I have to re-wire a light switch due to the cable not quite being long enough. The house was built in the early 70s and the switch currently has two strands of red/green to it. This is a straight forward replacement so a junction box in the loft and a new bit of cable is all that needed - there's not much thought invloved. I have some 1mm twin and earth (blue and brown). Is that OK for this? I remember reading somewhere that the core colours should both be red. If so, where do I get 1mm twin and earth with both the cores red? B&Q/Screwfix don't seem to list such a thing!
rewiring light switch: cable core colour?
- Thread starter BonfireMan
- Start date
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If it's got red/green cable, then that's got to be quite old - so I don't think it's as straight forward a replacement as you think. If nothing else, if the new cable you are putting in is going to be buried at less than 50mm in the wall, and not in earthed metal conduit (or of a suitable type such as SWA), then you need RCD protection on it, which I doubt you have at the moment...
Also, does the existing cable have a CPC (earth conductor), if not then how are you going to provide an earth to the back box for the light switch etc?
You can get T&E with two brown cores (colours used to be red/black, now it's brown/blue, so the two reds are now two browns), but it's not an essential requirement. You can use brown/blue, just put a bit of brown sleeving/tape over the blue core at both ends to indicate it's a switched live...
Also, does the existing cable have a CPC (earth conductor), if not then how are you going to provide an earth to the back box for the light switch etc?
You can get T&E with two brown cores (colours used to be red/black, now it's brown/blue, so the two reds are now two browns), but it's not an essential requirement. You can use brown/blue, just put a bit of brown sleeving/tape over the blue core at both ends to indicate it's a switched live...
That's something you need to rectify....
The house is no older than 1970 so it's not that old! The cable will be down the centre of a stud wall and I'm planning to put some of that oval conduit round it for good measure. It is already on an RCD - the consumer unit was changed about ten years ago - so I don't *need* it?
The cables are two red/green; so there's two red *and* two green. That's two earths to choose from for the switch's back box.
Duh. Yeah - two browns. of course! Silly me. So I can get some 1mm cable with twin brown cores or some brown sleeve for the cable I already have?
Off to B&Q then. I need some plasterboard anyway...
The cables are two red/green; so there's two red *and* two green. That's two earths to choose from for the switch's back box.
Duh. Yeah - two browns. of course! Silly me. So I can get some 1mm cable with twin brown cores or some brown sleeve for the cable I already have?
Off to B&Q then. I need some plasterboard anyway...
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By green do you mean green/yellow sleeving, as that would make more sense. I can't see why there would be two of them however, as with T&E you should have two conductors (which could both be red/brown, or one red/brown, the other black/blue), and an unsheathed CPC (earth conductor).
Are you sure it had RCDs put in 10 years ago, and not just MCBs - the usual clue is as to whether there is a test button anywhere as opposed to just a lever...
Are you sure it had RCDs put in 10 years ago, and not just MCBs - the usual clue is as to whether there is a test button anywhere as opposed to just a lever...
Gosh. Makes the house about 39 years old. That does *seem* old. It's depressing as I'm not much younger... 
ban-all-sheds: heh-heh. funny.
ban-all-sheds: heh-heh. funny.
No, not green/yellow sleeving. The cable they've use just seems to always have an earth with it.
Here are the cables (should be vertical):
And here is the consumer unit:
I think half the unit is RCD but not the half the lights are on (which is the left half).[/img]
Here are the cables (should be vertical):
And here is the consumer unit:
I think half the unit is RCD but not the half the lights are on (which is the left half).[/img]
OK, assuming those aren't double insulated singles (i.e. have two layers of insulation between the outside air and the copper), then that installation is breaking the wiring regulations.
Given that, I would strongly recommend you get an electrician in to do a PIR (Periodic Inspection Report), and determine what else is wrong - otherwise you might be effectively sitting on a ticking timebomb...
Given that, I would strongly recommend you get an electrician in to do a PIR (Periodic Inspection Report), and determine what else is wrong - otherwise you might be effectively sitting on a ticking timebomb...
Just checked. Yeah, it is double insulated cable.
The house is ex-council so I doubt there's anything too dodgy about the wiring. It's just out of date. And untidy: this bit I'm tweaking was down the inside of a void in the stud wall, that had a duct for hot air central heating in it - the cable is just hanging loose - which is why it's too short to get the cable inside the stud now I've reclaimed the space back.
So I can continue as planned with no obvious issues?
The house is ex-council so I doubt there's anything too dodgy about the wiring. It's just out of date. And untidy: this bit I'm tweaking was down the inside of a void in the stud wall, that had a duct for hot air central heating in it - the cable is just hanging loose - which is why it's too short to get the cable inside the stud now I've reclaimed the space back.
So I can continue as planned with no obvious issues?
10 years ago nobody would have put lighting on an RCD circuit.
And look - they didn't with yours.....
They put a socket circuit on the non-RCD side too - hope they aren't on the ground floor....
So the reds go to the switch terminals and the greens to the earth terminal?
Make sure you connect them both.
You can, but I doubt the sheds will stock it.
That'll do. You should also then put a sticker on the CU to warn of the used of mixed colour wiring.
DI 1/1.5mm² singles? How odd....
No - there's the obvious issue of the circuit not being RCD protected...
What a fabulous reply, thanks.
No, both green cables are wired to the switch's back box. I will connect them both, of course!
I often wondered about those sockets not being on the RCD side. I had a new ring put in round the kitchen - there was only one socket before. Tsk, what did I pay my money for? So I think I should *already* have one of those stickers. Is it any wonder I've started doing some of these jobs myself? Where can I get a sticker? Can I make one?
So, swap the sides for the heating and the sockets, and put both lighting circuits on the RCD side? (A job for someone else, I'm not touching the fuse box - I'm not mad you know.)
I'm glad I made you laugh. I don't exactly trust my house either - I've always suspected everything but never quite found anything dodgy. The house is put together with rusty nails though...
No, both green cables are wired to the switch's back box. I will connect them both, of course!
I often wondered about those sockets not being on the RCD side. I had a new ring put in round the kitchen - there was only one socket before. Tsk, what did I pay my money for? So I think I should *already* have one of those stickers. Is it any wonder I've started doing some of these jobs myself? Where can I get a sticker? Can I make one?
So, swap the sides for the heating and the sockets, and put both lighting circuits on the RCD side? (A job for someone else, I'm not touching the fuse box - I'm not mad you know.)
I'm glad I made you laugh. I don't exactly trust my house either - I've always suspected everything but never quite found anything dodgy. The house is put together with rusty nails though...
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