Extraneous conductive part

[studentspark]

A metal water pipe enters the building , Its a Extraneous Conductive part (ECP) so needs Main protective bonding to the MET.

That same pipe, has a branch off it which then goes back under the floor (buried) and re appears in another room in the same house. (1) Does the second appearance of the pipe also need bonded back to the MET?
or would a supplementary bond be correct?

This pipe then goes back under ground to an out building which has a sub board powered from the main house.

This same pipe appears in the out building,
Should that pipe be protected by a supplementary bond (2) a TT earth (3) or A MPB (4)


Would it still be an Extraneous CP if it did not go under ground? (5)
Basically as it only travels through air, it can't pick up a potential?
and would that be a TT SPB or a MPB

MPB-1

• studentspark
• 23 Jan 2020

Hope that makes some sense

Thanks

 

[EFLImpudence]

A metal water pipe enters the building , Its a Extraneous Conductive part (ECP) so needs Main protective bonding to the MET.

Ok.

[hat same pipe, has a branch off it which then goes back under the floor (buried) and re appears in another room in the same house. (1) Does the second appearance of the pipe also need bonded back to the MET?

Not if it is connected satisfactorily to the other pipe and the MET.

or would a supplementary bond be correct?

It might need Supplementary Bonding if in a bathroom; otherwise not.

This pipe then goes back under ground to an out building which has a sub board powered from the main house.
This same pipe appears in the out building,
Should that pipe be protected by a supplementary bond (2) a TT earth (3) or A MPB (4)

It will need MPB to the local earth bar.

As it is connected to the house MET it may be used AS the MPB to the house MET, so there isn't much point having TT in the outbuilding.
The electrode will just be another extraneous-c-p

Would it still be an Extraneous CP if it did not go under ground? (5)
Basically as it only travels through air, it can't pick up a potential?
and would that be a TT SPB or a MPB

Extraneous to the outbuilding yes, but once MPB to the outbuilding board is fitted it will then BE the MPB to the house MET.

 

[JohnD]

homework, eh?

 

[flameport]

1 - Yes, but that could be bonded by virtue of it being the same metal pipe is already connected elsewhere. Bonding conductors do not have to be green/yellow wires. Testing required to confirm.

2 - Bonding required.
Either to the consumer unit in the second building if it has it's own TT earth,
or connecting it to the MET in the main building and using the earth connection from there.

Whether items are extraneous or not is determined by testing - being in the air/ground or whatever isn't particularly relevant.

 

[studentspark]

Thank you for your help, really good to clarify these things.

 

[JohnW2]

Whether items are extraneous or not is determined by testing - being in the air/ground or whatever isn't particularly relevant.

As I've often observed, the 'testing' is not really foolproof, and that there are certainly situations in which the fact that it is 'in the ground' can be relevant to one's decision as to whether it needs to be considered as an extraneous-c-p (hence needing bonding),

As I have described before, I have a gas (LPG) supply pipe which changes from plastic to metal 'underground', in a deep pile of gravel and sand, before entering my house. If undertaken during a decent dry spell, your (or EFLI's) tests would probably result in the conclusion that the incoming pipe was not an extraneous-c-p, and hence did not need main bonding - but if you repeated the tests during a 'wet spell' you would very probably come to a different conclusion.

I therefore would say that this is an example of a situation in which it is not only 'relevant', but actually important, to consider the fact that the pipe travels underground when deciding whether it should be regarded as a (potential') extraneous-c-p (and therefore bonded).

As with so many things, I think it comes down to the need for common sense, rather than a blind assumption that some 'generic' approach will always be appropriate.

Kind Regards, John

 

[studentspark]

This same pipe appears in the out building,
Should that pipe be protected by a supplementary bond (2) a TT earth (3) or A MPB (4)

It will need MPB to the local earth bar.

As it is connected to the house MET it may be used AS the MPB to the house MET, so there isn't much point having TT in the outbuilding.

The electrode will just be another extraneous-c-p

Am I getting this wrong
EFLI you say the pipe in the second location should be MPB to the local earth bar (CU in second building)?
But this pipe is already a protective bond between the two locations.

Basically this pipe could be seen as a green and yellow conductor between the two buildings.
as this pipe is a protective bond from the main house to the second building, so a separate connection does not need to be made from the second to first building

2 - Bonding required.
Either to the consumer unit in the second building if it has it's own TT earth,
or connecting it to the MET in the main building and using the earth connection from there.

Is this suggesting that a second connection need to be made to the pipe in the second building back to the main MET?

 

[EFLImpudence]

Am I getting this wrong
EFLI you say the pipe in the second location should be MPB to the local earth bar (CU in second building)?

Assuming the water pipe is continuous metal, it will be an extraneous-c-p to the outbuilding - both because it emerges from the ground elsewhere and it will become live with a fault in the house - therefore it must be Main Bonded to the OB CU.

But this pipe is already a protective bond between the two locations.

Not until it is bonded to the OB CU.

Basically this pipe could be seen as a green and yellow conductor between the two buildings.

After bonding to the OB CU, yes.

as this pipe is a protective bond from the main house to the second building, so a separate connection does not need to be made from the second to first building

Correct. The pipe may - is allowed to be - the MPB.

Is this suggesting that a second connection need to be made to the pipe in the second building back to the main MET?

No.

The usual reason for making an OB TT is to avoid having to have a large MPB back to the house, but you already have the pipe.

 

[studentspark]

Thanks EFLImpudence, really appreciate your help.
There is something about MPB, which constantly make me unsure.

 

[JohnW2]

Thanks EFLImpudence, really appreciate your help. There is something about MPB, which constantly make me unsure.

One relevant point that EFLI made was that if one has a metal pipe, adequate to be used as a bonding conductor, between the main house and outhouse, there is little reason to TT the outhouse.

The one point (of TTing the outhouse) that some may make is that it would help to bring the potential of the ground surrounding the outhouse up to something approaching the potential of the pipe - which, under rare supply fault conditions with a TN-C-S supply could be at a potential considerably above that of 'true earth'. This would at least partially address the potential hazard facing a person standing on ground outside of the outbuilding whilst at the same time touching something 'earthed' (to the local MET) within the outbuilding (during those very rare fault conditions).

Kind Regards, John

 

[EFLImpudence]

The one point (of TTing the outhouse) that some may make is that it would help to bring the potential of the ground surrounding the outhouse up to something approaching the potential of the pipe

Some might make that point but a single electrode is unlikely to do that.


Another thing I often ask is -

"What if the main house was larger and the back door of the house was where the outbuilding door is?"

Would anyone propose TTing that room and/or bonding the ground?

 

[JohnW2]

Some might make that point but a single electrode is unlikely to do that.

Well, it's bound to do it to some extent, but how great that extent would be in practice, I don't know. I can't see it doing any harm, so I suppose it would be 'better than nothing' (i.e. would raise the potential of the nearby ground at least a bit). However, we're really into 'bernard territory' here - since the chances of one standing with one foot outside of an outhouse and a hand inside it (touching something relevant) at the very moment that there was a TN-C-S 'lost neutral' surely must qualify as 'vanishingly small'?!

Another thing I often ask is - "What if the main house was larger and the back door of the house was where the outbuilding door is?" ... Would anyone propose TTing that room and/or bonding the ground?

I gave up a long time ago trying to predict 'what some people might propose'

Of course (as with outside taps) the theoretical hazard (again a 'vanishingly small' risk) faced by someone standing on the ground outside of a house whilst touching something connected to that house's TN-C-S earthing system is exactly the same with a house as with an outhouse, regardless of how big the house it or where the door is!

Kind Regards, John