Using earth wire in 3-core cable (for Nest install)

[Jackrae]

you can use the "earth" wire as a power conductor in a multicore.

Green/yellow cores are not an "earth" wire unless you do not identify them as being anything else.

Two negatives and possible maybe in the same sentence - now i am confused.

I presume (a dangerous habit ) that G/Y referred to as an earth wire is a convention.

I can understand where the arguments of single core versus multicore comes from and it makes "logical" sense. Any single G/Y located in a conduit, raceway etc might be assumed to be an earth cable, whereas a sheathed multicore will display no colours until one gets to the open ends, at which point over colouring or ID tags will clarify each core's purpose.

 

[JohnW2]

I can understand where the arguments of single core versus multicore comes from and it makes "logical" sense. Any single G/Y located in a conduit, raceway etc might be assumed to be an earth cable, whereas a sheathed multicore will display no colours until one gets to the open ends, at which point over colouring or ID tags will clarify each core's purpose.

Yes, that makes sense. However (although no-one should really need to do it), I see nothing in the regs which prevents a blue (or black, in old colours) single being over-sleeved just at the ends and used as a live conductor - so, whilst the regs might make 'logical sense' in relation to G/Y singles, that 'logical sense' seems somewhat limited in scope!

Kind Regards, John

 

[ericmark]

1) I personally feel that green/yellow should never be used for anything but earth.
2) On a previous post there was a link to I think the Electrical Safety Councils website where they said in multi-core cables one is permitted to over sleeve the green/yellow cable.

So if I was doing the job I would not use green/yellow for anything but earth and would never over sleeve, but if I was inspecting some one else's work I could not condemn their work if a green/yellow was over sleeved.

Bare copper cables or even stainless steel can be used as conductors with SELV you only have to look as 12 volt lamps where wires are run across the ceiling allowing you to place lamps where you want or two arms of a desk lamp are also the conductors.

The earth in twin and earth is insulated but not double insulated so there would be a problem with low voltage but not extra low voltage there is no green/yellow on the wire so you can use it as you want.

Even with low voltage we should never assume a bare wire or even a green/yellow wire is earth we should always test that earth that's why we have an earth loop impedance meter in out test set. We are suppose to use the meters they are not just to make us look professional.

I personally think using either the bare copper on a twin and earth or a green/yellow cable for anything but earth is wrong. I know with live cables danger could exist where conductors are not identified correctly but be it a phase or neutral they are all live conductors and should there for be insulated at all points.

Earth is the odd one out it may be connected to items which can be touched.

I remember people coming to me and stating "I've checked and your not allowed to do that." where advice had been given but some thing had been missed out in the telling. As a result even though I do not like the idea of over sleeving I will never the less point out it does not actually contrive regulations and others are free to do it if they wish.

 

[JohnW2]

So if I was doing the job I would not use green/yellow for anything but earth and would never over sleeve, but if I was inspecting some one else's work I could not condemn their work if a green/yellow was over sleeved.

I suspect that is how most of us feel. Indeed, I also suspect that most of us would say that we regarded the use of an (over-sleeved) G/Y as a live conductor as being 'not good practice'.

I suppose that, in some senses, that makes many of us a bit 'arrogant'. If the regs allow the practice, then 'lots of clever people' presumably think it's OK, so one might question whether should really call it 'not good practice' (but I, for one, certainly would ).

Kind Regards, John

 

[Jackrae]

"Not good procedure" versus "Not good practice"

 

[stillp]

If the regs allow the practice, then 'lots of clever people' presumably think it's OK

The regs don't disallow all sorts of stupid/dangerous/foolhardy practices. That's not because the 'clever people' think those practices are OK, but because there's no point in writing a regulation to forbid something that no-one in their right mind would contemplate.


Who was it who used to point out that genius has limits, stupidity doesn't?

 

[ban-all-sheds]

"Not good procedure" versus "Not good practice"

What about "good workmanship"?

 

[JohnW2]

If the regs allow the practice, then 'lots of clever people' presumably think it's OK

The regs don't disallow all sorts of stupid/dangerous/foolhardy practices. That's not because the 'clever people' think those practices are OK, but because there's no point in writing a regulation to forbid something that no-one in their right mind would contemplate.

Whilst that is probably not an unreasonable general view, I'm not sure that's really applicable in the present context. They have gone to the trouble of specifically disallowing the use of a G/Y single as anything other than a protective conductor which, by implication, means that the same does not apply to the G/Y core of a multi-core cable. Are you suggesting that 'no-one in their right mind' would contemplate using a G/Y core of a multi-core cable as a live conductor, whereas the same is not true of a G/Y single (I would personally have thought the opposite, if anything).

More generally, I would add that (as I need not tell you) that there are countless things which BS7671 specifically 'disallows' which one would certainly hope that 'no-one in their right mind' would contemplate doing!

Kind Regards, John

 

[JohnW2]

"Not good procedure" versus "Not good practice"

What about "good workmanship"?

I don't think that the vocabulary is really the issue. The question remains as to how appropriate it is for us to regard something as "not good practice/ procedure/ workmanship" if it is something which is 'allowed' (or 'not disallowed') by the regs.

In the case of 'good workmanship', which BS7671 calls for, there clearly would be a contradiction in the regs if something allowed by the regs were also regarded as 'not good workmanship'.

Kind Regards, John

 

[stillp]

In my professional world, G/Y is specifically reserved for protective conductors, whether single conductors or part of a multicore cable.
Perhaps the JPEL members felt it was unnecessary to make such a general requirement.

 

[JohnW2]

In my professional world, G/Y is specifically reserved for protective conductors, whether single conductors or part of a multicore cable. Perhaps the JPEL members felt it was unnecessary to make such a general requirement.

Exactly. If you substitute my 'lots of clever people' for your 'JPEL members', then I think we're both essentially saying the same thing. ... which leads me to continue to ask how appropriate it is for 'us' to regard something as 'bad practice' if JPEL members felt it was unnecessary to disallow it.

Having said all that, despite BS7671/JPEL members, I personally am still inclined to regard it as 'bad practice' (certainly 'non-ideal practice'), even if I have to confess that, in the relatively distant past, I've been known to do it with 3-core flex, usually when feeding timer fans or PIRs.

Kind Regards, John

 

[stillp]

No, you're misunderstnding me John. Perhaps I should have written (again) that "Perhaps the JPEL members felt it was unnecessary to make such a general requirement because nobody would need to be told that they must not use G/Y for any purpose other than a protective conductor".

 

[JohnW2]

No, you're misunderstnding me John. Perhaps I should have written (again) that "Perhaps the JPEL members felt it was unnecessary to make such a general requirement because nobody would need to be told that they must not use G/Y for any purpose other than a protective conductor".

Oh, I see - apologies for misunderstanding. However, I remain a little confused - why would they think that no-one needed be told that they must not use a G/Y core of a multi-core cable for anything other than a protective conductor when they apparently did think that people needed to be told that a G/Y single must not be used as anything other than a protective conductor? Maybe I'm being dim, but to me this 'singling out' (sorry ) of G/Y singles they did seems to have an 'obvious implication'.

Kind Regards, John

 

[stillp]

Now I have BS7671 in front of me (it's not a standard I use very often), I don't know why you see a dilemma. 514.4.2 begins with the sentence "The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor and this combination shall not be used for any other purpose".
That's a perfectly clear requirement, which does not distinguish between conductors in a multicore, or singles. Unfortunately they then confused the issue somewhat by a specific requirement dealing with singles, but that (although apparently confusing to some) does not undermine the requirement in the first sentence.
I suspect the addition dealing with singles is there as a way to introduce the exception that allows a single G/Y, sleeved blue at the ends, to be used as a PEN conductor, but there is no need to try to understand what the members of JPEL64 were thinking, just read the words that are there.
Green and yellow = protective conductor.

Simples.

 

[JohnW2]

Now I have BS7671 in front of me (it's not a standard I use very often), I don't know why you see a dilemma. 514.4.2 begins with the sentence "The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor and this combination shall not be used for any other purpose". ... That's a perfectly clear requirement, which does not distinguish between conductors in a multicore, or singles. Unfortunately they then confused the issue somewhat by a specific requirement dealing with singles, but that (although apparently confusing to some) does not undermine the requirement in the first sentence.

I believe you are missing a crucial point regarding that first sentence. If you look earlier in that section (it's my turn not be be close to my copy!) you will find that, as I've been saying in this thread, an acceptable form of 'identification' is over-sleeving at the ends (regardless of the insulation under that over-sleeving). Hence, a G/Y conductor over-sleeved with, say, brown is regarded as being 'identified as' a live conductor. That doesn't violate the requirements of that first sentence, since brown, not G/Y is being "used to identify" something which is not a protective conductor.

... there is no need to try to understand what the members of JPEL64 were thinking, just read the words that are there.
Green and yellow = protective conductor. Simples.

I agree - but, as above, I don't believe you have read (or, at least, fully assimilated) all the "words that are there" in the section.

Kind Regards, John