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

[JohnW2]

What a contrived argument! I do hope that nobody is mislead by your posting.

...Also, there is also the oft-quoted fact that at least one 'official body' (was it ESC? or NIC?) has given it's blessing to over-sleeving of G/Y cores in flex - so it's certainly not just me who might be 'misleading' people.

Found it! - it is NICEIC (if not also other bodies) who are also apparently "contriving arguments and misleading people" ... (click here)

Kind Regards, John

 

[mfarrow]

412.2.3.2 says "... a circuit supplying one or more items of Class II equipment shall have a CPC run to and terminated at each point in wiring and at each accessory" - so your double/reinforced insulation wiring centre therefore does require a CPC to be run to (and terminated within) it.

I see you missed out the first part of that regulation. It's not a discussion for here anyway.

However, if that requirement is satisfied by at least one cable entering it, that theoretically removes the need for CPCs in other cables going to the same place.

Unless using T&E in which case it would probably contravene 412.2.2.4 (unless something else subsequently allows it).

 

[EFLImpudence]

it is NICEIC (if not also other bodies) who are also apparently "contriving arguments and misleading people" ...

Yeah, but they are always doing it.

 

[JohnW2]

it is NICEIC (if not also other bodies) who are also apparently "contriving arguments and misleading people" ...

Yeah, but they are always doing it.

They are, and I never suggested that their word is to be regarded as 'gospel'. I was merely pointing out that I am far from the only person who has presented the interpretation of the regs (which you have agreed is logical) that was being described as a "contrived argument".

As I keep saying, I do not regard over-sleeving a G/Y core of a multi-core cable (or use as a live conductor) as being 'good practice' (far from it!), and I would really have expected (and would have welcomed) the regs to totally forbid it - but, unlike stillp, I just don't think that the words of BS 7671 actually do (forbid it).

Kind Regards, John

 

[EFLImpudence]

I was merely pointing out that I am far from the only person who has presented the interpretation of the regs (which you have agreed is logical)

Only in the contrived situation you have proposed.

I would really have expected (and would have welcomed) the regs to totally forbid it - but, unlike stillp, I just don't think that the words of BS 7671 actually do (forbid it).

Perhaps because of 411.3.1.1 & 412.2.3.2 they did not consider it necessary, unlike singles.

 

[mfarrow]

Perhaps because of 411.3.1.1 & 412.2.3.2 they did not consider it necessary, unlike singles.

Why are singles so special when considering what is apparently obvious to allow/disallow?

And what about class II installations covered by the exception?

What about multicore cables where the sheath/armour is being used as the CPC?

What about cables with more than one core marked as G/Y (I guess that would be a special order but hey it can exist!)?

 

[EFLImpudence]

Why are singles so special when considering what is apparently obvious to allow/disallow?

Presumably to stop them ever being used as live conductors - quite sensibly and understandably.

And what about class II installations covered by the exception?

If you mean 412.1.3, that is a somewhat unusual limited situation including supervision.

What about multicore cables where the sheath/armour is being used as the CPC?

What about them?

What about cables with more than one core marked as G/Y (I guess that would be a special order but hey it can exist!)?

If such had been obtained as a special order, why would it be used when not required?



So, you agree with John's logic but not his and other's good practice.

I do not understand your reference to 412.2.2.4

 

[JohnW2]

I was merely pointing out that I am far from the only person who has presented the interpretation of the regs (which you have agreed is logical)

Only in the contrived situation you have proposed.

I must be dim, since I really don't see what is 'contrived' about it. I am merely looking at what the words of the regs say. The regs tell us that G/Y colours may not be "used to identify" anything other than a protective conductor, but it is clear that they regard the colour of over-sleeving, not of the underlying insulation colour, as being the colour which is "used to identify" the conductor. Otherwise, as I implied in the near-rhetorical question I asked stillp (and which I'm not surprised has not received a reply), if one used a blue-insulated conductor over-sleeved with brown as an L conductor, the colour being "used to identify" that L conductor would be blue - which is clearly ridiculous.

I would really have expected (and would have welcomed) the regs to totally forbid it - but, unlike stillp, I just don't think that the words of BS 7671 actually do (forbid it).

Perhaps because of 411.3.1.1 & 412.2.3.2 they did not consider it necessary, unlike singles.

Maybe - but if that's the case, I would say that they didn't think carefully enough, because they did not consider the possibility that 'a point in the circuit, or accessory' can be supplied with a CPC by just one of two or more cables.

I personally don't think that 411.3.1.1 & 4.2.2.3.2 really go far enough. I would really have expected a simple explicit demand that every LV multi-core cable had a CPC, to give some extra protection in the case of cable penetration etc. (as well as 'in case it was subsequently needed).

Kind Regards, John

 

[JohnW2]

Perhaps because of 411.3.1.1 & 412.2.3.2 they did not consider it necessary, unlike singles.

Why are singles so special when considering what is apparently obvious to allow/disallow?

I think EFLI's point is that, if one doesn't think deeply enough about those regs (i.e. don't consider multiple cables going to the same place, or to the other situations you mention below), one may end up thinking that every cable must carry a CPC and hence there would never be any possibility to use the G/Y for any other purpose (with any standard cable which had only one G/Y core)

And what about class II installations covered by the exception?

I agree that 412.2.2.4 somewhat confuses the situation (and perhaps that should be made more clear), but there is no doubt what 411.3.1.1 & 412.2.3.2 are calling for.

What about multicore cables where the sheath/armour is being used as the CPC? ... What about cables with more than one core marked as G/Y (I guess that would be a special order but hey it can exist!)?

These are essentially the same, in that they could leave a 'spare' G/Y core, even if the cable is carrying a CPC - so, again, if their thinking was as EFLI has suggested, perhaps a further indication that they didn't think carefully enough about all possible situations.

As I've said, it would have been so easy for them to simply forbid the use of a G/Y conductor as anything other than a CPC in any situation, and I wish they had - since saying that in relation to only singles just causes all this discussion (usually initiated by plumbers!), which really didn't ought to be necessary.

Kind Regards, John