Wiring and their colours

[Grumps]

Hi All, Sorry about subject clarity. I've eventually got an urge to finish off the re-wiring of a 2nd home. All of the rings are in (first fix) and I'm thinking about the lights. Kitchen circuits (ring, lights, hob) were done professionally about 5 years ago. Yes, I have informed building regs/control and paid a fee. The hardest decision is that I'm trying to make as little mess as possible so redecorating is minimal. So far so good; only a few visible chases and I have some of the old wallpaper to repair this. But with the light switches, I'd like to replace the current wires with new T+E as there is currently no earth at the switches. I know there doesn't HAVE to be, but it's a nice to have. The house was first wired in the 60s and the lighting circuit is a "loop at switch" type. So each switch (presumably except the last) has 3 red wires; Line in, line out to next switch, and switched line to light fixture. These wires are stranded (I haven't counted, but probably 5 strands). Instead of chasing out and removing the old wires, can I re-use the existing 3 conductors and sheath one in yellow/green? I can access the wires in the ceiling void and loft where a junction box could be employed to "convert" to T+E going to the fitting. This would also be coupling red conductors to brown/blue. I have Brian Scaddan's 18th Ed IET wiring regs as a reference, but can't see anything that thwarts my plans. Ta for any comments.

[Jeff Layman]

Have you considered replacing the switches with Quinetic ones? No concerns about wiring (and no redecoration required), but some expense involved.

[Grumps]

Thanks. Yes, I had been pointed in that direction before. Apart from it's black magic and must be the devil's work, I think I want the option of using metal switches, so need to get an earth into the switch box.

[Animal]

No you can't use live coloured conductors for earth & vice versa. From a safety pov it's not hard to use 12v on the switches, just need a psu & relay. I forget what the regs say about that.

[Grumps]

Even if you sheath it in yellow/green? I could strip the insulation from one of the reds so it would look like a bare CPC.

So use the existing wiring at 12V. Are there specific colours for that?

[Mike Humphrey]

Are you sure that's the case? I know that overmarking green/yellow to any other colour isn't allowed, but as far as I'm aware the other direction is fine. It's commonly done with three-core SWA cable - you usually get brown, black, grey and want brown, blue, green/yellow, so re-mark the black and grey with tape. (Yes, I'm aware that single-phase coloured SWA exists - it's not as easy to find as the three-phase stuff).

Mike

[Andrew]

No need for an earth to the back box with Quinetic switches because there is no mains at the switch. And, metal switches are available. IIRC compatible with the Varilight range.

[Scott]

I don't think OP wants the devil as project manager :-)

[Scott]

But okay to reconfigure neutral to live (using brown or previously red) where there are two switches for the same light? This seems an artificial distinction.

[John Rumm]

I don't think that is actually true when talking about wires contained in a cable like T&E.

It *is* true for singles in conduit where a wire identified with green/yellow sheath can't be over marked for another purpose. (since the risk of confusion with other wires of the same colours would be very high)

So you can over mark another colour wire as an earth, so long as you do it at both ends of the cable.

[Grumps]

Thanks. That's what I was hoping. So I can take one of my red wires and over mark it green/yellow.

What're the panel's views on using stranded cables? There are a few strands in each wire, not like flex, maybe only 5 or so strands.

[Andy Burns]

Some parts of my house had/have multi-strand (not fine stranded like flex) T&E, is yours T&E or individual singles? I think 3x0.029" strand is rough equiv of

1.5mm^2 and 7x0.029" is rough equiv of 2.5mm^2

[John Rumm]

Some T&E is stranded. These days it tends to only be the larger CSAs (6mm^2 and over), but historically even 2.5mm^2 was available in stranded.

(and imperial T&E was also often stranded, and 7/.029" looks pretty similar to 2.5mm^2)

[Robin]

I thought I'd just check that your cable is copper since all the lighting circuits here were wired in stranded aluminium cable at some time in the sixties:

[Grumps]

Mine is individual singles, not T&E. I'll have to count the strands when I'm at the house again.

[John Rumm]

You can get some metal clad switched that are also double insulated. So those could be used on a circuit without earthing.

[Grumps]

How does one tell if it's aluminium, CCA, or copper? Does CCA and copper look the same?

I'm pretty sure some of the cabling is/was aluminium as one of my neighbours said that their electrician told them this. No reason not to assume that my house isn't the same. Would there be specific circuits that were aluminium in the 60-70s? Lights, rings?

[Grumps]

Thanks. So now I have options. a) Over-mark one of the wires as earth and then ANY metal clad switch will be OK. b) Forget the earth (but I do have three wires present) and use double-insulated metal clad.

But now (in another thread) I need to ensure they're copper.

[Andy Burns]

Not after you scrape it with a stanley knife.

[Mike Humphrey]

If you're re-wiring, then option b isn't compliant with the regs, as an earth must be provided even if it's not used. It will be perfectly safe, of course, with a plastic or double-insulated switch - the issue is if it gets replaced later.

Option a would I think not be considered best practice, but does comply with the letter of the regulations. Ideally you use a cable that's the right colour to begin with, but overmarking is permitted as long as it's not *from* green/yellow to another colour. You also should mark the other two reds with brown tape, as the old colours aren't allowed on new work.

The gold standard would be to either replace the cable with new T&E, or use a non-mains switch.

Mike