Replacing 2 way switch with simple dimmer

[sock99]

Hi there,

I have 2 two way switches connected to a ceiling light.

Can I just replace one of the switches with the dimmer (which only has two sockets) and just close off the third wire. Will the result be that the two way switch becomes the master on/off switch & the dimmer will do nothing until the two way switch is switched on? Is it safe?

Also, does it matter which 2 way switch I replace with the dimmer?

Thanks in advance for your help
Chris

 

[jj4091]

Sounds like you have bought a 1 way dimmer, what make is it?

 

[sparkyspike]

To be honest, you should change your dimmer to one with 3 terminals. If you don't want to, then which cables you use and which ones terminate depends on how the light is wired up. Can you clarify what cables you have at the light, and at each switch?

 

[sock99]

Sounds like you have bought a 1 way dimmer, what make is it?

It's Legrand (in France) and they are so expensive that I bought the cheapest of a reputable brand (£eighteen) which it turns out is a 1 way dimmer.

 

[sock99]

To be honest, you should change your dimmer to one with 3 terminals. If you don't want to, then which cables you use and which ones terminate depends on how the light is wired up. Can you clarify what cables you have at the light, and at each switch?

I haven't looked yet but I imagine it's the classic two wires between the switches & the third to the light & to the fusebox. It was wired up by an English DIYer (here in France) but that probably doesn't mean anything

 

[sparkyspike]

Have a look then and I'll show you how to wire it up. I still think you should get a 2-way (3 terminal) dimmer, but your plan of having a master switch and a dimmer can work, if that's what you want to do.

 

[sock99]

Have a look then and I'll show you how to wire it up. I still think you should get a 2-way (3 terminal) dimmer, but your plan of having a master switch and a dimmer can work, if that's what you want to do.

I'll have a look but I imagine it was done like this (don't know if french lighting standards are any different to English):

Untitled

• sock99
• 21 Jan 2009
• 2

 

[sparkyspike]

Ok, if that's how it's wired, then you can disconnect the wire in L2 of the switch and just use it as a normal switch. Then connect the COM of the dimmer to the corresponding wire at the other end. Then L1 of the dimmer goes to the light. Is your house wired in singles in conduit (gaine)? If so, and most French houses are, then your drawing is the most likely scenario. I can't remember whether Legrand use COM L1 & L2, or L1 L2 & L3 as its terminal markings, but you'll see what I mean.

 

[sparkyspike]

And in answer to your other question, it will be safe as long as you terminate the ends of the unused cable securely.

 

[sock99]

Is your house wired in singles in conduit .

Yes I think so. Is it important to put the dimmer on the wire that goes direct to the light (brown in the picture) or could it go in either place?

 

[sock99]

And in answer to your other question, it will be safe as long as you terminate the ends of the unused cable securely.

Sorry for the ignorant question but does "secure" mean more than just wrapping the end of the cable in insulating tape?

 

[ban-all-sheds]

I haven't looked yet but I imagine it's the classic two wires between the switches & the third to the light & to the fusebox.

The "classic" is actually 3 cores between the switches...

At least it is in England - I believe the "classic" way in France is latching relays and retractive switches.

It was wired up by an English DIYer (here in France) but that probably doesn't mean anything

It could mean a great deal that is not good - the French way of wiring houses, and the cables used, and the regulations, are quite different from ours in some very important ways.

Given how so many DIYers can't get it right over here I would be very wary of a French property worked on by one. Before you do any more work on it you should get it checked out by a French electrician in case your involvement in it ends up with you getting the blame for what the previous guy did.

It may all be perfectly OK, but you should not take it on trust.

 

[sparkyspike]

Yes I think so. Is it important to put the dimmer on the wire that goes direct to the light (brown in the picture) or could it go in either place?

No it can go in either place. I would terminate the cable using a terminal block or crimp and tape it up.

 

[ban-all-sheds]

I'll have a look but I imagine it was done like this

Why do you "imagine" it was?

Do you think it's a good idea to base your design work on imaginary scenarios?

(don't know if french lighting standards are any different to English):

They use different systems.

But if you don't know if, or how, they might be different you should learn about them before plunging in.

I would terminate the cable using a terminal block or crimp and tape it up.

I'm not saying that's not allowed, 'cos I have no idea, but do you know it definitely is allowed under French regulations?

 

[sock99]

Thanks for all the advice. I do of course understand it's all hypothetical at the moment & will not proceed till I'm 100% sure what the setup is.