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gas installation pipe bonding [again]

psychicwarrior
"My head is in a spin, my feet dont touch the ground..."  - I think I am just wanting to unload my head to the almighty interweb (at least it is not to that facebook thingy) and in that, it will heal. :)


A description: a gas meter is in its cupboard outside on the side of a house and the service pipe coming out of the ground to it, at this stage, I am assuming to be conductive (or not plastic). The bare copper installation pipe from the meter, comes out of the top of the cupboard, goes  up the wall and around the outside of the house (at a touchable height) to the opposite side, a run of about 12 metres, where it enters the building though the wall and attaches to the boiler.  I am told this is quite common.


As an aside, for now, the visiting gas engineer said to the property owners, that because of how it is run, he wanted to see some bonding connected inside the meter cupboard on the installation pipe side , not elsewhere, or it would get a notice. *


What I am curious about is the approach to running an accessible [and conductive] pipe aroung the outside of a house (rather than getting it inside immediately) and bonded to the MET when there could be a fault on the installation.  It must be in the similar vein as  a small 'class one' light fitting being installed on the wall outside, that this is seen as an allowable potential shock risk even when it would be accessible for such a distance as it were when 'lively' ?   Or am I over-thinking this, or just getting it all wrong (as is my wont) with a "there is no issue here actually".


Regards

Habs


* I am starting to dislike use of some partial plastic pipe alterations in properties.  Keeping it brief as this is just part of the 'aside' comments: there are plastic sections a little after the copper 'out/return' pipes on the boiler which disappear into the house structure to goodness knows where.  Something else, or the copper pipe still visible elsewhere servicing radiators and so forth, seems to be keeping those parts extraneous. With a lot of pipe 'buried', it is quite tricky to spot whats going on.   As it happens, there is a MEB cable clamped to a copper pipe feeding a radiator on an internal wall, which then runs through the wall to the  MET on the other side.  This would seem to be doing its job for all the extaneous parts (gas and water connected) when assessing with it connected/disconnected. The connection is not in the ideal position, open to risks of being disconnected from more [future] alterations but it is working and perhaps the previous sparks decided this was the best to be done in the circumstances.  Its a bonding conundrum to find a good solution - if only it were all plastic, or still all copper...ho hum.
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    This is a slightly tricky one because the gas and BS7671 are not in step. The gas people do not seem to understand that mains bonded pipes outside may represent a danger under certain fault conditions, and BS7671 only requires bonding if the pipes can introduce an external potential into the property. However the idea that the bonding right by the meter is probably incorrect and 544.1.2 states they should be connected at the point of entry to the property. If there is a plastic service then bonding is not required at all, although plumbers appear to be unaware of this, probably because they have been bombarded by "main and cross bonding" for many years! In my view the risk of the pipe is very small and bonding it is probably unavoidable anyway because of the boiler earthing system. So to avoid silly regulatory arguments one may as well do as the gas man wants, although they do love to wield "immediate danger" notices, particularly BG!
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    It must be in the similar vein as  a small 'class one' light fitting being installed on the wall outside, that this is seen as an allowable potential shock risk even when it would be accessible for such a distance as it were when 'lively' ? 



    Agreed - or the other usual example - the outside tap.


    That's the big flaw with the equipotential zone theory - it can't, by definition, work across the boundaries of the zone. Making the edges of the zone inaccessible or a wide 'insulating' area helps, but the basic problem remains (especially where extension leads may be used).

     

    As an aside, for now, the visiting gas engineer said to the property owners, that because of how it is run, he wanted to see some bonding connected inside the meter cupboard on the installation pipe side , not elsewhere, or it would get a notice. *



    Well I'd like to see it kept out of the meter box if at all possible (and I suspect the gas regs have similar reservations - as I recall drilling a hole through back of the meter box (e.g. to run the G/Y through) is forbidden). At the point of entry would do nicely. If he wants to argue bonding with BS 7671 then my money's on the blue book. My only concession to such situations is to leave a label in the meter box stating something to the effect that the main bonding is present and located inside at the point of entry, in compliance with BS 7671.


       - Andy.
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    Out of interest I just had a look at the earth bonding here in Kelly towers the gas is bonded where the copper pipe feeding the hob and boiler comes out the floor  this is a good 30 feet from the meter but only a few feet from the MET. In the bathroom the radiator is bonded to the plumbing under the bath and then into the earth terminal in the shower pull switch. This was all done by the then SEB when we had a new consumer unit fitted  we are on a standard supply ie not PME. If the SEB can do it that way then surely it's ok for the rest of us
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    the gas is bonded where the copper pipe feeding the hob and boiler comes out the floor



    If that's the first place where the gas pipe enters the habitable area (e.g. the meter is outside) then that's the ideal location for the bond.


     

    we are on a standard supply ie not PME



    'Standard' DNO's earthing facility these days should be regarded as being PME - since DNOs tend to combine N and PE during repair and maintenance work. Having an old "TN-S style" head or the lack of a PME sticker is no guarantee at all. Unless it's TT or you've got a written statement from the DNO (unlikely except possibly for a marina or caravan park) - then good practice is to treat as PME.


     

    I am starting to dislike use of some partial plastic pipe alterations in properties.



    Provided things are correctly bonded at 'point of entry' (which might be better thought of as point of entry of a potential that makes the part extraneous, rather than entry of the gas.fluid inside the pipe)  - then insulating section aren't an issue. If a pipe is separated from the bonding by an insulating section then it's also separated from the thing than requires it to be bonded in the first place - so it all comes out in the wash.


       - Andy.
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    Hi AJ The gas pipe is under a wooden floor all the way from the front of the property to the point where it finally emerges it would of been impractical to fit the bond any closer than where it I as this would of meant lifting floorboards and lifting a big old carpet. Oh and disturbing the mice as well. I had temporarily forgotten that DNOs tend to link N and E these days call it a  memory fade!
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    ...Provided things are correctly bonded at 'point of entry' (which might be better thought of as point of entry of a potential that makes the part extraneous, rather than entry of the gas.fluid inside the pipe)  - then insulating section aren't an issue. If a pipe is separated from the bonding by an insulating section then it's also separated from the thing than requires it to be bonded in the first place - so it all comes out in the wash.


       - Andy.

     




    The part that gets separated from the bonding by a plastic insert could, by going into, though or in contact with earth under the floor, still be extraneous part in the zone ?  What to do if that (as rare as it may be) happens - bond those sections as it appears to have happened from some previous works (MEB from rad pipe to MET I mentioned).


    I can see the plastic inserted sections (and some flexi pipe !), a few metres after internal pipes leave the boiler (not the gas supply coming into the boiler from outside that I mentioned), as they disappear into a void through a wall and under the floors (cant inspect from there on as the under floor voids are inaccessible in that area). There is no plastic re-appearing at rads, sinks etc, it is copper rising and it is presenting as extraneous still, so somewhere something else is going on and might explain why previously a MEB was added at that rad pipe.  I know it is not at entry point, but if that entry point


    I am going to go back and have another poke around and recheck to get a 'better' understanding. I'm wondering if I've mistaken or not spotted another entry point or something; possible !


    It all would help if folks left records when [significant] alterations take place.  :)



    Thanks all, for the responses.

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    Aren't all internal gas pipes required to be metal and not plastic?


    Z.
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    The part that gets separated from the bonding by a plastic insert could, by going into, though or in contact with earth under the floor, still be extraneous part in the zone ?



    That's why I (tried) to make the point about the point of entry of potential, rather than the point of entry of the gas (or water, or oil or whatever). If you had a water supply coming out of the ground in plastic, internal copper pipework but then the copper going underground (say to serve a tap at the bottom of the garden, or an outbuilding), the the ideal point for a main bond for the water would be where it goes out, back underground, rather than at the stop cock. If the supply was metallic and the branch to the garden metallic as well, ideally you'd bond at both positions.


       - Andy.
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    Aren't all internal gas pipes required to be metal and not plastic?



    Yes, but there can be insulating joints - sometimes specified at gas meters (internal or external) specifically to reduce the chances of currents flowing through the gas pipework. Hence the otherwise rather odd requirement to bond to the consumer's pipework (after the meter) rather than the service pipe before the meter.


       - Andy.
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    AJJewsbury:


    That's why I (tried) to make the point about the point of entry of potential, rather than the point of entry of the gas (or water, or oil or whatever). ...


       - Andy.

     




    Didn't pick that up.  Sorry.  Understood.

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