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

[JohnW2]

Well yes - surely nobody would consider splitting LV between the 2 cables?

Indeed, that would be a bit daft, even though probably 'not a problem' in reality!

On a wider, digression sort of thing, if the application required two ELV pairs, then given that 411.3.1.1 has been satisfied by the cpc in the LV cable, what would the panel think about using the bare core in the other cable for ELV?

Well, in context, again daft - if one has three insulated conductors to choose from, and only needs two, why use a bare one?! However, more generally, as for the question as to whether a bare (but sheathed) conductor is acceptable (regs-wise) as a live conductor for ELV, I'd have to read the regs to see what they say. In terms of 'electrical common sense', it would clearly be fine.

Kind Regards, John

 

[ban-all-sheds]

Well, in context, again daft - if one has three insulated conductors to choose from, and only needs two, why use a bare one?!

On a wider, digression sort of thing, if the application required two ELV pairs...

 

[JohnW2]

Eric, Sorry but your logic is somewhat screwed. ... A regulation relating specifically to single core cables does not imply you can do what you like with multicore

We've been through this many times before, and I think eric is right.

In general, the regs are happy with use of any conductor for any purpose provided it is acceptably 'identified' - and over-sleeving just at the ends is one of the acceptable ways of doing that 'identifying'. Hence, in general, the regs allow a G/Y-insulated conductor to be used as a live conductor, provided there is appropriate over-sleeved at the ends.

However, the reg to which eric referred specifically forbids the use of a G/Y insulated single cable as anything other than a protective conductor. Hence, as eric says, that reg indicates that the only case in which over-sleeving a G/Y is not acceptable is if it is a single - hence, by logical implication, indicating that such over-sleeving is acceptable for multicore cables.

The main point is that many people seem to misread 514.4.2 to be generally forbidding the over-sleeving of G/Y for use as a live conductor in any situation, not just for singles.

Kind FRegards, John

 

[JohnW2]

Well, in context, again daft - if one has three insulated conductors to choose from, and only needs two, why use a bare one?!

On a wider, digression sort of thing, if the application required two ELV pairs...

Ah!

In that case, as I said, fine in terms of electrical common sense (regs would probably require over-sleeving, or something, at ends to 'identify') but I'd have to read the regs to see if it's actually allowed. I suppose an extension to your questions is whether single-insulated singles are acceptable for ELV. Again, I'd need to read to ascertain what the regs have to say about that - although, again, there is clearly no electrical safety issue.

Kind Regards, John

 

[bernardgreen]

It has been said a few times but no harm in repeating it.

If someone does any work on installed cables they will almost always assume the bare copper in the cables is the earth wire.

The risk of someone making that assumption and connecting the earth terminal of a metal lamp or other appliance to a wire which can become Live is too high to ever justify the use of the bare copper conductor as a Live conductor.

 

[JohnW2]

It has been said a few times but no harm in repeating it. If someone does any work on installed cables they will almost always assume the bare copper in the cables is the earth wire.

They will - but so will they with a G/Y-insulated conductor. In both cases, that can be largely addressed by 'identifying' the use of the core (probably by sleeving) at the ends. There is always the argument that someone may 'break into' a cable along its length and hence not see those identifications - but that must be a very rare occurrence (and would equally apply to a black or blue being used as a switched live, but 'identified' as such only at the ends).

Using a bare CPC as a live conductor is clearly totally unacceptable at LV, and even at ELV cannot be regarded as good practice. However, in the latter case, any theoretical hazards are likely to be minimal in practice, which is why I'll be interested to see what the regs have to say about it. Of course, in reality, T+E or 3C+E (with a bare CPC) is probably only rarely used for ELV, anyway.

Kind Regards, John

 

[mfarrow]

I believe the product standard for T&E specifies the bare conductor as a CPC only.

Yellow/green cores properly identified can be what you want inside a cable. Unless you're an idiot, you don't chop a cable or start splicing into it without confirming it's dead first at the other end, at which time the ID of the cores should be apparent.

 

[JohnW2]

I believe the product standard for T&E specifies the bare conductor as a CPC only.

I can well believe that - but the standard presumably wasn't written with ELV use in mind.

Yellow/green cores properly identified can be what you want inside a cable. Unless you're an idiot, you don't chop a cable or start splicing into it without confirming it's dead first at the other end, at which time the ID of the cores should be apparent.

Quite so. As I said, anyone chopping blindly into the middle of a cable (hopefully an extremely rare occurrence) is not only mad, but is also going to get caught out by black/blue used as line conductors etc., and goodness knows how they would interpret the colours of 3C+E!

Kind Regards, John

 

[ban-all-sheds]

I believe the product standard for T&E specifies the bare conductor as a CPC only.

Indeed.

But what if one of the two cores in an ELV circuit is grounded?

Yellow/green cores properly identified can be what you want inside a cable. Unless you're an idiot, you don't chop a cable or start splicing into it without confirming it's dead first at the other end, at which time the ID of the cores should be apparent.

There is no current or foreseen shortage of idiots.

 

[ban-all-sheds]

In general, the regs are happy with use of any conductor for any purpose provided it is acceptably 'identified' - and over-sleeving just at the ends is one of the acceptable ways of doing that 'identifying'. Hence, in general, the regs allow a G/Y-insulated conductor to be used as a live conductor, provided there is appropriate over-sleeved at the ends.

And vice-versa.

But I'm about to come to "allow".

However, the reg to which eric referred specifically forbids the use of a G/Y insulated single cable as anything other than a protective conductor. Hence, as eric says, that reg indicates that the only case in which over-sleeving a G/Y is not acceptable is if it is a single - hence, by logical implication, indicating that such over-sleeving is acceptable for multicore cables.

There's a lot of implying/inferring/extending going on there.

The main point is that many people seem to misread 514.4.2 to be generally forbidding the over-sleeving of G/Y for use as a live conductor in any situation, not just for singles.

With multicore cables it may not be explicitly forbidden, but does that automatically mean it must be good practice?


You could use the armour of this for the cpc, and use all 3 cores as live conductors

But should you?

 

[JohnW2]

I believe the product standard for T&E specifies the bare conductor as a CPC only.

Indeed. ... But what if one of the two cores in an ELV circuit is grounded?

I started wondering about that. However, if, even with ELV, a bare conductor can only be used as a "CPC", is not that defined as a conductor which only carries current under fault conditions, and not under normal operating conditions?

Yellow/green cores properly identified can be what you want inside a cable. Unless you're an idiot, you don't chop a cable or start splicing into it without confirming it's dead first at the other end, at which time the ID of the cores should be apparent.

There is no current or foreseen shortage of idiots.

Indeed not - but, as I said, such idiots would have the same problem with a black/blue being used as a line conductor just as much as if a G/Y were used as a line conductor - so the only way of protecting them from their own idiocy would be to ban anything from being a line conductor if it was not identified as such along its full length.

Kind Regards, John

 

[JohnW2]

However, the reg to which eric referred specifically forbids the use of a G/Y insulated single cable as anything other than a protective conductor. Hence, as eric says, that reg indicates that the only case in which over-sleeving a G/Y is not acceptable is if it is a single - hence, by logical implication, indicating that such over-sleeving is acceptable for multicore cables.

There's a lot of implying/inferring/extending going on there.

I wouldn't personally have said so - it comes just after the reg which effectively says that, in general, any conductor (whatever its native insulation colour) can be used for any purpose provided that it is appropriately identified (sleeving at the ends being one acceptable form of identification). 514.4.2 then indicates one exception to that general rule, by forbidding a G/Y single from being used as anything but a protective conductor. There doesn't seem to me to be much "implying, inferring or extending" involved in that.

With multicore cables it may not be explicitly forbidden, but does that automatically mean it must be good practice?

On the contrary, I think that most of us regard it as not being good practice.

You could use the armour of this for the cpc, and use all 3 cores as live conductors <pic of 3-core SWA>But should you?

As above, not good practice, but 'allowed'.

As I've just written in another post, I wonder if we may be a bit over-obsessed with the 'specialness' of G/Y - logically, we might be just as unhappy with using the blue of that SWA as a line conductor (since both G/Y and blue are normally 'expected' to be close to earth potential) but, in some situations (e.g. if it were going to an outdoor light switch), we would 'happily' do that (with over-sleeving at the ends).

Kind Regards, John

 

[Jackrae]

Eric, Sorry but your logic is somewhat screwed. ... A regulation relating specifically to single core cables does not imply you can do what you like with multicore

We've been through this many times before, and I think eric is right.

In general, the regs are happy with use of any conductor for any purpose provided it is acceptably 'identified' - and over-sleeving just at the ends is one of the acceptable ways of doing that 'identifying'. Hence, in general, the regs allow a G/Y-insulated conductor to be used as a live conductor, provided there is appropriate over-sleeved at the ends.

However, the reg to which eric referred specifically forbids the use of a G/Y insulated single cable as anything other than a protective conductor. Hence, as eric says, that reg indicates that the only case in which over-sleeving a G/Y is not acceptable is if it is a single - hence, by logical implication, indicating that such over-sleeving is acceptable for multicore cables.

The main point is that many people seem to misread 514.4.2 to be generally forbidding the over-sleeving of G/Y for use as a live conductor in any situation, not just for singles.

Kind FRegards, John

I accept that the conclusion may be correct as a statement of fact (you can use the "earth" wire as a power conductor in a multicore - it's just that the logic of getting there was wrong.

 

[JohnW2]

I accept that the conclusion may be correct as a statement of fact (you can use the "earth" wire as a power conductor in a multicore - it's just that the logic of getting there was wrong.

Fair enough. However, as I've just written to BAS, I personally find it pretty logical. First we have a reg which say that (amongst other things), in general it is acceptable to over-sleeve a G/Y to use it as a live conductor. That is quickly followed by a reg saying athat a G/Y single cannot be used as anything other than a protective conductor. I personally feel that it follows very logical to conclude that the second of those regs modulates the first, such as to indicate that using an (over-sleeved) G/Y as a live conductor is only acceptable for multi-core cables. That's how I see it, anyway - but I suppose I should really leave eric to defend himself

Kind Regards, John

 

[mfarrow]

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.