Gas meter not bonded, what diameter (4mm/6mm/10mm) GY earth wire should be used?

[EFLImpudence]

Is there not an inconsistency there? If (as I agree appears to be allowed by the regs) the water pipe can be used as the main bonding conductor for the gas supply (but not vice versa), why can't it also be used as the main bonding conductor for itself?

It depends what you mean by an inconsistency.

Obviously the water pipe alone cannot be its own bond because it is not connected to the MET.

As you know, the regulation calls for the bond to be at the point of entry where practicable (not where practical).
Aso, as you know and have stated before, the resistance of the pipe is far lower than the bonding conductor thus connection of the pipe, to the MET, could be done anywhere with the same result if confirmed.
I presume the at the point of entry requirement is because that is where the potential may be introduced and, if done elsewhere it may be disconnected by alteration or effectiveness reduced by resistive joints within the premises.

 

[JohnW2]

Is there not an inconsistency there? If (as I agree appears to be allowed by the regs) the water pipe can be used as the main bonding conductor for the gas supply (but not vice versa), why can't it also be used as the main bonding conductor for itself?

It depends what you mean by an inconsistency. ... Obviously the water pipe alone cannot be its own bond because it is not connected to the MET.

Sure, but I think you know what I meant ... if a (potentially long) length of water pipe were bonded to the MET close to the MET (i.e. a very short cable) then the remainder of the bonding conductor back to "the point of entry where practicable" could be the pipe itself, couldn't it? I don't think there is anything in the regs which says the bonding conductor has to be a G/Y cable, rather than some other acceptable form of 'bonding conductor', is there?

I presume the at the point of entry requirement is because that is where the potential may be introduced and, if done elsewhere it may be disconnected by alteration or effectiveness reduced by resistive joints within the premises.

Yes, probably - but you have suggested that the water pipe (the electrical continuity of which might conceivably be interfered with in the future) would be acceptable as a bonding conductor for the gas pipe, so why not also for the water pipe itself?

Kind Regards, John

 

[Adam_151]

The logic is sound, john, however its moot because use of a water pipe would fall fowl of 543.2.6 (iii) as you allude to yourself.

Structural steelwork, however is commonly bonded close to the mains room and is sometimes used as a bonding conductor to other services, removal of this generally has bigger implications for the building than loss of bonding continuity

Its often also used as an additional CPC... supplimently bonds between board and the steel work might be specified in order to lower the earth loop

 

[FiremanT]

All gas meters, unless I am seriously mistaken, are metal.

But can anyone explain Nat Grids logic here:
If they go to a job, and the bond is not there at all,work is completed, and a warning card left explaining the requirement.
If the bond is on the inlet, they abort the job until it is rectified. And the guys are not allowed to move it.

Also, is it just me that was mistaken about joins? Or will any fellow RGI's put their hands up

 

[JohnW2]

The logic is sound, john, however its moot because use of a water pipe would fall fowl of 543.2.6 (iii) as you allude to yourself.

Well, that reg is a bit vague, but since it's existence implies that it can be satisfied, one imagines that sufficiently frequent "do not remove" labels along the length of the pipe might suffice.

However, you may be missing the point. I am not advocating using a water pipe as a bonding conductor. However, EFLI suggested that it could be used as the bonding conductor for bonding the gas service, and I don't understand why, if he believes that, he seems to feel that it cannot be used as the bonding conductor (back to 'the point of entry') for the water pipe itself.

Kind Regards, John

 

[JohnW2]

All gas meters, unless I am seriously mistaken, are metal. ... If the bond is on the inlet, they abort the job until it is rectified.

It may well be true that they are all metal, but that does not guarantee a low enough electrical impedance between inlet and outlet pipes (particularly if any sealing compounds, PTFE tape or whatever were used - but it probably isn't). That being the case main bonding applied to pipework on the outlet side of the meter might not adequately serve the purpose of main equipotential bonding. In fact, in the rare case of an electrical supply-side fault which resulted in very high currents (potentially hundreds of amps) flowing through the bonding to the incoming gas supply pipe (which is the scenario which everyone worries about), it could presumably be catastrophic, since very high temperatures and/or (worse) sparks/arcing could be generated within the meter or its couplings by the high current. Even though there ought not to be any air/oxygen around, that idea does not make me feel comfortable - so I find these practices rather hard to understand!

Also, is it just me that was mistaken about joins? Or will any fellow RGI's put their hands up

For all I know, the 'gas world' may have other/different regulations. However, as you have been told, as far as the Wiring Regulations (BS7671) are concerned, joins in the bonding conductor to a gas pipe (or any other extraneous-conductive-part) are not disallowed.

Kind Regards, John

 

[flameport]

Gas meters are usually attached to metal brackets which also hold the incoming and outgoing pipes, so there is usually electrical continuity even if the meter is removed.

 

[EFLImpudence]

However, EFLI suggested that it could be used as the bonding conductor for bonding the gas service, and I don't understand why, if he believes that, he seems to feel that it cannot be used as the bonding conductor (back to 'the point of entry') for the water pipe itself.

I don't think I said that.
I did say it couldn't actually be its own bond because it is not connected to the MET so you have to have a bonding conductor somewhere from MET to pipe.

If the water pipe travelled below the MET then a very short conductor would bond it and the resistance between the MET and point of entry may very well be negligible. (as I said - confirmed).
I also said I believe the regulation calls for point of entry to negate any subsequent alterations to the pipework.
If that is the reason - the regulations being concerned more with alteration than bonding conductor position itself - then it should be done at the point of entry

 

[JohnW2]

Gas meters are usually attached to metal brackets which also hold the incoming and outgoing pipes, so there is usually electrical continuity even if the meter is removed.

That may well usually be true (I have no idea) but (a) would you 'stake your life' on the fact that it was always going to be true? and, probably far more pertinent, why not just main bond the incoming gas supply on the inlet side of the meter, and hence do away with any uncertainty or safety concerns?

Kind Regards, John