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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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 18 April 2013 09:30 PM
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leckie

Posts: 1975
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When I posted the op I didn't realise that the Paul cook article was that old, I thought it was from his book, it was something I just googled.

Why I posted this question is that when carrying out an EICR, previously I would have coded missing main bonding for water and/or gas services even if the incoming supply was in plastic. You have to be very careful criticising, coding or even commenting on a EICR because if you are wrong it might come back and bite you! You are giving advice, so it better be right or at least sensible.

I do understand the argument for not bonding when there is a plastic incoming supply. However, I have been trying to more fully reason that argument because I know that if I fail to comment on missing bonding, and further down the line there is a subsequent EICR by others they may comment and code. I want to make sure that I can justify whatever stance I take.

Anyone want to buy a load of 10mm g/y cable? Looks like we don't need it anymore
 19 April 2013 09:13 AM
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OMS

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It's not difficult.

Regulation 411.3.1.2 sets out the requirements. It specifically requires bonding of extraneous conductive parts and gives a list of typical items that require bonding - but only if they are extraneous

And therein lies the problem - either the designer can determine if a service is extraneous and bond or he can predict if it may become extraneous and again, bond.

If the designer is certain the service isn't extraneous then he doesn't need to bond it.

Given that for "small" installations, the "designer" is usually the electrician doing the install, and that even within the domestic sector there are all sorts of variations of gas and water pipework, including re entrant sections etc and there is broadly no control of systems anyway, the "industry" has generally accepted that for avoidance of doubt (or avoidance of thinking by a competent person in reality) then regardless of the conductive or insulating nature of the service, if the internal pipework is conductive, then we bond it without question - it's the comparatively least risky option - better to bond what isn't actually extraneous rather than not bond what is potentially extraneous.

Of course, attitudes are shifting, DNO's are broadly washing thier hands of all responsibility for earthing systems, suppliers are increasingly using non conductive distribution and becoming ever more risk averse as to where they site the meters - so much so, that the industry now has to totally reconsider what it uses for guidance - the regulations are clear - it's the guidance that differs - often wildly, and generally reflects the age and experience of the author and the intended target readership.

Guidance that says "just do it" is basically trying to avoid the cost of thinking about it by creating a simple rule - which in reality is what installers want to hear ie "We always do it this way"

regards

OMS

-------------------------
Failure is always an option
 19 April 2013 10:11 AM
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rogersmith7671

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"In each installation main protective bonding conductors complying with Chapter 54 shall connect to the main earthing terminal extraneous-conductive-parts including the following:"
If you where to read further you would find "(ii) gas installation pipes", in a list of "conductive" parts that are included in the defined category of Extraneous- conductive-parts.
It's clear that 411.3.1.1 refers to parts that are not forming an actual part of the electrical installation, but are "conductive" and liable to present a potential, generaly that of Earth, which might give rise to danger. However the parts referred to must be "conductive".

Regards

Source: BS:7671, 411.3.1.2 Et al.
 19 April 2013 10:32 AM
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Parsley

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Originally posted by: rogersmith7671

"In each installation main protective bonding conductors complying with Chapter 54 shall connect to the main earthing terminal extraneous-conductive-parts including the following:"

If you where to read further you would find "(ii) gas installation pipes", in a list of "conductive" parts that are included in the defined category of Extraneous- conductive-parts.

It's clear that 411.3.1.1 refers to parts that are not forming an actual part of the electrical installation, but are "conductive" and liable to present a potential, generaly that of Earth, which might give rise to danger. However the parts referred to must be "conductive".



Regards



Source: BS:7671, 411.3.1.2 Et al.


411.3.1.2 is a list of general items found in buildings that could be extraneous-conductive-parts depending on how the items are installed, it doesn't mean they must be bonded without consideration.

Regards
 19 April 2013 11:39 AM
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rogersmith7671

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No, i think the operative word here is "shall", and not least, "conductive".
Have another read.

Regards
 19 April 2013 11:42 AM
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AJJewsbury

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No, i think the operative word here is "shall", and not least, "conductive".
Have another read.

It needs to be read in conjunction with the definition of an exposed-conductive-part on page 28.
- Andy.
 19 April 2013 11:44 AM
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Avatar for OMS.
OMS

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Originally posted by: rogersmith7671

No, i think the operative word here is "shall", and not least, "conductive".

Have another read.

Regards




The operative word is shall only if the part is an extraneous-conductive- part

It's why we don't bond metallic services served by insulated incoming supplies - they may be conductive but they aren't extraneous - the word conductive being read strictly in accordance with the special meaning of extraneous-conductive-part - note the hyphens

Regards

OMS

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Failure is always an option
 19 April 2013 12:10 PM
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Parsley

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Originally posted by: rogersmith7671

No, i think the operative word here is "shall", and not least, "conductive".

Have another read.



Regards


Carry on then if you're content not understanding why you might or might not need to install it.

Regards
 19 April 2013 12:15 PM
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rogersmith7671

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Quote:
It needs to be read in conjunction with the definition of an exposed-conductive-part on page 28.
- Andy.

yes, i did and that's Here;
It's clear that 411.3.1.1 refers to parts that are not forming an actual part of the electrical installation, but are "conductive" and liable to present a potential, generally that of Earth, which might give rise to danger. However the parts referred to must be "conductive".
This paraphrase was intended to define the conductive principle.

Quote:
It's why we don't bond metallic services served by insulated incoming supplies. Yes, it's the point i was trying to make
- they may be conductive but they aren't extraneous The O/P refers to a gas service pipe, which i am sure is extraneous, by definition.
- the word conductive being read strictly in accordance with the special meaning of extraneous-conductive-part - note the hyphens.
However you cut it, i think conductive means electrically conductive rather than heat, light, or any other sort of hyphenated radiation.


Regards
 19 April 2013 12:23 PM
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rogersmith7671

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Originally posted by: Parsley

Originally posted by: rogersmith7671



"In each installation main protective bonding conductors complying with Chapter 54 shall connect to the main earthing terminal extraneous-conductive-parts including the following:"



If you where to read further you would find "(ii) gas installation pipes", in a list of "conductive" parts that are included in the defined category of Extraneous- conductive-parts.



It's clear that 411.3.1.1 refers to parts that are not forming an actual part of the electrical installation, but are "conductive" and liable to present a potential, generaly that of Earth, which might give rise to danger. However the parts referred to must be "conductive".







Regards







Source: BS:7671, 411.3.1.2 Et al.




411.3.1.2 is a list of general items found in buildings that could be extraneous-conductive-parts depending on how the items are installed, it doesn't mean they must be bonded without consideration.

Exactly the point i'm trying to make, However the parts referred to must be "conductive", if say, they are, then the wording is they "shall" be bonded. sorry for any confusion


Regards
 19 April 2013 12:35 PM
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Avatar for OMS.
OMS

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Originally posted by: rogersmith7671

Quote:

It needs to be read in conjunction with the definition of an exposed-conductive-part on page 28.

- Andy.

yes, i did and that's Here;

It's clear that 411.3.1.1 refers to parts that are not forming an actual part of the electrical installation, but are "conductive" and liable to present a potential, generally that of Earth, which might give rise to danger. However the parts referred to must be "conductive".

This paraphrase was intended to define the conductive principle.

Quote:

It's why we don't bond metallic services served by insulated incoming supplies. Yes, it's the point i was trying to make

- they may be conductive but they aren't extraneous The O/P refers to a gas service pipe, which i am sure is extraneous, by definition.

How so - it nees to be able to introduce a potential - it can't do that if it's plastic for example

- the word conductive being read strictly in accordance with the special meaning of extraneous-conductive-part - note the hyphens.

However you cut it, i think conductive means electrically conductive rather than heat, light, or any other sort of hyphenated radiation.


I didn't suggest that - just the collection of words "Extraneous-Conductive-Part" have a specific meaning in BS 7671 - ie they need to be conductive, able to introduce a potential (and usually, accessible).

So two examples - a compressor supply line, in steel pipe that emanates from an internally mounted compressor - clearly conductive but not extraneous - so no bond.

Move the comressor outside the equipotential zone and the same system probably becomes extraneous - so bonded

A plastic gas main serving a metallic pipework installation within the equipotential zone - so conductive, but not extraneous - so no bond.


Regards


In my opinion the word "shall" is only relevant when the part is an extraneous conductive part - ie conductive and able to introduce a potetial - so both not either

Regards

OMS

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Failure is always an option
 19 April 2013 12:42 PM
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AJJewsbury

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yes, i did and that's Here;

Agreed - it was the next bit that threw me -
"(ii) gas installation pipes", in a list of "conductive" parts that are included in the defined category of Extraneous- conductive-parts.

you seemed to be saying that 411.3.1.1 defined that a conductive gas pipe was an exposed-conductive-part!

I think we've been mis-reading each other to our own detriment!

- Andy.
 19 April 2013 12:56 PM
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rogersmith7671

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Originally posted by: AJJewsbury

yes, i did and that's Here;


Agreed - it was the next bit that threw me -

"(ii) gas installation pipes", in a list of "conductive" parts that are included in the defined category of Extraneous- conductive-parts.


you seemed to be saying that 411.3.1.1 defined that a conductive gas pipe was an exposed-conductive-part!



I think we've been mis-reading each other to our own detriment!



- Andy.


Yes, Andy sorry for any unnecessary confusion.

Regards
 19 April 2013 01:03 PM
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AJJewsbury

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No worries! We got there in the end.
- Andy.
 19 April 2013 03:06 PM
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geoffsd

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Originally posted by: OMS
Given that for "small" installations, the "designer" is usually the electrician doing the install, and that even within the domestic sector there are all sorts of variations of gas and water pipework, including re entrant sections etc and there is broadly no control of systems anyway, the "industry" has generally accepted that for avoidance of doubt (or avoidance of thinking by a competent person in reality) then regardless of the conductive or insulating nature of the service, if the internal pipework is conductive, then we bond it without question - it's the comparatively least risky option - better to bond what isn't actually extraneous rather than not bond what is potentially extraneous.OMS


Excellent post and most helpful but I would like to point out, for those who are not sure, that the above applies to main bonding to incoming services when it is difficult to determine whether they are extraneous because of interconnections.

It does not apply to supplementary bonding where the need, or not, for supplementary bonding can be determined satisfactorily.

My point is that - to bond parts in a bathroom etc. which do not require bonding because we are not sure is not satisfactory.
The need for supplementary bonding of, say, a metal bath or radiator must be determined and not applied 'just in case' (because we are not sure) thinking it is the safer option.
It is not the safer option and, if not required, will introduce a danger which was not there before.
 19 April 2013 03:10 PM
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Parsley

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I don't think the bath or radiator would need bonding, the pipes serving them might though.

Regards
 19 April 2013 03:43 PM
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OMS

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Does it actually introduce a danger - if we take a section 701 supplementary bonding approach and end up bonding a non extraneous bath or radiator by mistake what danger does it bring.

It may rise in potential whereas before it wouldn't but given that we have captured all of the circuit CPC's and all of the real extraneous parts anyway we still have a zone of reduced touch potential.

regards

OMS

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Failure is always an option
 19 April 2013 03:56 PM
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AJJewsbury

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Does it actually introduce a danger - if we take a section 701 supplementary bonding approach and end up bonding a non extraneous bath or radiator by mistake what danger does it bring.

It looses the safety advantage of an insulating environment - 230V on one hand is fine if the other isn't earthed (bird on a bare overhead wire scenario). Earth the other hand (or foot) and the result is quite different. How low a voltage difference is guaranteed by supplementary bonding?
OK, insulating environments is not something we'd want to entirely rely on (unlike old continental practice in dry areas), but it seems daft to go to effort to throw it away if it's already there for free. Especially if the alternative is to rely on mechanical disconnection devices like RCDs.
- Andy.
 19 April 2013 04:02 PM
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geoffsd

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Yes, a wrongly applied bond is not a bond but an earth.



Originally posted by: ParsleyI don't think the bath or radiator would need bonding, the pipes serving them might though.

Geographically true, electrically false.
 19 April 2013 05:03 PM
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Avatar for OMS.
OMS

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Originally posted by: AJJewsbury

Does it actually introduce a danger - if we take a section 701 supplementary bonding approach and end up bonding a non extraneous bath or radiator by mistake what danger does it bring.


It looses the safety advantage of an insulating environment - 230V on one hand is fine if the other isn't earthed (bird on a bare overhead wire scenario). Earth the other hand (or foot) and the result is quite different.

But that's a direct contact shock Andy - the installation has already failed.

How low a voltage difference is guaranteed by supplementary bonding?

Pretty low actually if it's local supplementary bonding within a bathroom - R2 even over domestic distances is now much lower for no significant increase in fault current.

OK, insulating environments is not something we'd want to entirely rely on (unlike old continental practice in dry areas), but it seems daft to go to effort to throw it away if it's already there for free.

I'd be very hesitant about calling any bathroom an insulating environment - and I'm not sure we are throwing away much actually

Especially if the alternative is to rely on mechanical disconnection devices like RCDs.

But the much reduced touch voltage is there by default regardless of the disconnection device used - if we bring it down to less than 50V we don't need to disconnect at all

- Andy.


I'm not saying we should do it - we were initially talking about bonding a gas main - I just raised the point in response to the idea that supplementary bonding a bath or radiator may not actually result in an increased risk

regards

OMS

-------------------------
Failure is always an option
IET » Wiring and the regulations » Incoming gas services

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