mains gas pipe bonding,?

[joesoap1]

The more conductive the water pipe is, the more important it is that it is bonded. The danger presented by gas and water supplies is that they can introduce an earth potential to the building that is different to the earth potential of the electrical supply (at the MET). The main bonding minimises the potential difference between exposed and extraneous conductive parts in the installation during an earth fault.

Tony, you are right that main bonding of an incoming service is not required where the service pipe and pipework within the installation are both of plastic. However, quoting from the BS7671:2008 On-site guide: ‘Where there is a plastic incoming service and a metal installation within the premises, main bonding is recommended unless it has been confirmed that any metal pipework within the building is not introducing earth potential.

Hi Mikely, can you clarify for me why the bonding has to be within 600mm of gas meter and water inlet, yet all of the pipes terminate in my garage at the boiler 5 feet from MET.on the same wall.? Whats the reason for running 2 X 40 feet of bonding cable paralell to pipework to MET, when it all can be bonded at 1 point in garage and run 5 feet to MET.Appreciate your advice, it,s very helpful. Cheers

the requirement for a gas pipe to be bonded within 600mm of the meter outlet comes from BS6891 (pipework install BS) which says the first 600mm of pipe needs to be rigid pipe before it changes to trac pipe etc, and the requirement to bond onto to rigid pipe, therefore it makes sense to ask for the bonding to be within 600mm so that it will always be on the rigid pipe, ask any spark where the bonding needs to be and he will tell you anywhere as long as the ze reading is correct, remember before we cut a pipe we should be using a temp continuity bond, so we should be protected wherever the spark has put the connection, (i think the sparks regs require the bond to be fitted within the equipotential zone where accessible) which with an outside meter and chipboard flooring could be 6m inside the prop beside the boiler

Hi, Thanks for reply.As my gas run from the meter to boiler is approx 16 metres, all rigid, with one tee to gas fire, approx 1200mm from meter, the bond has to be before the tee.according to regs.Also I shall bond to water, on the way, continuous, so I reckon on 20 metres of cable.The tee would eliminate bonding closer to the boiler on gas pipe,direct to MET, I presume.? I will bond to as many water tees as possible on route to MET also.Cheers

 

[Agile]

Those setting the regulations take account of the fact that any non soldered joint may NOT be a good electrical conductor.

Many pipes are being joined by fittings like Tectite which will not necessarily provide electrical conductivity.

The reason a thick 10 mm cable is chosen is that it has to be guaranteed to be able to blow a 100A incoming mains fuse. If a fault blew an earth connection then it would be possible for a gas pipe for example becoming live at mains voltage.

Tony

 

[Ray84]

id wondered why it had to be 10mm, i feel like a jobs worth marking down when it has bonding but undersized but makes sense now
cheers Tony

 

[joesoap1]

Those setting the regulations take account of the fact that any non soldered joint may NOT be a good electrical conductor.

Many pipes are being joined by fittings like Tectite which will not necessarily provide electrical conductivity.

The reason a thick 10 mm cable is chosen is that it has to be guaranteed to be able to blow a 100A incoming mains fuse. If a fault blew an earth connection then it would be possible for a gas pipe for example becoming live at mains voltage.

Tony

Cheers Tony, my mate, ex sparky, retired 3 years ago has just called to look at my job. He said the 600mm rule was "probably" to do with joints and conductivity.6mm was what he last used, and would have normally bonded all at boiler point.Shows how regs changeso quick.Just going to cost me arm and a leg for 10mm2 cable @ Approx £2 per metre.Got to be done.

 

[5544]

i think there is some confusion here.
if you are talking about main equipotential bonding then yes it is 10mm cable, and the reason why it seems to always increases in size is due to a number of factors such as loadings on new installations and disconnection times of safety devices.. now if you are talking about providing this bonding as part of the boiler installation then yes you should use 10mm cable. if however the house has already got main equipotential bonding to all services then you only need to provide supplementary bonding at the boiler which is 4mm earthing cable.

to make things more confusing, if your house complies fully with the 17th edition regs then you do not need to do the latter.

 

[joesoap1]

i think there is some confusion here.
if you are talking about main equipotential bonding then yes it is 10mm cable, and the reason why it seems to always increases in size is due to a number of factors such as loadings on new installations and disconnection times of safety devices.. now if you are talking about providing this bonding as part of the boiler installation then yes you should use 10mm cable. if however the house has already got main equipotential bonding to all services then you only need to provide supplementary bonding at the boiler which is 4mm earthing cable.

to make things more confusing, if your house complies fully with the 17th edition regs then you do not need to do the latter.

Hi, Thanks, more confusion.As OP, my boiler has been in 16 years approx, installed by previous owner, who was/is a sparky.I automatically assumed it complied with regs, would that be 16th?1995.However, this week, boiler contract people, Homeserve came to repair it. During the repair, they did inspection and picked up on 5 faults, one being, they could not see gas pipe bonding at the gas meter.they gave me at risk notice, I assumed it must be under floor, easily accessable through hatch, 3 feet deep and narrowing to 1 foot at garage end where boiler is, and CB.On my inspection, I could not see any bonding on gas pipe or water, so assumed it must be elsewhere.or not at all.That,s the status quo, do I assume it,s not bonded somewhere I cannot see and do it to MET,which there is not one at present.using 10mm2 ?or assume it,s bonded elswhere, spiked, and bond it at boiler using 6mm2? to new MET

 

[mikely]

What the main bonding is doing is 'intercepting' an external earth potential that may be introduced into the building via a gas or water pipe. It thus has to be connected as close as practicable to the point of entry. As has been pointed out, connections along the pipework may interrupt the electrical continuity. Thus if you were to bond at the boiler and the electrical continuity was interrupted just before the boiler, the 40 feet of pipework going all the way back to the meter would still be at the external earth potential during a fault condition. The bonding is then not doing its job.

 

[joesoap1]

What the main bonding is doing is 'intercepting' an external earth potential that may be introduced into the building via a gas or water pipe. It thus has to be connected as close as practicable to the point of entry. As has been pointed out, connections along the pipework may interrupt the electrical continuity. Thus if you were to bond at the boiler and the electrical continuity was interrupted just before the boiler, the 40 feet of pipework going all the way back to the meter would still be at the external earth potential during a fault condition. The bonding is then not doing its job.

Thanks mikely, that clarifies it. The job will be done using 10mm2, and 600mm from both gas meter and water inlet pipe.to new MET on board. Cheers

 

[bengasman]

Water pipes no longer need to be bonded as most have plastic sections so cannot be relied on to be good earth....

New to me Tony. Last I heard was missing meb on either gas or water is a code 1 fail.

It is not a matter of relying on the earth of a pipe, it's a matter of making sure no extraneous conductor can become live.

 

[bengasman]

...supplementary bonding at the boiler which is 4mm earthing cable.

That was 2.5 actually unless it is unprotected under 16th edition

 

[bengasman]

What the main bonding is doing is 'intercepting' an external earth potential that may be introduced into the building via a gas or water pipe..

No, it does not.
It prevents metal parts from becoming live under fault conditions.

 

[joesoap1]

What the main bonding is doing is 'intercepting' an external earth potential that may be introduced into the building via a gas or water pipe..

No, it does not.
It prevents metal parts from becoming live under fault conditions.

Hi,As I have to do it, it has to be right.One question if I may.AS I have to bond within 600mm of gas meter, then run the 10mm2 cable approx 15 metres to the MET, just measured it, under the floor, which is accessable, scrawling,the actual bonding clip is not visible to whoever wants to check it,as this has occurred and me being at the status quo.WOULD I be better off continuing cable through the outside wall alongside the gas pipe, using same trunking and bond it within the meter box, where it,s visible?

 

[JohnD]

These can either be run separately or via one unbroken cable linking both to the MET.

I had a look at the article which says "the conductor should be continuous"
(this suggests guidance - if there is a regulation it would say "must")

This question has cropped up before - can you find a regulation that says it must be a single unbroken cable?

 

[bengasman]

...AS I have to bond within 600mm of gas meter, then run the 10mm2 cable approx 15 metres to the MET, just measured it, under the floor, which is accessable, scrawling,the actual bonding clip is not visible to whoever wants to check it...

All screwed electrical connections must be accessible for inspection. Whatever way is easiest for you, is the way to go.
If you don't want to connect outside, you can connect inside as close to the meter as is reasonably possible, even if that is more than 600 mm from the meter.
Bear in mind that the inspector will have to put his tester on the clip, so best not to go overboard with the location. Also, the connection must be very clean as the total impedance of the whole meb must be less than 0.05 Ohm.

 

[londonboy]

Some good advice from Bengasman, however some of the rest is incorrect and misleading.

This should be in electrics forum.