Slightly unusual mains cold water supply

[RF Lighting]

Hello all. I'm working on a job at the moment which has had the mains cold water supply altered about and is need of main bonding.

There is a lead pipe coming out of the floor which is the main supply to the building. It used to feed straight into the old stop tap and out to the rest of the building.

As you can see this has been cut back and joined with an insulated connector before the stop tap.

How would you bond this installation?

 

[holmslaw]

..

 

[JohnW2]

As you can see this has been cut back and joined with an insulated connector before the stop tap.
How would you bond this installation?

This is a more extreme example of my water supply situation, the bonding of which we discussed at length a little while ago, and it raises all 'those questions' about the intent of an MPB [if you recall, I have a plastic interuption in the copper piping about 1 metre from the water meter].

I suspect we are all going to say that you need at least to bond to the lead pipe. If one takes the accepted view that the one and only purpose of primary bonding is to minimise any potential difference between the MET/CPCs and a potential (earth potential) introduced by an extraneous conductive part (the lead pipe), then that would presumably be all you'd need to do.

I also suspect that most people (like Holmslaw) would say that one should also extend the same bonding conductor (or possibly add a separate strap) to bridge across the plastic connector, and that is certainly what I would say. To my mind, that makes total sense, ensuring that pipework in the household is roughly at the same potential as the electrical installation's CPCs - but that connection to the copper pipework does not seem to qualify as 'main bonding' (and may well not be required by the regs), because that pipework is not extraneous and obviously cannot itself introduce any potential into the property (within which it is entirely contained).

If you were to suggest that you might only bond to the copper pipe, then you'd probably find yousrelf on the receiving ends of the same screams as when I toyed with idea of moving my main bonding about 500mm further from the water meter, so that it was on the 'house' side of the plastic interruption. If you did that, you would, admittedly have about two inches of 'unbonded' extraneous metal!!

One other point in passing. The design of some of those MDPE type plastic fittings (and associated collars/bushes etc.) is such that the copper pipe could possibly be going all the way through and touching the lead pipe. However, I don't think that alters any of the above, provided you bond at least to the lead pipe.

Kind Regards, John

 

[Taylortwocities]

Connect to the lead pipe and bridge across the plastic fitting to the copper pipe. That way you ensure the main earth bonding is not dependent on the whim of some deaf and dumber.

I am constantly surprised about your lack of knowledge.

What on earth (excuse the pun) is the point of bridging to the incoming water main (the lead pipe)? The plastic junction will insulate the incoming main from the rest in exactly the same way as if the water main were a plastic pipe.

The equipotential BONDING should go from the MET to the extraneous conductive parts of the installation. In this case that is the copper pipes that run from the stop cock to the rest of the house. The BONDING is connected above the stop cock <600mm.

EDIT: Having just seen John's response. The purpose of bonding is to keep all of the internal pipework at the same potential. If you just bond to the lead pipe then the internal pipework is still floating with respect to the MET. That would mean that the requirements for EEBADS and ADoS are not met.

If you bridge then you may introduce a potentail from outside. Better to let the junction be an insulator.

 

[JohnW2]

I knew this would happen ....

The equipotential BONDING should go from the MET to the extraneous conductive parts of the installation.

Indeed so.

In this case that is the copper pipes that run from the stop cock to the rest of the house.

I really do not understand how you can regard the copper pipework as an 'extraneous conductive part', as defined in the regs. There is no way in which it can introduce a potential into the house, since it is entirely contained within the house and is, as you've pointed out, insulated from the tiny, but true, extraneous conductive part (the lead pipe) by a plastic connector (which lead pipe, silly though it might be, very probably does technically need bonding in order to comply with BS7671 - even though, as you point out, it probably decreases safety by increasing the chance of a potential being introduced into the house).

As I've just written, I certainly would want my MET connected to the copper pipework throughout my house, but don't think that, in the situation described (or my house!), that can be described as 'main bonding'. It has an entirely different purpose from main bonding.

Kind Regards, John
edit x2: typos corrected!

 

[flameport]

Main protective bonding conductors are connected to extraneous conductive parts. Therefore the lead pipe should be connected.

If the copper is electrically connected to the lead through that coupling, then the copper is also en extraneous conductive part. However if the lead is already connected, then nothing is gained by also connecting to the copper.
If the copper is not electrically connected to the lead, it is not an extraneous conductive part, and therefore no bonding required.

If the small section of lead pipe was covered up with cement or concrete, nothing would be an extraneous conductive part and so no protective bonding required at all.

 

[JohnW2]

If the copper is electrically connected to the lead through that coupling, then the copper is also en extraneous conductive part. However if the lead is already connected, then nothing is gained by also connecting to the copper.

I'm glad that we are agreed as regards main bonding.

However, as regards the above quote, although it is nothing to do with 'main bonding', and has a totally different purpose, do you not agree with my desire to have the house's pipework connected to the electrical installation's CPCs. Admittedly, that will almost certainly happen incidentally, as a result of the CPCs of central heating electrics, immersion heaters etc, but I would still be that much more comfortable if I could see a fat piece of G/Y from MET to the house's pipework - wouldn't you?

Kind Regards, John.

 

[EFLImpudence]

If only Mr.Cockburn 'were' here. He'd 'know'.

 

[JohnW2]

Only just seen this edit ....

EDIT: Having just seen John's response. The purpose of bonding is to keep all of the internal pipework at the same potential. If you just bond to the lead pipe then the internal pipework is still floating with respect to the MET. That would mean that the requirements for EEBADS and ADoS are not met.

As I've said, I certainly want my internal pipework not only all at the same potential, but also at the potential of the MET (hence installation CPCs). However, this is not what main bonding is about. Furthermore, I'm not entirely sure what part of BS7671 actually requires (in generall) the 'supplementary bonding' of pipework which you and I clearly would like to see.

Kind Regards, John

 

[JohnW2]

If only Mr.Cockburn 'were' here. He'd 'know'.

I have no doubt that he would

I think the serious point which comes out of this is how much confusion there actually is in so many people's minds about bonding and earthing - with expressions of surprise about 'lack of knowledge' coming in the same breath as statements suggestive of somewhat confused knowledge.

[and I still think that the requirement for 'main bonding' of a TT installation is verging on (or...) the silly ]

Kind Regards, John

 

[ban-all-sheds]

.....my desire to have the house's pipework connected to the electrical installation's CPCs....

You are David Cockhead^H^H^H^Hburn and I claim my £5.

 

[matt1e]

What on earth (excuse the pun) is the point of bridging to the incoming water main (the lead pipe)? The plastic junction will insulate the incoming main from the rest in exactly the same way as if the water main were a plastic pipe.

The equipotential BONDING should go from the MET to the extraneous conductive parts of the installation. In this case that is the copper pipes that run from the stop cock to the rest of the house. The BONDING is connected above the stop cock <600mm.

EDIT: Having just seen John's response. The purpose of bonding is to keep all of the internal pipework at the same potential. If you just bond to the lead pipe then the internal pipework is still floating with respect to the MET. That would mean that the requirements for EEBADS and ADoS are not met.

If you bridge then you may introduce a potentail from outside. Better to let the junction be an insulator.

I agree with all the above, and also to add that unless the stopcock is in a bath/shower room then there would be no requirment to bond the lead pipe anyway

 

[ban-all-sheds]

If you just bond to the lead pipe then the internal pipework is still floating with respect to the MET.

So would be metal door handles, coat hooks...

That would mean that the requirements for EEBADS and ADoS are not met.

What do those requirements say you should do to metal items which are neither exposed conductive parts nor extraneous conductive parts?

 

[westie101]

In the case of a lost DNO earth, ot a TT earth or a PME lost neutral/earth, followed by a live to earth fault (except in the PME case where normal conditions will affect it) think Faraday Cage, that's all it is about!

The actual requirements for bonding a TN-C-S supply are dictated by the PME regulations (which the wiring regs have to match) in the other supply methods it is more a case of following good practice as dictated by the PME regs

 

[RF Lighting]

Intresting stuff.

I already have my own idea of how this should be bonded, but I thought I'd jusrt see what others thought too.

Personally I'd bond the lead pipe as it comes out of the floor. It is a metal pipe in the ground so will be at a potential, and although the risk presented by it is tiny, bonding it is still the right thing to do.

As for the installation pipework, although there is an insulating connector, the pipes are full of water, which may conduct and leave the copper piping at a different potential, so bonding this would be a good idea too.

I'll have to try an IR and continuity across this joint next time I'm there just out of interest.

Does that sound like a plan?