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.