Exporting TN-C-S to outbuilding - again!

[EFLImpudence]

Maybe, but if "it is not possible to determine the NON-extraneousness of the water supply pipe" then, per the word of 534.2.6, I don't think you can use it as a protective conductor for supplementary bonding in the manner you have described, since that reg only allows you to do that if it IS extraneous (it doesn't say 'bonded', it says 'extraneous'). If you don't know whether it is extraneous or not then, in terms of the way it's written, you cannot 'enjoy' the provisions of 534.2.6.

Home now with BGB.

543.2.6 but -

I can only suggest that because it is connected to the gas pipe and cpcs it is classed as part of the extraneous pipework in that it may be liable to introduce a potential (not necessarily Earth potential).

Is the gas pipe still extraneous at its boiler connection?

That would be a reason for 544.1.2

 

[JohnW2]

543.2.6 but -...

Indeed. Apologies. You must by now be aware that my (fast but) 2-finger typing very often results in 'adjacent character transpositions' - my most infamous ones (if I dont notice and correct them) probably being obvioulsy, taht and beacuse

I can only suggest that because it is connected to the gas pipe and cpcs it is classed as part of the extraneous pipework in that it may be liable to introduce a potential (not necessarily Earth potential). Is the gas pipe still extraneous at its boiler connection? That would be a reason for 544.1.2

Yes - but, as I suggested before, wouldn't that be the argument which says that every pipe, CPC, exposed-c-p or whatever which is in electrical continuity with something which is an extraneous-c-p must itself be treated as an extraneous-c-p? - which I wouldn't think was either appropriate or helpful, would it?

In any event, I'm not sure this really explains 544.1.2, since (if the water pipework is 'insulated' from the outside world) the only thing which is 'liable to introduce a potential' is the gas pipe, which will already be main bonded for that very reason. As above, it seems inappropriate (I might say 'daft'!) to suggest that anything/everything which is in electrical continuity with that (main bonded) gas pipe has to be regarded as an extraneous-c-p and therefore provided with its own, separate, main bonding.

If the water pipework is isolated from the outside world (by an insulating section) and therefore cannot, in itself, 'introduce a potential', then I might suggest that any 'bonding' applied to it should really be regarded as supplementary, rather than main, bonding.

Kind Regards, John

 

[EFLImpudence]

Yes - but, as I suggested before, wouldn't that be the argument which says that every pipe, CPC, exposed-c-p or whatever which is in electrical continuity with something which is an extraneous-c-p must itself be treated as an extraneous-c-p? - which I wouldn't think was either appropriate or helpful, would it?

True, except that a cpc will already be connected to the MET itself.
Any additional so-called bonding would only serve to increase the csa.

In any event, I'm not sure this really explains 544.1.2, since (if the water pipework is 'insulated' from the outside world) the only thing which is 'liable to introduce a potential' is the gas pipe, which will already be main bonded for that very reason. As above, it seems inappropriate (I might say 'daft'!) to suggest that anything/everything which is in electrical continuity with that (main bonded) gas pipe has to be regarded as an extraneous-c-p and therefore provided with its own, separate, main bonding.

True.

If the water pipework is isolated from the outside world (by an insulating section) and therefore cannot, in itself, 'introduce a potential', then I might suggest that any 'bonding' applied to it should really be regarded as supplementary, rather than main, bonding.

True.

Dunno, then.

 

[JohnW2]

True, except that a cpc will already be connected to the MET itself.

Indeed. By the same token, the water pipe will also be connected to the MET, via gas pipe and its bonding and/or CPCs (usually both) - either that, or if it's not connected to the MET via any of those routes (and is isolated from 'the outside world'), then the pipework is totally floating, hence wouldn't require any 'main bonding'!

True ....True .... True. Dunno, then.

This sounds 'orribly close to some sort of agreement

Kind Regards, John

 

[EFLImpudence]

We always agree when you're right.

I have read lots of threads on several forums and no one seems to know why 544.1.2 says what it does about insulating sections.

 

[JohnW2]

We always agree when you're right.

I have read lots of threads on several forums and no one seems to know why 544.1.2 says what it does about insulating sections.

It's a pretty ridiculous thing to have to suggest, but the most obvious explanation would be that whoever wrote it did not really understand the concept and purpose of main protective bonding!

Those who defend such things in the regs (and this is obviously not the only example) tend to wheel out the arguments along the lines that "the insulating section could be removed and replaced with metal". However, if we are going to try to anticipate all the things that might conceivably happen to the property in the future (and, as a result, do things which may introduce more hazards than they prevent, with the present status quo), then I think we probably need to 'give up'!

Kind Regards, John

 

[ban-all-sheds]

It's a pretty ridiculous thing to have to suggest, but the most obvious explanation would be that whoever wrote it did not really understand the concept and purpose of main protective bonding!

They hired David Cockburn...

 

[JohnW2]

A thought about detail has occurred to me, which applies to all these 'TTing an outbuilding' situations. In the very first post in this thread, the OP described the 'standard' way of isolating an oubuilding from the house's earthing system, when he wrote:

....3 core 6mm² SWA to outbuilding 25m away. SWA terminated in plastic box, no banjo fitted. Three cores carry on to plastic DB where only two cores are used as Line and Neutral. Outbuilding TT'd. ...

Assuming that the SWA armour was connected to the house's earth at the house end, that is essentially the advice that would normally be given to someone wanting to TT the outbuilding and 'isolate' it from the house's earth.

However, I suspect that many people will interpret "SWA terminated in plastic box" as referring to the use of an SWA gland, in the usual way. If that is done, the house earth will be connected to the external metal parts of the SWA gland in the outhouse, and the only thing stopping people touching them (potentially simultaneously with the local TT earth) will be the gland's 'boot', which is easily removed (without a tool) and could even slip on its own. Would that get past Mr Jobsworth, I wonder? If one wanted to avoid this issue, but without the hassle of enclosing the entire SWA gland in an insulating enclosure, then maybe it would be better to use a 'stuffing gland' (with nothing connected to the cable's armour at the outbuilding end), rather than an SWA gland?

Kind Regards, John