2 gang light switch mystery

[samwise]

Hi, any help on the following would be greatly appreciated...

My lounge has two lights in it. It currently has a 2-gang switch, but one switch turns both lights on and off. The other does nothing (as far as I can tell!)

I have bought a dimmer to replace the current switch. Since only 1 switch does anything, I bought a single dimmer to connect to both lights.

Four cables come into the box. All four earths are earthed, all four black cables are connected together. The four reds are connected to the light switch. 2 cables go into the '1 Way A', and 2 cables go into '1 Way B', and the two Coms are connected together with a seperate length of wire

I assume that to replace this with my single dimmer, I connect one pair of reds to the live of the new switch, and one pair to the load side. Is this correct, and will it matter which way round I do it?

Many thanks!
Sam

 

[Steve]

What terminals are on the back of that switch? can you post a photo of it? we need to see exactly what cables are connected to which terminals.

 

[superspark]

you can connect it like that, it doesn't really matter which way round the wires go but it is normal practice to connect live cables to com and s/l to L1.

don't forget to connect earth to faceplate if metal.

p.s. have you checked the rating of the dimmer.

 

[Lectrician]

Sounds as if you have a wall light cable hanging around somewhere....possibly live? Hopefully isolated safely.

The way the switch is wired doesn't sound correct.

The two coms are just linked together? No other cable in these terminals? So both switches would operate the same light. Are you sure this is correct?

 

[samwise]

Hi,

I had another look, and it appears I did get it slightly wrong - sorry!

To clarify:

2 reds come into 1 Way A
1 red comes into Com B (which is on the same side of the switch as 1 Way A)
Another independent red connects Com B and Com A
1 red goes into 1 way B.

I've taken a photo, but haven't had much luck posting it!

Sam[/img]

 

[Steve]

the 1 red into "1 way b" needs to be terminated in a terminal block behind the switch - as apparently it doesn't do anything. Connect the other 1 red from COM to the new switch COM, and the other 2 reds from "1 way a" into L1. This should work.

 

[Lectrician]

Should also terminate the neutral safely aswell......

 

[samwise]

Thanks - so I should terminate that one red with the other neutrals?

Can you think of a reason why the wire would be there if it doesn't do anything - could it be in another part of the circuit?

 

[andy]

Thanks - so I should terminate that one red with the other neutrals?

Can you think of a reason why the wire would be there if it doesn't do anything - could it be in another part of the circuit?

it could have been from a wall light, or a second ceiling light

 

[Steve]

Thanks - so I should terminate that one red with the other neutrals?

NO!

terminate it by itself in a seperate terminal block. dont connect to the neutrals!!!!

 

[Lectrician]

And take the neutral that is paired to that red out of the neutrals.

 

[samwise]

Cheers. Having thought about that one, I realised that would be a bit stupid! Fair point about isolating the neutral from that cable as well.

Thanks for your help.

 

[samwise]

And so the mystery goes on...

So, I did as was suggested - I removed and isolated the red that went into 1 way B, and isolated the neutral from that cable as well. Low and behold the switch doesn't work!

Checking I hadn't done anything stupid, I replaced the cables as before, and the lights are once again working fine. Pretty much ready to give up with this one and take my dimmer switch back!

Any ideas why there seem to be two lights in my lounge, but 3 lives that appear integral to the circuit???

Thanks

 

[danlightbulb]

It might be the 2 reds in 1 way A that are redundant. The common link is feeding the true light in 1 way B (with the 2 ceiling lights linked elsewhere).

Try isolating Way A wires, ditching the common interlink and using Way B as the output from the dimmer.