Earth Bonding trouble

[Coaster]

I have a copper rising main coming in from a concrete floor, which has a plastic elbow fitted, just before the stopcock.

I think I can just about get the earth strap between the stopcock and the offending plastic elbow, do i need 2 earth straps on each side of the elbow?

 

[PrenticeBoyofDerry]

So the plastic elbow is the supply side of the stop tap?
If so no need to bridge across the joint, if it was after the stop tap I would clamp just after the elbow joint.
You are aiming to bond the metal work within in the house not external to the property.

edit!

 

[RF Lighting]

Are you sure about that?

 

[PrenticeBoyofDerry]

I am/was and you cast doubt, may I ask why?
Oh I think I see why, I have edited!

 

[JohnW2]

So the plastic elbow is the supply side of the stop tap? If so no need to bridge across the joint, if it was after the stop tap I would clamp just after the elbow joint. You are aiming to bond the metal work within in the house not external to the property.

I'm sure that this the conventional, and many people would say sensible, wisdom. However, if the stop tap is insulated (by the plastic elbow) from the supply pipe, the pipework within the house is not an extraneous-conductive-part - hence some would argue doesn't need main bonding. Some would even argue that to 'earth' such pipework within the house with a bonding conductor actually decreases safety!

Kind Regards, John.

 

[PrenticeBoyofDerry]

But surely that would make no difference as the aim is to bring the internal metal work to the same potential.
The external supply is not used as a path to earth.
The path to earth is made by the MET or earth busbar connection to the supply earth.
If the whole installation was in plastic fair enough.

 

[EFLImpudence]

I have a copper rising main coming in from a concrete floor, which has a plastic elbow fitted, just before the stopcock.

I think I can just about get the earth strap between the stopcock and the offending plastic elbow, do i need 2 earth straps on each side of the elbow?

Strictly speaking you need to 'main bond' (10mm conductor to Main Earth Terminal) the pipe which comes out of the ground.
How long is it? (from ground to plastic elbow)

Then you may need to 'supplementary bond' the pipework after the elbow but you may not - it depends.
Is it physically connected to other metal parts which exit the ground and enter the building? e.g gas pipe via a boiler.

 

[westie101]

However, if the stop tap is insulated (by the plastic elbow) from the supply pipe, the pipework within the house is not an extraneous-conductive-part

I would suggest that would only be the case if it could be proved by other means than supposition, that no part of the internal pipework was in contact with the greater mass of earth via the structure of the building.

 

[EFLImpudence]

the aim is to bring the internal metal work to the same potential.

Only if it has a potential itself.

The external supply is not used as a path to earth.

If you mean the pipe which exits the ground - it should be bonded, not earthed

The path to earth is made by the MET or earth busbar connection to the supply earth.

Yes.

If the whole installation was in plastic fair enough.

Well, yes obviously.

However, if the pipework in question is isolated - not very likely - then it should not be bonded.
If it is not isolated - very likely - then it should be supplementary bonded if necessary.

 

[JohnW2]

But surely that would make no difference as the aim is to bring the internal metal work to the same potential. The external supply is not used as a path to earth.
The path to earth is made by the MET or earth busbar connection to the supply earth.

If one could be certain (and that's the problem) that the internal pipework was insulated from all paths to earth (including, as has been said, a p;ath via a boiler and gas sipply pipe), then it would theoretically be safer to leave that pipework all 'floating' and not connected via bonding and the MET to earth.

The problem is that many people so not seem to fully understand this, so that the absence of main bonding could cause grief when it came to a PIR/EICRinspection!

Kind Regards, John.

 

[JohnW2]

Strictly speaking you need to 'main bond' (10mm conductor to Main Earth Terminal) the pipe which comes out of the ground.

Indeed, although it sounds as if it is a ridiculously short length of metal pipe, in which case main bonding of it would be a real Jobsworth matter!

Then you may need to 'supplementary bond' the pipework after the elbow but you may not - it depends. Is it physically connected to other metal parts which exit the ground and enter the building? e.g gas pipe via a boiler.

If the water pipework were itself reliably insulated from the incoming supply pipe (hence not an e-c-p), but connected to earth via boiler and gas supply pipe, then it would be just the gas supply pipe, not the water one, which would be an e-c-p and which would require main bonding.

Kind Regards, John.

 

[EFLImpudence]

Then you may need to 'supplementary bond' the pipework after the elbow but you may not - it depends. Is it physically connected to other metal parts which exit the ground and enter the building? e.g gas pipe via a boiler.

If the water pipework were itself reliably insulated from the incoming supply pipe (hence not an e-c-p), but connected to earth via boiler and gas supply pipe, then it would be just the gas supply pipe, not the water one, which would be an e-c-p and which would require main bonding.

 

[JohnW2]

However, if the stop tap is insulated (by the plastic elbow) from the supply pipe, the pipework within the house is not an extraneous-conductive-part

I would suggest that would only be the case if it could be proved by other means than supposition, that no part of the internal pipework was in contact with the greater mass of earth via the structure of the building.

If I may say so, that's an unusually theoretical/academic comment from you, westie - at least, in relation to a 'traditional' (brick or stone built) domestic property.

You are, of course, theoretically correct - but if there were any question of the structure of the building introducing a significantly low impedance path to earth potential, I would suggest that the question of whether or not the pipework were in contact with it would be the least of one's problems - since the entire structure of the building itself would then theoretically need to be bonded!

Kind Regards, John.

 

[westie101]

The reality of the beast is that it not unknown that in cases of lost neutral faults, it is not unknown for us to receive reports of shocks from taps etc in kitchens with concrete floors!
I have a plastic water pipe so bonding is to the internal water piping (TNC-S) but on the ground floor all the heating pipework is within the concrete floor screed, I would class that as being in contact with the general mass of earth!

 

[EFLImpudence]

on the ground floor all the heating pipework is within the concrete floor screed, I would class that as being in contact with the general mass of earth!

Central heating is one of the items listed as possible extraneous-conductive-parts in 411.3.1.2 and as such shall be main-bonded.