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Topic Title: Incoming gas services
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Created On: 17 April 2013 09:20 PM
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 17 April 2013 09:20 PM
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leckie

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Hi all

Been reding lots bout incoming plastic water services with reference to bonding. What about gas? Are the yellow pipes plastic in new installations?
 17 April 2013 10:38 PM
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DOUGIE1000

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Gas regulations gas installs have to be copper for mechanical and rod ant protection.

The supply pre meter is common the be plastic or MI.

Bonding still as normal.

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 17 April 2013 10:45 PM
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daveparry1

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So if water doesn't need bonding if the supply enters in plastic, why does gas? Just a thought! (I usually bond the internal pipework anyway even if the supply is in plastic, both water and gas)

Dave.
 18 April 2013 07:51 AM
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UKPN

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"I usually bond anyway"

of course, and its correct, but you try telling that to our esteemed consultants!

Regards, and have a good day!
 18 April 2013 08:14 AM
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leckie

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So is there a difference between the requirements for bonding water with incoming plastic service and water with plastic incoming service? Is there for instance a specific gas regulation ?

This is an extract from Paul Cook and looks like pre 17th BS7671. It refers to bonding required for metal pipe installation even if incoming service is plastic, and makes no distinction between water or gas. He also distinguishes between water supplies and central heating systems. So even if there is an argument for not bonding water pipes with a plastic service, is there still a requirement if there is a central hearing system with some copper pipes?

http://www.plasticpipesgroup.com/pdfs/earthbonding.pdf
 18 April 2013 08:26 AM
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ebee

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It boils down to (forget the pun) "is the metal pipework extraneous" (likely to introduce a potential - Earth is a potential and is usually the one we are looking at for this purpose).

If it`s not then no need to bond.
However if you consider it is likely to become so then you might decide to bond anyway but you should bear in mind that bonding would introduce a potential to pipework that did not require bonding in the first place because it had no potential until you bonded it. Which now makes it potentially less safe than if it was not bonded.

-------------------------
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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 18 April 2013 08:46 AM
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leckie

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I know that is what is said Ebee, but that does not appear to be what the highly respected Paul Cook is saying. Many of the top brains on this forum have highly praised his book as being a definitive read on electrical installation but he appears to say if it is a metal or part metal installation, regardless of the service pipe material, main bond it.

The ESC say that if it can be proven that the pipes are no an extraneous conductive part then no requirement.

So that's two "authorities" who don't appear to agree.
 18 April 2013 09:31 AM
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AJJewsbury

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I know that is what is said Ebee, but that does not appear to be what the highly respected Paul Cook is saying. Many of the top brains on this forum have highly praised his book as being a definitive read on electrical installation but he appears to say if it is a metal or part metal installation, regardless of the service pipe material, main bond it.

The ESC say that if it can be proven that the pipes are no an extraneous conductive part then no requirement.

So that's two "authorities" who don't appear to agree.

I think there's been a gradual change of emphasis over time. Earth potential can be introduced from a number of directions - it's not dependent on the the direction of flow of the water or gas for instance - so isn't exclusively an issue for incoming service pipes. You could have a incoming plastic water pipe but the 'consumer side' copper pipework could sill be extraneous if there was a connection to true earth elsewhere - e.g. going back underground to a garden tap, buried under a concrete floor or even plastered into a damp masonry wall. So it can be difficult to establish (especially at first fix stage when plumbing might not be complete) whether pipework will be extraneous- or not, and even more difficult to ensure that any future plumbing alterations (in old days almost always in metal), might change things over time, so the general policy of 'if in doubt bond' was sensible.

Nowadays, it's almost inconceivable that someone would run an underground supply to a garden tap in anything other than MDPE and decent test meters are pretty much universal, so a more pragmatic approach is taking over. Paul Cook's paper you link to appeared in Wiring Matters I think the best part of a decade ago and was I suspect aimed at the problems of the day - i.e. people literally putting clamps on plastic pipes or having short copper inserts placed in plastic systems to have something to bond to. I think there's also a greater appreciation that main bonding can sometimes be of quite limited benefit, especially for internal faults on TN systems. The latest GN8 is probably a better reference for current 'authoritative' thinking.

- Andy.
 18 April 2013 09:52 AM
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Parsley

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Try working out the likely touch voltage with and without bonding in TN systems, The benefits of bonding on TT systems are much greater.

Regards
 18 April 2013 09:54 AM
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ebee

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A lot of the houses I rewire are circa 1900 stone teraced with metal pipework so even if the incomer was plastic a lot of the old pipework is extraneous , however if it`s been replumbed in recent on the gas and water side then it might not need bonding. if it`s not replumbed then it probably is best to bond it.

I think modern buildings might err towards no bonding required

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 18 April 2013 12:55 PM
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geoffsd

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Why does 544.1.2 require main bonding after an insulating section regardless and how does this differ from an insulating section which may be the supply pipe?
 18 April 2013 01:07 PM
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AJJewsbury

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Why does 544.1.2 require main bonding after an insulating section regardless

I don't read it as requiring bonding regardless - just that if you are bonding (a decision governed by 411.3.1.2) and there is an insulating insert at the point you'd normally want to connect the bond, then that's how to do it.

If the consumer's pipework is still extraneous (i.e. is introducing a (earth) potential) even when the supply pipe is plastic, then the earthiness must be on the consumer's side of the insulating section - so in that circumstance it makes sense to bond on the consumer's side.

- Andy.
 18 April 2013 01:13 PM
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Parsley

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Originally posted by: geoffsd

Why does 544.1.2 require main bonding after an insulating section regardless and how does this differ from an insulating section which may be the supply pipe?


The protective bonding is trying to keep the consumer's pipework at the same potential as the MET. If there is an insulating section on the incoming section then the consumers pipework after it might not be an extraneous-conductive-part and bonding might not actually be doing anything, but you should consider what is flowing through the pipe as well and whether that could introduce a potential.

Regards
 18 April 2013 04:19 PM
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geoffsd

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Yes, I understand the purpose of bonding but an insulating section will remove the pipe's 'extraneousness' so, if AJJ's reading is the correct one, why is 544.1.2 there at all.

If the pipe is still extraneous because of connections (with true earth) elsewhere then surely it should be bonded at the source of the extraneousness and not at the insulating section.
 18 April 2013 04:26 PM
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Parsley

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Originally posted by: geoffsd

Yes, I understand the purpose of bonding but an insulating section will remove the pipe's 'extraneousness' so, if AJJ's reading is the correct one, why is 544.1.2 there at all.



If the pipe is still extraneous because of connections (with true earth) elsewhere then surely it should be bonded at the source of the extraneousness and not at the insulating section.


If the pipework goes back into the ground under the DPM and re-appers it should also be bonded where it re-appears.

Regards
 18 April 2013 04:27 PM
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OMS

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Originally posted by: UKPN

"I usually bond anyway"

of course, and its correct, but you try telling that to our esteemed consultants!

Regards, and have a good day!


LoL - Correct ? - explain to me why, again - and remember that your so called regulation is for the adherance of fools and the guidance of wiser men -

Regards

OMS

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Failure is always an option
 18 April 2013 04:32 PM
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AJJewsbury

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If the pipe is still extraneous because of connections (with true earth) elsewhere then surely it should be bonded at the source of the extraneousness and not at the insulating section.

I agree - although for water pipes a short insulating section might not be completely successful in removing the "extraneousness" (I think we concluded a while back that around 200mm might be necessary - depending on pipe diameter and water conductivity). I've yet to see any guidance that explicitly deals with plastic incomer, mixed copper and plastic internal plumbing and a buried copper pipe on the customer's side to a garden tap or outbuilding. It might come in time ....

- Andy.
 18 April 2013 04:36 PM
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geoffsd

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Thank you, all.
 18 April 2013 07:54 PM
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Martynduerden

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Bs6891 requires a gas supply to have a minimum of a 10mm bond, however more generally it requires compliance with bs7671, essentially this as I read it means if the pipe is extraneous then it must be bonded with 10mm, if its not extraneous it does not require a bond.

-------------------------
Regards

Martyn.

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www.electrical contractors uk.com
 18 April 2013 07:57 PM
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Martynduerden

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As for an insulating section, I thought that was referring to tn-c-s systems where exporting the bonded metalwork may cause a hazard.

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
IET » Wiring and the regulations » Incoming gas services

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