Earth in wires

[JohnW2]

As to twin and earth cable it is not coloured green and yellow so there is little to stop the core from being used for another use except that the centre core is not double insulated so it would need to be in trunking or conduit.

As RF has said, it's not insulated at all, only sheathed, and I don't think that would be theoretically acceptable as a live conductor, even within conduit.

Kind Regards, John

 

[JohnW2]

As I see it, it makes no difference where it gets it's earth, though really needs to be from it's own circuit - not borrowed from another. Earth is is earth. The wiring centre could supply the earth for the programmer.

As I said, if the cable in question is connecting JBs/programmers/wiring centres (all of which will usually have multiple cables going to them), then it may sometimes be do-able.

However, this issue is most frequently raised (or encountered!) when people want to wire CH components which require L, S/L and N (some thermostats, boilers etc.), or PIRs or timer fans, but only have 3-core flex to hand. In such cases, it's unlikely that the component will be getting a CPC/'earth' conductor from anywhere else.

Kind Regards, John

 

[sparkwright]

Ah, I see what you mean.

 

[ericmark]

Where I have seen green/yellow used as line is with a Class II thermostat clamped to the side of the cistern. Clearly with fixed wiring wrong the same as supply to ceiling rose but this was flex from a local adaptable box to thermostat same as with ceiling rose to lamp holder.

I felt this was totally wrong it would be so easy when replacing the thermostat to put the earth coloured wire to earth and make the cistern live. One hopes the brown sleeve never falls off as that is the only thing which would stop such an error.

To me even if the BS7671:2008 does allow over sleeving of earth coloured wires it is very bad practice and for an organisation which calls them selves the electrical safety council to tell there scheme members they can over sleeve earth coloured wires is rather surprising there is no way that can be safe.

 

[Risteard]

The Electrical Safety Council (which does not have scheme members, as it belongs to the same parent company as the NICEIC and is not a scheme of its own right) could not advise anything other than that it is permitted (except for single-core cables), because it IS permitted. I seem to remember that it was not permissible under the 16th Edition, however - but would need to dig out my copy to confirm that this was indeed the case.

I also disagree that it is unsafe. Before breaking into a cable you have a duty to confirm what a conductor does, and surely inspection and testing will also show that it isn't what it has been connected to. The "bang test" isn't an approved method, after all.

 

[JohnW2]

The Electrical Safety Council (which does not have scheme members, as it belongs to the same parent company as the NICEIC and is not a scheme of its own right) could not advise anything other than that it is permitted (except for single-core cables), because it IS permitted.

As I've said, there is (at least to my mind) no doubt that it is permissible per BS7671 (except, as you say, for G/Y singles) - but that doesn't make me, or many others, particularly comfortable about the practice.

I also disagree that it is unsafe. Before breaking into a cable you have a duty to confirm what a conductor does, and surely inspection and testing will also show that it isn't what it has been connected to. The "bang test" isn't an approved method, after all.

That's theoretically true, and if you could promise me that everyone always checks a G/Y conductor to make sure that it really is a CPC (and not a live conductor), then I'd agree that it wouldn't be 'unsafe'. If you can't (which you can't!) make that promise, then it's bound to be 'less safe' than if it were not allowed. It's not really literally 'breaking in' to a G/Y conductor (which is probably very rare) which concerns me most but, rather, people forgetting to include (or not even knowing that they should include) the over-sleeving at terminations (which they frequently do with every other colour of over-sleeving). Many of us have seen bare CPCs of T&E used as a live conductor for such things, with no sleeving of any colour, so people capable of doing that presumably would also be capable of leaving a G/Y-insulated core of flex unsleeved in such a situation.

Kind Regards, John