Dimmer switch installation questions

[Yiannis]

Hi every one, I had a bedroom light switch replaced with a dimmer by a qualified electrician some months ago and want to get another in another room. Before tackling this myself I thought I’d look at the bedroom dimmer as a guide after reading up about dimmers online. Just two wires so looks simple. The one I have has been fitted into a 16mm backbox though manufacturers say min box is 25mm, should I add a 10mm spacer? What, if any difference will this make. When I use a voltage detector on the switch it detects voltage when switch is on, and off. Is this correct, it’s a push on/off dimmer. Any help appreciated by one confused amateur.

 

[telectrix]

you have a permanent live in C and switched live in L1. fit a spacer as this will help prevent the dimmer from overheating, apart from the fact that some dimmers will not physically fit in a 16mm box. wire up same as the existing switch. if the dimmer is metal faced, then you need to connect the cpc (earth) to the terminal on the faceplate instead of (or as well as) the back box. isolate the whole installation (main switch) before starting.

 

[Yiannis]

Thanks telectrix, not using metal faced dimmer and am ok about isolating. Do the permanent and switched lives mean the voltage detector always find voltage even when switch is off? Thanks again. Also thinking of using 25mm backbox when redecorating but spacer will be ok for now.

 

[Andy78]

I would use a 35mm box for any dimmer. Gives enough room for the dimmer module and ensures the wires are not crushed behind the module when the plate is fixed back.
Your use of a voltage detector (of unknown type) sounds a bit haphazard and worrying. If you don't know why it would be live with the switch off you would be better not taking risks and calling someone in to fit it for you.

 

[Yiannis]

Hi Andy78. I appreciate your concern but am quite happy to fit myself as I’ve fitted rocker switches quite safely before. A 35mm box would be ideal but I think a spacer will do as it meets manufacturers specs re space. Thanks for your help.

 

[Yiannis]

Thanks guys, new dimmer now in place and old dimmer has added spacer, all working fine.