Slightly unusual mains cold water supply

[JohnW2]

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!

True, provided that one has complete faith in the fact that main bonding for other extraneous conductive parts is present, satisfactory and will never be removed. If you don't have that faith, there is a possibility that what you will have is a Faraday cage which, for example, is pervaded by earthed earthed gas pipework - which would be less reassuring! Admittedly, there will normally be an implicit connection between gas and water pipework (usually at a boiler), but even that is not guaranteed if some of the water pipework is plastic (or there is no gas boiler).

Kind Regards, John

 

[westie101]

What would you do if it was a plastic water pipe? Do that!
As it may/should/must get changed in the future (lead pipes are classed as not advisable due to health risks!

 

[westie101]

provided that one has complete faith in the fact that main bonding for other extraneous conductive parts is present

We have, by statute, to check they are in place before commencing a supply. If we come across an installation where they are disconnected we have the right, by statute, to disconnect the supply.

After that all we can do is rely on the electrical contractors and others working on a property to get it right. Which may be a vein hope.

 

[JohnW2]

[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

In common sense terms, you're obviously right - but I don't think there is any doubt that the lead pipe qualifies as an extraneous conductive part (as defined) and I haven't seen anything in BS7671 which exempts the need to main bond such an extraneous conductive part if it is only very short.

In a directly analgous situation, a few weeks back I tried to use that same 'common sense' argument in relation to my water supply, which has a plastic interruption less than 1 metre from the water meter - but most people here were sticking to the book and saying that failure to main bond that very small length of copper pipe would be non-compliant. Furthermore (a separate issue, but being discussed here) many of them also suggested that the bonding should also be extended to the household pipework by extending the bonding (or adding a strap) also to the house side of the plastic interruption.

Kind Regards, John

 

[JohnW2]

What would you do if it was a plastic water pipe? Do that!
As it may/should/must get changed in the future (lead pipes are classed as not advisable due to health risks!

We're tralking about the present. If the lead pipe were plastic, then there would be no extraneous conductive part, and hence obvioulsy no need for main bonding (of water supply). However, so long as there is an extraneous conductive part, no matter how short, BS7671 appears to theoretically require main bonding (even when silly, as in this case) - as people kept telling me in that other recent thread.

If the water supply arrangement changes in the future, the bonding requirements may also change - but I don't think one can claim an exemption from a regulation on the basis that what may happen in the future.

Kind Regards, John.

 

[JohnW2]

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?

As is probably apparent, that's exactly what I'd do (and have done, in the essentially similar situation in my house). There will, of course, be some here who will argue that bonding of the copper installation pipework is not necessary, regardless of the continuity across the pipe joint. They will say that if there is continuity, by virtue of water (unlikely to be usefully low resistance) or, as I suggested as a posibility, by contact between copper and lead within the fitting, then your bonding to the lead will still achieve the required main protective bonding. Some will also add that they do not feel a need for the installations pipework to be explicitly bonded; whilst probably true in terms of the regs, you will have seen that my 'comfort' would like it to be present.

Kind Regards, John.

 

[JohnW2]

.....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.

I would suggest (hope!) that my style (and, in some cases, knowledge or common sense) identifies me as a different person

As I wrote last night, I do think this discussion, and many others like it, illustrate the serious confusion which exists in relation to bonding and earthing. You've only got to look at this thread, let alone the others, to see intelligent people, many of whom are well-qualified or experienced and some of whom are practising electricians, offering very different opinions. I therefore feel (with one or two exceptions) that the common accusations that individuals are 'dim' because 'they do not understand bonding (and/or earthing)' are maybe inappropriate; a well-known saying about glasshouses and stones often comes to mind!

Kind Regards, John

 

[westie101]

I take the view that the primary connection must be to the copper pipework to comply with all the regs.
Connecting to the lead though theoretically required would serve no electrical purpose that I can see. (though it would no doubt make a good TT earth rod!)

The whole idea is not to follow regs blindly but to think and understand why these connections are made

To my mind, the purpose of the regs is to set a minimum standard and then allow the designer leeway to alter things if they can show that it is no less safe that strict adherence.
So, for example, if by having a bond more than 600mm away from the suggested point puts it on a plastic pipe, which is a nonsense moving it to the nearest point of contact with a copper pipe fully complies.

 

[JohnW2]

provided that one has complete faith in the fact that main bonding for other extraneous conductive parts is present

We have, by statute, to check they are in place before commencing a supply. If we come across an installation where they are disconnected we have the right, by statute, to disconnect the supply.

I'm sure that's right but, as you go on to say ...

After that all we can do is rely on the electrical contractors and others working on a property to get it right. Which may be a vein hope.

... and it is you who, only a few minutes ago, reminded us that the pipework arrangements "may/should/must be changed in the future".

Kind Regards, John.

 

[JohnW2]

I take the view that the primary connection must be to the copper pipework to comply with all the regs.
Connecting to the lead though theoretically required would serve no electrical purpose that I can see. (though it would no doubt make a good TT earth rod!)
The whole idea is not to follow regs blindly but to think and understand why these connections are made
To my mind, the purpose of the regs is to set a minimum standard and then allow the designer leeway to alter things if they can show that it is no less safe that strict adherence.

I wish it were as simple as that - since, eveything you're saying is common sense, and totally in keeping with arguments I have tried here in the past.

I think one issue is that many people believe, maybe correctly, that the one and only reason for BS7671 requiring main bonding of incoming pipes is to prevent those incoming pipes introducing a potential into the building which is different from the potential of the MET/CPCs. If you do take the view that this is the 'one any only' reason for the requirement, then it is only relevant (if at all) as far as the first non-conductive interuption in the pipework. In that sense, bonding to the copper after an interruption would not be 'main bonding' as far as BS7671 is concerned, and nor would it probably be required by BS7671.

So, for example, if by having a bond more than 600mm away from the suggested point puts it on a plastic pipe, which is a nonsense moving it to the nearest point of contact with a copper pipe fully complies.

That's the argument I tried here about my setup which has a plastic interruption about 1000mm from the water meter. Most people wanted me to main bond just that 1m of pipe (within 600mm of meter, per regs) and not necessarily bond the copper pipework going into the household. Opinions obvioulsy vary.

Kind Regards, John

 

[westie101]

It's not about common sense in anyway, it is more about designing an installation to comply with the minimum safety requirements and being able to show that electrically the choices made are correct.
It is not about blindly following the book!

 

[JohnW2]

It's not about common sense in anyway, it is more about designing an installation to comply with the minimum safety requirements and being able to show that electrically the choices made are correct.
It is not about blindly following the book!

Again, agreed. Maybe there are a lot here who believe in blindly following the book - since, when I suggested a similar approach ('common sense' and "being able to show that electrically the choices made are correct" are much the same in my book) for my house's installation, there were a lot of dissenting voices!

The regs themselves (particularly BS7671) may be part of the problem. If one ignores the theoretical requirement to bond the negligible and 'obvioulsy irrelevant' couple of inches of 'extraneous conductive part' in the case RFLighting asked about, I'm really not sure what regulations (particularly BS7671) have any 'minimum safety requirements' which require any 'main' bonding to this water installation. What am I missing?

Kind Regards, John.

 

[westie101]

Take it outside any regs, think of the Faraday Cage;

Do you want anyone, under fault conditions. to be hold of an electrical appliance that is live at 230V and then to touch another metal item* that is at or about earth potential?

* OK we can joke about door handles and the like, but for any danger there needs to be a current path.
There seems to be a total lack of thought to basic electrical theory in a lot of discussions on here.

Within the regs, as I stated elsewhere, it is a requirement of the PME regs! I'm no expert on the 17th edition, so will leave it to others to decide if they require this or not!

 

[JohnW2]

Take it outside any regs, think of the Faraday Cage;
Do you want anyone, under fault conditions. to be hold of an electrical appliance that is live at 230V and then to touch another metal item* that is at or about earth potential?

No, as I've said, I don't. That's why (despite all the ridicule it seems to generate) I want the pipework in my house explicity bonded to the electrical installation's MET (hence CPCs) by a fat bit of G/Y which I can see. However, this is not 'main bonding' as far as BS7671 is concerned, particularly when the (minute) incoming extraneous conductive part is insulated from both pipework and electrical installation (unless, that is, one puts in the main bonding to it, as theoretically required by BS7671!!)

* OK we can joke about door handles and the like, but for any danger there needs to be a current path.
There seems to be a total lack of thought to basic electrical theory in a lot of discussions on here.

Agreed. I'm not sure it's totally the fault of those here, since they are being 'fed' by the apparent requirements of BS7671.

Within the regs, as I stated elsewhere, it is a requirement of the PME regs! I'm no expert on the 17th edition, so will leave it to others to decide if they require this or not!

What is a requirement of the PME regs? Are you saying that those regs require bonding to pipework within a building even when that pipework is electrically insulted from any pipework entering the building from outside (i.e. that which aids my 'comfort)? If so, unless someone can put me right, I think that's something which is not theoretically required by BS7671 - not to mention the fact that some people here are saying that it's unnecessary or even undesirable.

Kind Regards, John

 

[westie101]

Bonding internal metal work is an absolute requirement of the PME regs, I'll get some quotes from them at work tomorrow.

That is in effect the most dangerous system if things are done wrong.

Think of the electrical effect of the loss of a neutral/earth prior to the mainfuse.
With any load switched on, any metalwork connected to the earth becomes live (draw it out on paper) (I've seen it)
Now if it could be proven that the water & gas systems in a property are totally insulated from earth, not bonding them would not be an issue.
However that is rarely (if ever the case) so there is potential difference and a current path from the live metalwork to earth via the person who is touching both!!
So if they are bonded to the metalwork that has become live there is no potential difference so no risk of shock.

Yes an RCD may disconnect the power but when regs were first written such things were rare, nor does it appear that that a change to these requirements has been needed.

It gets mentioned on here, the connection between the DNO earth terminal and any internal metalwork is not to connect the metal to earth, or provide an earth to the installation. It is to prevent the risk of potential (equipotential = everything at the same potential) differences in the case of a loss of the DNO earth.