Replacing rotary dimmer with touch dimmer wiring question

[dutts]

Hi,

I am trying to replace an old rotary dimmer with a new touch dimmer but the wiring in the old dimmer doesn't seem to match that suggested on the new instructions. The dimmer is controlling two lights. Into the back box I can see two three-core cables coming in (Red, Black and Green/Yellow) and a two core (Red and Black).

My old dimmer has L1, L2 and C, and is currently wired with the two red cores from the three-core cables into L1 and the red from the two core into C. Both green\yellows are joined in a single sleeve and screwed onto back of the back box.

My new dimmer has Load, Slave and Live.

Can anyone tell me how I should wire this up? The instructions say black/blue onto Load, Red onto Live but my setup is a little different.

Any help would be most appreciated.

Rich

 

[NewOrder]

Can't help with the wiring, but was the old dimmer a double? And the new one a single switch? It sounds like that could be the problem. Or did the old switch have one control (i.e one knob) to control both lights?

 

[bernardgreen]

Most probably the two reds in L1 are the looped live supply that loops round all the switches. The single red in C is the switched live going to the lamp.

Probably but not certain

Try the two reds in Live and the single red in Load.

 

[dutts]

Hi guys,

Thanks for your replies, just to clarify, there is one single dimmer switch controlling two lights.

I thought that the two 3 cores I can see coming into the switch would have come from the two lights but I guess that wouldn't make sense as that would leave a single two core unearthed cable coming in to feed live?


Rich

 

[Taylortwocities]

You can't.

I guess this is one of those fancy Varilight (or similar) touch dimmers.

They do not work with a dimmer at one end and a standard switch at the other. You'll need a slave dimmer at the other end and for your wiring to achieve the quirky way they like to be wired.

 

[dutts]

Sorry Taylortwocities, you've confused me a bit there.

The current set up is two ceiling lights controlled by a single wall dimmer switch (with just one rotary dimmer on).

I just want to replace the switch with a new touch one.

 

[Taylortwocities]

Ahh yes, Soory. I thought there was another switch.

Looks to me like Bernard has given you the solution..above.

 

[ban-all-sheds]

a two core (Red and Black).

That's not good at all - there should be an earth core in that cable.

My old dimmer has L1, L2 and C, and is currently wired with the two red cores from the three-core cables into L1 and the red from the two core into C. Both green\yellows are joined in a single sleeve and screwed onto back of the back box.

And the black cores... ?

 

[ban-all-sheds]

Most probably the two reds in L1 are the looped live supply that loops round all the switches. The single red in C is the switched live going to the lamp.

Probably but not certain

Try the two reds in Live and the single red in Load.

And the light gets its cpc from.... ?

 

[bernardgreen]

And the light gets its cpc from.... ?

May be it is old wiring and the lighting circuit was not installed with CPC ( earth wire ). Provided no metal lamps or switches are installed on the circuit the lack of CPC in a lighting circuit while regretable is not as bad as it appears to be under modern regulations.

 

[dutts]

a two core (Red and Black).

That's not good at all - there should be an earth core in that cable.

Let me check again when I get home this evening but I'm pretty sure there are only two cores in the green and yellow sleeve attached to the back box (and that they come from the two three cores). However at the ceiling rose end there are three cores coming out so I may be wrong at the switch end. Let me check.

My old dimmer has L1, L2 and C, and is currently wired with the two red cores from the three-core cables into L1 and the red from the two core into C. Both green\yellows are joined in a single sleeve and screwed onto back of the back box.

And the black cores... ?

Ah sorry, the black cores are all chocked together in the back box.

 

[ban-all-sheds]

However at the ceiling rose end there are three cores coming out so I may be wrong at the switch end.

Let's hope you are, because what you describe ("the black cores are all chocked together in the back box.") is a lighting circuit that loops through the switches, and AFAIK that was unheard of at the time lighting circuits were allowed to be unearthed.

So if the cable going to the light does not have its earth connected to the others at the switch then the light does not have an earth, and nor does the cable.

This is a Bad Thing.

 

[dutts]

Ok, well I hope I'm wrong too! Let me check when I get home.

So, if I am wrong and there are in fact 3 x three core cables going into the backbox with the following:

- all (x3) the blacks chocked together
- all (x3) the green/yellows attached to the back box
- 2 x red into L1 on the old dimmer
- 1 x red into C on the old dimmer

Is it possible to translate this to the Load, Slave and Live terminals on my new dimmer or am I onto a non-starter with this?

Rich

 

[ban-all-sheds]

As you don't have a slave dimmer, but you do have live cables coming in, and a cable going out to the load I would hope it's not too hard for you to DIY.