive disruption and taking part of the kitchen out. The CU is in the middle of the main house pretty much which is not small. Disappointed

    Real world issues trying to make things safer and I might walk away from upgrading it. 

    Gary

  • 0
    mapj1 said:
    Its not dangerous, but it may well not meet the letter of current regs.

    If it's PME, then diverted neutral currents is a possibility. The current is what it is, but with this arrangement, we can end up with voltages developing, so bonding in both places is really necessary ... DNO will be worrying about the bonding size back to the PME earthing terminal to help prevent overheating and control voltages ... I might not go as far as "not dangerous" if it is PME, although the danger will come from outside the installation, for example in the form of a broken PEN conductor.

  • 0 in reply to gkenyon

    My point is that  the gas pipe is the better conductor linking the two locations, by far.  Adding the still relatively high resistance of some 10mm or 16mm2 does not greatly reduce the fraction of the diverted neutral current in the gas pipe from the existing set up where the weedy parallel path includes the CPC of some 2,5mm, nor does it much alter the voltage drop across it or the 2.,5mm cpc.

    Mike.

  • 0 in reply to gkenyon
    gkenyon said:
    The bonding in both buildings is necessary to conform to BS 7671.

    I stand corrected (again Anguished ).

    mapj1 said:
    My point is that  the gas pipe is the better conductor linking the two locations, by far.

    That was my thinking.

    aligarjon said:
    Upgrading the bonding is pretty much impossible without massive disruption and taking part of the kitchen out.

    Can the bonding not take another route? With the garage electrical supply?

    TT the garage?

    Of course, if the two buildings were joined so that they became one, the electrical problem would vanish.

    (I have no idea whether it is permissible to use a bit of ordinary copper pipe underground to supply gas.)

  • 0 in reply to mapj1

    Agreed in one sense ... in another the additional bonding and remote location increases the chances that diverted neutral currents can lead to dangerous potentials in that installation ... especially if the pipe doesn't make contact with the mass of the earth between the garage and shed (possible if it's in a plastic outer).

  • 0 in reply to gkenyon
    gkenyon said:
    especially if the pipe doesn't make contact with the mass of the earth between the garage and shed (possible if it's in a plastic outer)

    I'll bet my bottom dollar that that pipe is not dry (most of the year).

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