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Topic Title: Main bonding and water services
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Created On: 31 March 2013 07:59 PM
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 31 March 2013 07:59 PM
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frspikeyhead

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Ok anything below 23k can be considered to be extraneous and needs bonding. Considering both metal gas pipes and water pipes are presumed connected at the boiler how would you measure whether an incoming water service pipe is extraneous without disconnecting either the gas pipe or water pipe.
 31 March 2013 08:11 PM
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daveparry1

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Forget about the 23k business, gas and water should be main bonded anyway, (unless the water supply comes in in plastic),

Dave.
 31 March 2013 08:17 PM
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sparkiemike

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Originally posted by: frspikeyhead

Ok anything below 23k can be considered to be extraneous and needs bonding. Considering both metal gas pipes and water pipes are presumed connected at the boiler how would you measure whether an incoming water service pipe is extraneous without disconnecting either the gas pipe or water pipe.



You can't, it is only feasible if you can be sure you have removed those other parallel paths (e.g. boiler, tank and CH controls), perhaps on a new build/installation.
 31 March 2013 08:18 PM
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frspikeyhead

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The premises in question has incoming plastic service mains, or so the householder claims, although I have come across plastic coated copper before. However, after the stop cock the water pipes once again go down into the concrete so I need to ascertain whether they need to be bonded which will be a **** of a job, hence the inquiry.
 31 March 2013 08:28 PM
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sparkiemike

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The onsite guide recommends where you have plastic incoming services and a metal installation in the premises that you bond the metal services unless you can confirm that the metal pipe work is NOT introducing earth potential. Without talking the installation apart it is not going to be easy to prove that.
 31 March 2013 08:28 PM
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daveparry1

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I have a similar one to do, water comes in in plastic then after the stop-cock goes back into the concrete to the opposite side of the house, combi boiler in the garage near to the gas meter and c/unit so water is going to be bonded in garage. (near as practicable!)

Dave.
 31 March 2013 08:46 PM
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davezawadi

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If you are worried just bond them at a convenient point, but this is not main bonding is it? I'm sure that you can tell a few ohms max from an extraneous figure, measured to the incoming neutral, so deciding whether either pipe can carry a significant current. Incoming services on newish build are very unlikely to be metal below ground.

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 31 March 2013 08:56 PM
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frspikeyhead

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There is no worries I am just trying to get out of bonding them as it wasn't in the original quote and they are not prepared to budge on the price. I didn't realize the pipe went back down into the concrete.
 31 March 2013 09:06 PM
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primo

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Originally posted by: davezawadi

I'm sure that you can tell a few ohms max from an extraneous figure, measured to the incoming neutral, so deciding whether either pipe can carry a significant current.


Could you please explain what you mean here?
 31 March 2013 09:10 PM
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weirdbeard

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Schrödinger's Conductive Parts.......?

Can there actually be such a thing as an extraneous conductive part in a a properly earthed and bonded installation or do extraneous conductive parts only exist on paper before an installation is installed? (not including installations that are not properly designed and/or installed)



If a conductive part (pipe) is metallicaly connected to earthed equipment (boiler) is it not an exposed conductive part?

If a conductive part (pipe) is not metallicaly connected to earthed equipment, and is said to be an extraneous conductive part, but is connected to the earthing system by a bonding conductor does it then cease to be an extraneous conductive part and become an exposed conductive part?

???
 31 March 2013 09:13 PM
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frspikeyhead

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Things start getting complicated when you have a mixture of plastic and copper within the installation.
 31 March 2013 09:22 PM
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daveparry1

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Far better to bond and be done with it I say, sometimes easier said than done but there's always a way. FR, you said bonding wasn't in the original quote, if this was an oversight by you just do it and put it down to experience!

Dave..
 31 March 2013 09:28 PM
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frspikeyhead

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There goes my profit margin again. Already done 3 charitable jobs, as I call them, this month..........
 02 April 2013 01:54 PM
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OMS

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Originally posted by: weirdbeard

Schrödinger's Conductive Parts.......?



Can there actually be such a thing as an extraneous conductive part in a a properly earthed and bonded installation or do extraneous conductive parts only exist on paper before an installation is installed? (not including installations that are not properly designed and/or installed)

Nope - they are real, they exist - in many forms.

If a conductive part (pipe) is metallicaly connected to earthed equipment (boiler) is it not an exposed conductive part?

Nope - read the definition - how can the pipe become an exposed part when it doesn't form part of the installation

If a conductive part (pipe) is not metallicaly connected to earthed equipment, and is said to be an extraneous conductive part, but is connected to the earthing system by a bonding conductor does it then cease to be an extraneous conductive part and become an exposed conductive part?

Nope - it's still an extraneous conductive part - read the definition - it doesn't form part of th eelectrical installation, it's not electrical equipment etc

???


Regards

OMS

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Failure is always an option
 02 April 2013 02:13 PM
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weirdbeard

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Originally posted by: OMS

Originally posted by: weirdbeard





Can there actually be such a thing as an extraneous conductive part in a a properly earthed and bonded installation or do extraneous conductive parts only exist on paper before an installation is installed? (not including installations that are not properly designed and/or installed)



Nope - they are real, they exist - in many forms.


Hi OMS, could you give examples?

If a conductive part (pipe) is metallicaly connected to earthed equipment (boiler) is it not an exposed conductive part?



Nope - read the definition - how can the pipe become an exposed part when it doesn't form part of the installation


Well I would say it is as much an exposed conductive part of the installation as the boiler casing? With a metallic connection to earthed equipment the pipe could become live if there is failure of basic insulation, say within the boiler?

If a conductive part (pipe) is not metallicaly connected to earthed equipment, and is said to be an extraneous conductive part, but is connected to the earthing system by a bonding conductor does it then cease to be an extraneous conductive part and become an exposed conductive part?



Nope - it's still an extraneous conductive part - read the definition - it doesn't form part of th eelectrical installation, it's not electrical equipment etc



An extraneous conductive part I would say would be for example an old mains water pipe that feeds upto a loft header tank and has no type of connections to anything electrical, but then if it gets main bonded then its no longer extraneous, as a failure of basic insulation to earth in the rest of the installation will cause it to become live(if only for a short time perhaps) or so i'd have said.

Would be happy to be put right on this....Cheers.
 02 April 2013 02:29 PM
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AJJewsbury

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Well I would say it is as much an exposed conductive part of the installation as the boiler casing? With a metallic connection to earthed equipment the pipe could become live if there is failure of basic insulation, say within the boiler?

Yes, the pipe could become just as live during a fault as the true exposed-conductive-part (the boiler casing), but from a electrical point of view we don't really care. We earth the original exposed-conductive-part and ensure ADS when a fault occurs. That fact that there's other metalwork in contact with it doesn't change anything fundamental - in physical terms it just makes the exposed-conductive-part a bit bigger. BS 7671 doesn't have language to describe the situation because we don't have to do anything about it.

An extraneous conductive part I would say would be for example an old mains water pipe that feeds upto a loft header tank and has no type of connections to anything electrical

Agreed
but then if it gets main bonded then its no longer extraneous

Nope, it's still extraneous (otherwise you'd end up in a silly situation that adding a bond removed the need to bond it, so you could take the bond off, at which point it would become extraneous- again and so need re-bonding....)

as a failure of basic insulation to earth in the rest of the installation will cause it to become live(if only for a short time perhaps) or so i'd have said.

There's nothing in the definition of an extraneous-conductive-part to say that it can't also be exposed to a potential from within the installation...

- Andy.
 02 April 2013 03:04 PM
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weirdbeard

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Originally posted by: AJJewsbury

- in physical terms it just makes the exposed-conductive-part a bit bigger. BS 7671 doesn't have language to describe the situation because we don't have to do anything about it.


Hi Andy, agree with you there, the pipes are an exposed conductive part.



but then if it gets main bonded then its no longer extraneous


Nope, it's still extraneous (otherwise you'd end up in a silly situation that adding a bond removed the need to bond it, so you could take the bond off, at which point it would become extraneous- again and so need re-bonding....)


Indeed

I guess thats one of the reasons when a connection to an extraneous conductive part is made we have labels saying 'safety electrical connection do not remove' !




as a failure of basic insulation to earth in the rest of the installation will cause it to become live(if only for a short time perhaps) or so i'd have said.


There's nothing in the definition of an extraneous-conductive-part to say that it can't also be exposed to a potential from within the installation...


.

Not entirely sure what you mean there!

Cheers.
 02 April 2013 03:12 PM
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OMS

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Originally posted by: weirdbeard

Originally posted by: OMS



Originally posted by: weirdbeard

Can there actually be such a thing as an extraneous conductive part in a a properly earthed and bonded installation or do extraneous conductive parts only exist on paper before an installation is installed? (not including installations that are not properly designed and/or installed)

Nope - they are real, they exist - in many forms.


Hi OMS, could you give examples?

OK - first think of the definition of extraneous - the bit about introducing a potential, usually earth potential - then forget the bit about earth potential and consider any potential - now think of say an external compresor house forming part of an energy centre and delivering compressed gas to several buildings. It does not supply any electrical equipment - it will do two things- introduce the potential of the MET in another building that it serves. Ditto for steam mains, medical gas mains, etc etc. They are not exposed conductive parts - therefore they remain extraneous conductive parts by definition

If a conductive part (pipe) is metallicaly connected to earthed equipment (boiler) is it not an exposed conductive part?

Nope - read the definition - how can the pipe become an exposed part when it doesn't form part of the installation


Well I would say it is as much an exposed conductive part of the installation as the boiler casing? With a metallic connection to earthed equipment the pipe could become live if there is failure of basic insulation, say within the boiler?

As I said, read the definitions - the boiler case is exposed because it is (electrical) equipment by definition. The pipe will go hazardous life, ADS will occur - that still hasn't made it an exposed part

If a conductive part (pipe) is not metallicaly connected to earthed equipment, and is said to be an extraneous conductive part, but is connected to the earthing system by a bonding conductor does it then cease to be an extraneous conductive part and become an exposed conductive part?

Nope - it's still an extraneous conductive part - read the definition - it doesn't form part of th eelectrical installation, it's not electrical equipment etc



An extraneous conductive part I would say would be for example an old mains water pipe that feeds upto a loft header tank and has no type of connections to anything electrical, but then if it gets main bonded then its no longer extraneous, as a failure of basic insulation to earth in the rest of the installation will cause it to become live(if only for a short time perhaps) or so i'd have said.

See my initial example of the compressed air line - if it's bonded it remains extraneous as it's capable of introducing a potential, not just earth potential - and it doesn't form part of (electrical) equipment

Would be happy to be put right on this....Cheers.


Regards

OMS

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 02 April 2013 04:13 PM
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weirdbeard

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Originally posted by: OMS


An extraneous conductive part I would say would be for example an old mains water pipe that feeds upto a loft header tank and has no type of connections to anything electrical, but then if it gets main bonded then its no longer extraneous, as a failure of basic insulation to earth in the rest of the installation will cause it to become live(if only for a short time perhaps) or so i'd have said.



See my initial example of the compressed air line - if it's bonded it remains extraneous as it's capable of introducing a potential, not just earth potential - and it doesn't form part of (electrical) equipment





Thanks for taking the time OMS, but surely by attaching a bonding conductor from the MET to an extraneous conductive part it then becomes part of the electrical equipment and can become live if there is a failure of basic insulation as a result of this connection, therefore would satisfy the definition of an exposed conductive part?

Taking the simple example of a water pipe in a house this could in theory be used as a protective conductor according to 543.2.6, so in which case would be definitely become part of the electrical equipment.

So going back to my original point -theoretically and pedantically speaking once there is an electrical connection to a conductive part it is no longer extraneous - or shall we agree to disagree?
 02 April 2013 04:20 PM
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AJJewsbury

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but surely by attaching a bonding conductor from the MET to an extraneous conductive part it then becomes part of the electrical equipment and can become live if there is a failure of basic insulation as a result of this connection, therefore would satisfy the definition of an exposed conductive part?

No, the bonding conductor and clamp are part of the electrical installation, the pipe isn't. It might be connected to the electrical installation, but it remains a part of the plumbing system.

Taking the simple example of a water pipe in a house this could in theory be used as a protective conductor according to 543.2.6, so in which case would be definitely become part of the electrical equipment.

Indeed, but a c.p.c. (which that length of pipe would become) isn't of itself either an exposed-conductive-part nor an extraneous-conductive-part.

-theoretically and pedantically speaking once there is an electrical connection to a conductive part it is no longer extraneous

No, as even when it's bonded, it still retains its physical ability to introduce a potential into the installation (or location) - bonding might reduce the magnitude of that potential difference, but unless you can find a bonding conductor with absolutely zero resistance it's never going to eliminate it.

- Andy.
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