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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> installing dimmer switch https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1413127445 Message started by sami on Oct 12^th, 2014, 4:24pm

Title: installing dimmer switch
Post by sami on Oct 12^th, 2014, 4:24pm

I want to replace a broken two gang normal light switch with a two gang dimmer switch. When I took the broken switch off the wall it pretty much fell apart at the back (bits of plastic everywhere!). There are three live brown wires and three neutral wires, plus three earths connected to the back of the box. The three neutral wires are in a junction box but I can't tell where the live wires were connected as everything fell apart (there is a small connecting piece of live wire that must have gone somewhere??). The two gang dimmer switch has x 2 connection boxes, each with an L1 and L2 and what I assume is common (a wavy line). Can any help me with this wiring? I've wired up quite a few switches and lights in my time but I'm struggling with this one and can't find any on-line help thus far. Oh, and this is a brand new house. Thanks all

Title: Re: installing dimmer switch
Post by Lectrician on Oct 12^th, 2014, 7:09pm

You need to determine which of the Browns is a permanent live. This is best done with a meter. Once you know which the permanent live is, you connect this to an
L1, and bridge both L1's together. The two other Browns then go to the wavy line terminals (one to each). If the switch works with the left/right in the wrong place, swap the wavy lines around, or turn the whole switch upside down.

Working out which is permanent live is tricky without a meter.

You could connect two Browns together with a terminal block, leaving one live unconnected and isolated from everything (metal back box etc), standing clear, turning power on. If no lights come on, the UNconnected live is your permanent. If a light does come on, switch the power off, and choose another two Browns until you find a connected pair that do not cause a light to light. You then know the UNconnected core is your permanent live.

If you don't feel confident with doing this, dont! You are essentially turning the power on with live wires exposed, which is not te safest, especially with kids and others running around etc.