Twin brown and earth - can one core be marked blue for neutral?

[craig1234]

I'm currently building an extension (done under building regs including the electrical) and I've inadvertently run a couple of twin and earth cables each with two brown cores. One to an extractor fan and one to an outside socket. I've no idea where this drum came from as I've never knowingly purchased this type of cable. Unfortunately, I didn't realise that I'd used the wrong cable until I'd plastered so don't really want to remove it.
My question is, can I mark one of the cores as neutral in a similar fashion to marking a blue core live in a lighting circuit?

 

[Harry Bloomfield]

My question is, can I mark one of the cores as neutral in a similar fashion to marking a blue core live in a lighting circuit?

Yes, fit some blue over sleeving, at each termination.

 

[craig1234]

Thanks Harry - pleased to hear that!

 

[Ivor Windybottom]

I'd suggest that your misuse of cable in this way is very undesirable. You'd need to test to know which is Line at each end and it would be very easy to get this wrong, either now or in future if appliances are replaced. The result could be that a light fitting remains at 230V whilst off, or a socket remains live while switched off, among other risks.

The intended use of this cable is from a light fitting to a switch. One is permanent live, the other switched live. In this case it doesn't matter which is which.

This being its intended purpose, it's likely to be 1mm or 1.5mm. So check this and its suitability for the intended purpose.

It will cost you perhaps £30 or so to do it properly. A scrap metal merchant would pay you for your drum of cable if you really have no purpose for it. I regularly make trips to our local scrappie with offcuts of new and old cable and usually come away with somewhere around £100 for a load of old rubbish.

But the fact you've plastered it in probably will result in you leaving it. So make bloody sure you know which is which by continuity testing from end to end.

 

[Adam_151]

No problem oversleeving as long as you have correctly belled out which core is which, however as others have said, I'd be concerned about the outside socket, as I've never seen twin brown 2.5mm and theres probably little reason for it to exist, so I'm guessing its probably 1.5mm², now that could be ok if its from the load side of a fused spur, but as part of the ring its no good

 

[craig1234]

Thanks for the replies.
One of the cables (they are 1.5mm) feeds from a switched spur to the extractor fan so this can be protected by a 3A fuse which I understand is acceptable.
My original intention was that the external socket (which has two of the 1.5mm brown/brown cables feeding into/out of it) would be the last socket on the ring. However, I am now thinking that the ring should terminate at the socket before and that I treat the external socket as a spur doubling up the cores feeding to the socket. I know this is not very "elegant" but any problems in doing it this way?
With regards to identifying the two brown cores, they are a slightly different shades but I will "bell" them out anyway.

 

[Harry Bloomfield]

However, I am now thinking that the ring should terminate at the socket before and that I treat the external socket as a spur doubling up the cores feeding to the socket. I know this is not very "elegant" but any problems in doing it this way?

The spur before the socket, is mandatory if using 1.5mm, and worthwhile making it a double-pole isolated spur. That will ensure the socket outdoors, can be completely isolated should a fault occur, as is common with outdoor sockets. It would also be essential that it is protected by an RCD, which is another good reason for the double-pole isolator.

 

[JohnW2]

I'd suggest that your misuse of cable in this way is very undesirable. You'd need to test to know which is Line at each end and it would be very easy to get this wrong, either now or in future if appliances are replaced. The result could be that a light fitting remains at 230V whilst off, or a socket remains live while switched off, among other risks.

Yes, but that risk exists at present, due to the absence of any identification of the neutral.

If replacing the cable is impractical/inconvenient. then I would say that the sensible/safe course is surely for the OP to identify now (by testing or whatever) which is the neutral at each of the ends of the cables concerned, and then to identify those ends with blue oversleeving, Isn't it?

If anyone subsequently does something wrong as a result of failing to pay any attention to the oversleeving, then I would say that such was 'their problem' - it's not, after all, as if oversleeving is non-conformant or non-compliant with BS7671.

Kind Regards, John

 

[Harry Bloomfield]

The electrons care little, or not at all, what the colour of the plastic insulation is -the colour is simply for identification by the installer, and those who might follow.

 

[JohnW2]

The electrons care little, or not at all, what the colour of the plastic insulation is -the colour is simply for identification by the installer, and those who might follow.

Quite so - but it clearly is desirable that,for 'those who might follow', conductors are identified (in whatever way) to at least some extent.

Given that it is myself who is most likely to be the person who 'follows', at least for the foreseeable future, I do try to go a bit further than is required by regs, by including some 'functional identification' - i.e. to enable one to identify the permanent live in a feed to a switch which is wired with 'twin brown' (or 'twin red') or blue+brown (or black+red) with the blue (or black) over-sleeeved.

Kind Regards, John

 

[EFLImpudence]

Labelling is also an acceptable method of identification so one could write as much and in as many languages as one wanted just to be on the safe side..

 

[JohnW2]

Labelling is also an acceptable method of identification so one could write as much and in as many languages as one wanted just to be on the safe side..

Indeed. The only requirement is for 'identification' (just as L, N or 'protective conductor') and there are many ways in which that can be acceptably achieved.

I have established my own convention for identifying P/L inductors (in the presence of S/L ones) - and, although that is primarily for my own benefit (and, without explanation, would mean nothing to anyone else), it is described in the documentation which accompanies my installation.

Kind Regards, John

 

[mattylad]

If you oversleeve it, make sure the sleeve cannot fall off if the wire is undone.

 

[JohnW2]

If you oversleeve it, make sure the sleeve cannot fall off if the wire is undone.

Indeed. For than reason I always try to over-sleeve with (shrunk!) heatshrink.

Kind Regards, John

 

[sparkwright]

I'd suggest that your misuse of cable in this way is very undesirable. You'd need to test to know which is Line at each end and it would be very easy to get this wrong, either now or in future if appliances are replaced. The result could be that a light fitting remains at 230V whilst off, or a socket remains live while switched off, among other risks.

The intended use of this cable is from a light fitting to a switch. One is permanent live, the other switched live. In this case it doesn't matter which is which.

This being its intended purpose, it's likely to be 1mm or 1.5mm. So check this and its suitability for the intended purpose.

It will cost you perhaps £30 or so to do it properly. A scrap metal merchant would pay you for your drum of cable if you really have no purpose for it. I regularly make trips to our local scrappie with offcuts of new and old cable and usually come away with somewhere around £100 for a load of old rubbish.

But the fact you've plastered it in probably will result in you leaving it. So make bloody sure you know which is which by continuity testing from end to end.

Not really any different to using brown and blue cable for a switch drop when you have to put brown sleeving over the blue.

Not really any different to multicore flex or swa where the cores ate all the same colour, but do have numbers printed on them.

It's inconvenient, definitely will give the next man something to think about, but I seem to recall pyro would have black sleeves on each conductor, and that had to belled out, and then the live wire was (nearly always) identified with a piece of red sleeve or similar.

If it doesn't break any rules, and it's not easy to replace, then it's going to stay that way - I would imagine.