Please help me wire my dimmer switch for my wall lights!

[novicesparky]

I have 4 wall lights and want to replace the switch with a dimmer.
In the box in the wall there are two thick grey cables each with a black, red and green wire - ok so far?
The black ones were taped up in a terminal block and there was one red wire in each end of the old switch.
The dimmer switch has 3 holes - the line with an arrow, L1 and L2.
I have tried just about every combination of wires to make these work and they don't - do I just keep the blacks in a block? if so how do I know which red goes into which other hole!!! Please help!

 

[johnny_t]

Assuming you haven't touched anything else, leave the blacks in their terminal block, one red in the line with the arrow, the other in L1.

Might be worth checking that the lihts you are trying to dim are dimmable. Energy-saving bulbs, for example, can't.

 

[novicesparky]

thanks - will try that but think that may have been one of the combinations I've already had a go at!! I don't get why the blacks don't go in anywhere - they do on the switch for the main ceiling lights!! Does it matter which red goes in which hole?

 

[johnny_t]

There are different ways of wiring switches. In the loop-in system, like for your ceiling lights, they use a piece of T&E to bring the live down from the ceiling rose above (usually on the red), and then the switched live goes back on the black when the light has been switched.

With your dimmer, both neutral and live are being fed to the switch. The neutral in is simply connected to the neutral out, and the live goes into the switch, and then switched live comes out, and then both of these (switched live and neutral) go directly to the lights.

If you skim through the for reference thread at the top of the electrics forum it explains in more detail.

 

[Belle427]

the blacks in the block maybe neutrals depending on who has wired it up,i have had switches where the terminals are arse backwards,try using L2 instead of L1 and the terminal with the arrow

 

[novicesparky]

have just rewired switch with blacks in terminal block and tried the two red wires in both holes but still no joy!!
Maybe I/ve buggered the switch by connecting the wrong way?? any other suggestions?

 

[Belle427]

any instructions with dimmer,they tell you the terminal configs

 

[johnny_t]

If one of your combinations involved both a live and a neutral inthe switch at the same time, you may have blown a fuse / tripped a breaker, though you would normally lose some other stuff as well.

 

[novicesparky]

I've just tried putting one of the reds in L2 but that hasn't worked either!!

If you can bear to reply again(!) please just talk to me in wire colours - I am a novice (and a girl!)

 

[novicesparky]

hi again - I don't think the fuse has tripped cos all the other downstairs lights come on when I put the fuse back!!!

 

[Belle427]

where on the switch are the terminals? are L1 and L2 on the bottom and the other on the top?

 

[novicesparky]

the instructions that came with the dimmer might well have been written in chinese!! they are very general and don't allow for two grey cables!!

 

[johnny_t]

To test if you have blown a fuse somewhere, turn off all your electrics at the main fuse box. Connect the two reds together, and the two blacks together (but not reds and blacks together). Turn back on at the fuse box and if your wall lights come on it sound like you have buggered the switch. If they don't, you have either blown a fuse or buggered something else, though to be honest I doubt you could bugger something else without blowing a fuse.

 

[novicesparky]

all 3 terminals on the dimmer are next to each other at the bottom of the little thing inside the switch

 

[Belle427]

your problem may be that the live feed needs to be in the arrow terminal and you have the 2 reds mixed up,it would have been in the common terminal of the old switch