Well, it is clearly a non compliance against current regs. It may well have been allowed when it went in,though - for quite a while concentric cables were permitted.

Is it a dangerous non-compliance ?  probably not, especially if the cable route is either obvious or mostly in the 'landlords area' where random tenants should not be hanging pictures anyway.  And in practice assuming neutral is the outer, then any nail accidents will result in power going off smartly. We'd not worry if it was a network operator's cable after all.

If it is too accessible at the ends where it is single insulated, can things be sleeved or 'wizards hatted' or protected with mini-trunking or similar ?

Mike.

I agree.  One point to watch though if you are replacing whatever is on the end is that the terminal that receives the solid Al core needs to have been designed with that in mind.  I dont have the standards to hand but I would definately check before terminating it in anything different to the original.  DNO terminals for this sort of thing are mostly relatively heavy copper blocks with multiple screws which are tightened to required torque.  I doubt that you would get a decent connection with any longevity with a cage type terminal.

Thank you both for the good advice.

It would probably be fine for continued use in practice. Seems to NON compliant with regulations though.

All live conductors are now required to be insulated and sheathed. In concentric cable as described the neutral is merely enclosed in the outer sheath and is not insulated

I suppose you could declare it a PEN rather than N and comply with BS 7671 (section 543.4) - although you'd probably want to avoid DP switching upstream, and of course deem it to be part of the BNO's installation rather than the consumer's to meet the ESQCR. But again puts it in context as far as actual safety is concerned.

   - Andy.

AJJewsbury said:

I suppose you could declare it a PEN rather than N and comply with BS 7671 (section 543.4) -

I did think about this (it being in the BNO network), but the provision of earthing alongside it made me think again (you can't have PEN downstream of the PEN-PE split in BS 7671, or IEC 60364 for that matter).

But, if the 16 sq mm is bonding (not cpc) ... ??? Without seeing the installation, at this point, we'd be guessing?

So if you use semantics to make it comply, does that make it safe? 

lyledunn said:

So if you use semantics to make it comply, does that make it safe? 

I know the above is perhaps a divisive question ... and I do see the point ... but 'comply' with what exactly?

In terms of ESQCR, all that needs to be established is whether the wiring is the responsibility of a Consumer or not. That might rest on where the meters are ... or not ... but without knowing a little more about the installation, this one's tricky.

BS 7671 on the other hand does not prohibit PEN conductors. It does, however, prohibit re-combining N and PE after you've split them. So, we'd have to establish whether that has happened before saying it doesn't conform to BS 7671 ?

So, I don't think it's so much 'semantics' I was playing with, but trying to get an understanding of the arrangement to see if we could establish a better-informed opinion ?

It's safer than T and E sub-mains that would probably be a "C3"- the live is surrounded by neutral, and as neutral is within  a volt or two of earth in a TNCS system, it is almost as safe as a correctly earthed SWA - we need two faults, the mis placed nail and an open circuit neutral to make it immediately dangerous.
SWA is very similar.

What we are doing is choosing the right bit of the right regs to apply, to recognize that level of safety.

More generally:-
Complying with all or any regs is not on its own a guarantee of safety in all cases - some sense is required.

Non-compliance is not a guarantee of danger, but needs more thought before deciding if something is OK or not.

in short, BS7671 is neither always sufficient, nor always necessary..... but in most cases of course it is ;-)
Mike.

I would argue that it was safe anyway, but that careful use of semantics could perhaps be justified as a way to prove that safety.