Wiring colour coding for double light switches

[Nigel Watts]

I would like to know (not for my benefit but on behalf of a friend who may possibly be legally qualified to do such things but may have forgotten - you understand I'm sure) what the correct colour coding is for a three core cable linking two switches which operate the same light.

Two of the wires have to go to the alternative positions on the two-way switch, and the third to the point from which they are switched. Standard three core cable is already in place (or so I understand from my friend), so it's only the second fix that remains to be done.

 

[Pford75]

I would suggest to your 'friend', that if he is properly qualified to do this work...he should know

Speaking as someone who got a shock from the dodgy electrical work of the previous owners....I really don't understand why your 'friend' doesn't get a professional. If he chooses not to, is he aware that his work should be certified by building control for Part P?

Sorry if this sounds officious, but I don't understand why we all compain when people flout planning laws (with respect to LBC), yet we happily ignore the bits of bulding control we don't like.....

 

[Nigel Watts]

You are right of course, but I take some comfort in the knowledge that my friend has a degree in engineering from one of our leading universities, and is quite a good handyman. I understand that he even does some lime plastering, furniture making and clock repair in his spare time.

 

[GK]

Since they're all live does it matter which colours are which?

I can't do a two way switch any more because instead of the colours being red, yellow and blue instead of as now, black, grey almost black, and brown almost black, I used to be able to tell them apart. I suppose this is what "harmonisation" means.

In the switch where the switch wires come in from the rose: Connect red of 2+e to the common, and blue and yellow to the other two switch terminals. Then the spare red of the 3+e goes to the black of the 2+e switch wire,using a single connector strip. This livens up the bulb, assuming you've done standard loop-in rose wiring.

At the two-way switch end, where you've just got 3+e: red to common, blue and yellow to other two.

I KNOW there's a way to do two-way switching without having a little connector strip in the box, but I CAN'T remember how to do it.

Since all colours are live you're (were) supposed to put a red sleeve on them all.

edit:
I always make sure a lamp is not on when ALL switches are in the off position. Just swap a blue and yellow if this isn't happening.

 

[thiambal]

The electrics forum on DIYNOT site has a number of standing posts expaining how to wire up pretty much every combination of lights and switches.

 

[Penners]

Nigel

Hopefully this will help your friend.

David

 

[Ushy M]

Nigel,

Have just consulted Mr M who is a qualified electrician, and the description given by GK is indeed the right approach (with a piece of terminal block) as that way you can tell what each bit of wire is doing. Hope this helps your friend.

 

[middi]

Lovely picture diagram Penners, my "friend" also was well impressed.

 

[Penners]

Yes Middi - I keep it handy for my friends, too. :wink:

 

[Nigel Watts]

My friend would like to pass on his thanks for the helpful advice. The lightswitch he is installing is a Forbes & Lomax "invisible" type - one which has a small toggle switch in a perspex plate behind which the wallpaper is visible. He wonders if anyone has experience of installing one of these in a wallpapered room.

 

[Penners]

Aren't we all lucky to have so many electricians as friends?

 

[biffvernon]

Friends are always useful when investigating things to do with planning and building regs.

My friend wants to know what the pretty green and yellow stripey wire does when it is just attached to the plastic box. She didn't have one in the old lighting circuit.

 

[monkey writer]

I also have a curious friend. This friend wants to install old bakelite round light switches in his house. He wonders how he should test them to ensure they are safe before installing them?

He understands that the wooden baseplates are no longer acceptable (or is that just for ceiling roses?) but are there any other original components that should be replaced before using?

 

[Penners]

My friend wants to know what the pretty green and yellow stripey wire does when it is just attached to the plastic box. She didn't have one in the old lighting circuit.

Tell your friend that the pretty wire is for earthing the plastic box. :roll:

 

[biffvernon]

Thanks Penners, I'll pass on that sound advice. And the wooden baseplates? They need earthing too, do they?

 

[GK]

What are you going to do with the earth conductor if you don't have a terminal to wrap it around?

My friend always told me that it's bad practise (or is it practice?) to cut off the earth conductor even when it's not apparently required.

 

[NT]

I also have a curious friend. This friend wants to install old bakelite round light switches in his house. He wonders how he should test them to ensure they are safe before installing them?

He understands that the wooden baseplates are no longer acceptable (or is that just for ceiling roses?) but are there any other original components that should be replaced before using?

Bakelite switches can be used, but only some can be used without any complication. The main safety Qs are:
1. does the toggle have a sprung snap action?
2. does the front unscrew without use of a tool, to reveal live bits?

If the answer to 1 is no, or to 2 is yes, then a little complicatoin is needed to ensure the wiring meets modern safety standards.

For 1 = no, these are a risk on mains circuits, as they can catch fire if left accidentally in the mid way arcing position.

For 2=yes, these are a risk on mains circuits, as kids can (and will) remove the covers and wait to see who tries to switch the lights on in the dark, getting a nasty shock.

For 2=yes, one solution is to fit a tiny screw on the underside of the front cover to prevent it unscrewing by hand.

For 1 = no, or for switches that are grossly unsafe for other reasons, the only properly safe option is to fit a miniature transformer and relay, so the old switch operates on eg 6v, and controls the relay that switches the lights. Its quite simple to do, you just need a bit of space behind the switch, ceiling rose, or wherever.

Finally its wise to clean the interior of old switches up before use. And really finally, cleaning the contacts up is sometimes needed.

Wooden baseplastes are fine if either
a) the switch is separated from the plate by a fireproof barrier, eg thermoplastic, and this may be retrofittable.
or b) the switch is used on low voltage

Any and every switch can be fitted safely IF this is followed. If a person really doesnt understand whats safe and what isnt, the relay method enables any switch of any kind to be used perfectly safely (even bare uninsulated switches).


NT

 

[middi]

Nice one NT, we can now tell all our electrician "friends" not to go to BQ and buy packs of shiny plastic new switches when they can safely modify and restore the originals.

The only person to get a shock from these will be the building control officer.

 

[Penners]

Well, believe it or not, I've had a shock from electricity that's travelled through wood.

In my first fixer-upper house, I unwittingly drove a nail through an electric cable while I was nailing down upstairs floorboards (although I didn't know at the time that I'd done it). Some weeks later I was plastering the downstairs ceiling between oak joists, and I got a shock from my steel float.

The electricity had travelled from the cable into the nail, from the nail through the oak joist, from the oak joist into the wet plaster and into my float.

 

[Pford75]

Be aware that Baelite produces dangerous dust when drilled/sanded - so you should take appropriate precautions.