Earth in wires

[gasman1987]

I'm a heating engineer and if I was to wire the 10 way box and controls components I would always want to run a cable with the appropriate amount of cores including a earth, I always come across wires where they use the earth as a live wire . Can this be done

Most of the controls are double insulated and don't require a earth but do you need a earth in case you cut through a wire to trip the rcd ??


Thank you

 

[EFLImpudence]

I'm a heating engineer and if I was to wire the 10 way box and controls components I would always want to run a cable with the appropriate amount of cores including a earth, I always come across wires where they use the earth as a live wire . Can this be done

No. It cannot/should not be done.

Most of the controls are double insulated and don't require a earth but do you need a earth in case you cut through a wire to trip the rcd ??

That could be one reason, yes.
A CPC (earth wire) must be run to all points and, obviously, connected at the wiring centre and so to earth at the source.

 

[JohnW2]

I'm a heating engineer and if I was to wire the 10 way box and controls components I would always want to run a cable with the appropriate amount of cores including a earth, I always come across wires where they use the earth as a live wire . Can this be done. ... Most of the controls are double insulated and don't require a earth but do you need a earth in case you cut through a wire to trip the rcd ??

An old chestnut, which often/usually generates a lot of debate. An earth in any cable is desirable, for the reason you mention. Also, as far as the Wiring Regs are concerned, a CPC ('earth') should be run to every point or accessory in an installation, even if it is not (currently) actually needed (e.g. for a Class II / 'double insultaed' load/accessory).

The most contentious thing (which I imagine is essentially what uou are asking about) is the use of a green/yellow-insulated core (obviously designed to be CPC/earth) as a live core. If appropriately over-sleeved (with brown or red, if used as L) at the ends, it can just about be argued to be compliant with the regs, but I think that most people would agree that it's an absolutely 'orrible practice which should be avoided. Electricians would probably never do it, but those from other trades, and DIYers, sometimes do.

Kind Regards, John

 

[gasman1987]

I thought that this didn't comply with regs. I would say a lot of the older properties never do but from a maintenance point of view I always install a double insulated product but there is nothing protecting the cable.

 

[securespark]

I would say it does not comply.

If someone came along at a later date and chopped a JB into a cable to connect to the CPC (where there would be no marking to indicate change of use), that would be potentially lethal.

 

[JohnW2]

I would say it does not comply. ... If someone came along at a later date and chopped a JB into a cable to connect to the CPC (where there would be no marking to indicate change of use), that would be potentially lethal.

We've been through this many times before and, although I agree with what you say, one ends up being forced to agree that, 'orrible a practice though it is, is is not non-compliant with BS7671 to over-sleeve a G/Y core of a multicore cable, just at its ends, for use as a live conductor.

BS7671 does specifically forbid this in the case of a G/Y-insulated single cable. However, in terms of cores of multicore cables, all it says is that G/Y colours must not be used to 'identify' anything other than earth/CPC - but it also allows that any core can be 'identified' by over-sleeving just at the terminations, without making any exception of G/Y cores.

None of that makes it (IMO) any less 'orrible, even if compliant. Of course, the situation as a whole can only be compliant if there is a CPC feed to whatever is at the end of the cable (JB or whatever) via some other cable, since the regs require that every point in the installation be supplied with a CPC (even if it is not, currently.'needed').

Kind Regards, John

 

[sparkwright]

As I understand, and I apologise for any repitition of the above.

You cannot use the bare earth wire in a twin and earth cable as a live conductor.

You can use the green and yellow core in a flex as a live conductor if oversleeved the appropriate colour - though bad practice.

Every electrical fixed accessory should have an earth point (exception being plastic lampholder on a ceiling rose). With this in mind, the above paragraph is made all the more difficult, though the earth can easily be provided by another cable.

Please feel free to correct me.

Wait for it...

 

[EFLImpudence]

I would say that sums it up nicely.

Whilst not specifically banned it very rarely possible.

 

[JohnW2]

This does, indeed, seem like simple repetition of what I've just written, but ....

As I understand, and I apologise for any repitition of the above. .... You cannot use the bare earth wire in a twin and earth cable as a live conductor.

Agreed, for a whole host of reasons, as well as hopefully being 'obvious' to most sane people!

You can use the green and yellow core in a flex as a live conductor if oversleeved the appropriate colour - though bad practice.

Agreed.

Every electrical fixed accessory should have an earth point (exception being plastic lampholder on a ceiling rose).

Agreed.

With this in mind, the above paragraph is made all the more difficult, though the earth can easily be provided by another cable.

I'm not totally sure of your point. As I wrote before, I agree that one can theoretically 'get away' with an over-sleeved G/Y core IF there is a CPC supplied to the same place (that the 'over-sleeved cable' is going to) by some other cable.

Kind Regards, John

 

[RF Lighting]

Yep sparkwright has it spot on. I'll translate in to pluber lingo for you

Basically you can not wire a cylinder stat on a Y plan using 3 core flex, as using the green and yellow wire as a live / switched live would leave the cylinder stat without an earth. This is a contravention of the regs regardless of wether the stat actually requires an earth or not.

If you had a 3 channel programmer on an s plan plus system, you could run two 3 core flexes between the programmer and the wiring centre, with one flex carrying permanant live, neutral and earth and the other flex carrying the three switched lives, with the blue and green and yellow wires sleeved brown at all terminations. Whilst this is compliant with the regs, it's still a bodge, and not something that a competant installer ought to be doing.

 

[ericmark]

I agree with you John I was horrified to find one of the scheme operators tells it's members they can over sleeve green/yellow which I had always considered was a no.
514.4.2 is the regulation in question and to me the full stop means end of a statement so when it says:-
"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." I would have said this means no over sleeving. However the next sentence is. "Single-core cables that are coloured green-and-yellow throughout their length shall only be used as a protective conductor and shall not be over-marked at their terminations, except as permitted by Regulation 514.4.3." which seems to say if not single core then you can over mark at the termination.

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.

I personally think even if strictly to regulations you are permitted to over sleeve this is still very dangerous. We have all opened up ceiling roses where the brown or red over marking is missing and I am sure the same will happen if green and yellow is over sleeved it will fall off and will cause a danger and it very bad practice.

 

[sparkwright]

With this in mind, the above paragraph is made all the more difficult, though the earth can easily be provided by another cable.

I'm not totally sure of your point. As I wrote before, I agree that one can theoretically 'get away' with an over-sleeved G/Y core IF there is a CPC supplied to the same place (that the 'over-sleeved cable' is going to) by some other cable.

Kind Regards, John

An example could be a central heating programmer perhaps.

Fed by two 3 core flexes. One green and yellow going to the earth terminal. The other green and yellow used as a live conductor.

 

[RF Lighting]

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.

It's not insulated, it is SHEATHED, so it can not and must not be used for any other purpose other than earth.

 

[JohnW2]

I'm not totally sure of your point. As I wrote before, I agree that one can theoretically 'get away' with an over-sleeved G/Y core IF there is a CPC supplied to the same place (that the 'over-sleeved cable' is going to) by some other cable.

An example could be a central heating programmer perhaps. ... Fed by two 3 core flexes. One green and yellow going to the earth terminal. The other green and yellow used as a live conductor.

Sure, CH programmers/'wiring centres' are where one is most likely to encounter this sort of thing.

However, it's not necessarily as simple as you suggest. Where is that flex whose G/Y is being used as a live conductor going, and how does that place (wherever it's going to) get its required CPC? If it were going to another JB/wiring centre/whatever, then it might be possible, but of it were going to a CH component (pump, valve, boiler, stat etc.) it's pretty unlikely that any other cable would be taking a CPC to that component. So, yes, there will occasionally be situations where it could be done (compliantly), but only pretty rarely.

Kind Regards, John

 

[sparkwright]

I'm not totally sure of your point. As I wrote before, I agree that one can theoretically 'get away' with an over-sleeved G/Y core IF there is a CPC supplied to the same place (that the 'over-sleeved cable' is going to) by some other cable.

An example could be a central heating programmer perhaps. ... Fed by two 3 core flexes. One green and yellow going to the earth terminal. The other green and yellow used as a live conductor.

Sure, CH programmers/'wiring centres' are where one is most likely to encounter this sort of thing.

However, it's not necessarily as simple as you suggest. Where is that flex whose G/Y is being used as a live conductor going, and how does that place (wherever it's going to) get its required CPC? If it were going to another JB/wiring centre/whatever, then it might be possible, but of it were going to a CH component (pump, valve, boiler, stat etc.) it's pretty unlikely that any other cable would be taking a CPC to that component. So, yes, there will occasionally be situations where it could be done (compliantly), but only pretty rarely.

Kind Regards, John

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.