Help! Wiring a dimmer switch. What goes where???

[Kermit power]

Hi All,

I am trying to replace a busted dimmer switch, and having issues.

I took the old one off. I thought I'd carefully kept the wires in the right positions, but wiring in the new one isn't working.

There are 3 wires - grey, black and brown - and three terminals - L1, L2 and a weird, wavy X thing. I've now tried wiring all 6 possible permutations, and this either gives me a straight on/off switch with no dimming, dimming but the light permanently on, or just the light on with no dimming or ability to turn it off!

It may well be that the new dimmer switch is knackered, in which case I'll get it replaced, but I'd like to make 100% sure I've got it wired the right way first. Can anyone tell me which wire should go to which terminal?

I would look in another switch, but this is the only bit of two-way wiring with single switches in the entire house.

[homeimprovements]

surely if you have a 2 way lighting circuit you can look in the other switch to see what goes where

Assuming its been wired up correctly this is how we do it

black with brown sleeving should go to L2
brown to L1
and the grey with brown sleeving should go to the common

Hope this helps

[Kermit power]

homeimprovements said:

surely if you have a 2 way lighting circuit you can look in the other switch to see what goes where

Assuming its been wired up correctly this is how we do it

black with brown sleeving should go to L2
brown to L1
and the grey with brown sleeving should go to the common

Hope this helps

Doh! I didn't think about looking at the other end of this setup! I suppose I just assumed it would be different because it's not a dimmer switch.

Thanks.

[hairyben]

Whichever wire is used in com or x is the one you need to remember. L1/L2 can be switched over with no effect.

There are all different ratings for dimmers, failure in short time points to incorrect sizing. Just to make sure you replace it with the right item, whats the load (number of lamps, wattage) and type of lamp you're dimming?

[Kermit power]

hairyben said:

Whichever wire is used in com or x is the one you need to remember. L1/L2 can be switched over with no effect.

There are all different ratings for dimmers, failure in short time points to incorrect sizing. Just to make sure you replace it with the right item, whats the load (number of lamps, wattage) and type of lamp you're dimming?

The failed one was in for 5 years, and it's a physical failure (something inside has broken), so I'm not overly bothered by that.

I can't remember the exact ratings (I'm downstairs watching the rugby at the moment), but I'm replacing something like a 500w switch with a 400w one, and it's only running a single bulb, so I can't see that being a problem. I think it's just a switch supplied faulty.

[NiceCupOfTea]

It is an incandescant lamp isn't it? Not fluorescent/halogen?

[Kermit power]

NiceCupOfTea said:

It is an incandescant lamp isn't it? Not fluorescent/halogen?

Good old fashioned light bulb!

[NiceCupOfTea]

Does sound like the switch is knackered then!

[Kermit power]

NiceCupOfTea said:

Does sound like the switch is knackered then!

Looks like it! I definitely did have it wired up correctly the first time I tried it, so back to Homebase it is.

[hairyben]

sound okay on the loading.

Test it's not the dimmer by connecting COM to one of the strappers (L1 or L2) in a strip connector, make the other wire safe then re-energize the circuit. the switch on the other end should work the light.

[Kermit power]

I've just got home with a replacement, and wired it up as suggested above.

The replacement wasn't doing as expected either, so I've taken the front off the other switch to have a look how that one is wired, and it's different!

I'm assuming that the extra 2 wires in this one (blue and brown) are the feed from the mains, so I can ignore them? They're connected up to L1 and L2.

With regards to the other three, the brown goes to L1 as expected, but the other two have been transposed, with the black going to X and the grey to L2.

Would the swapped over black and grey fry the dimmer switch? I've now reversed them on the dimmer, so the same wires are connected at each end on all 3 terminals, and the replacement dimmer switch is again working as a simple switch with no dimming capability.

[Ganglandboss]

The brown and blue are the switch wires (the blue should be sleeved brown as it is now a phase conductor). The switches should be wired as per the above diagram. If you are still struggling, I strongly recommend you call an electrician.

[Kermit power]

Thanks for the diagram GB. That confirms that the numpty bloody electricians who rewired the house screwed up! They have definitely got the COM and L2 wires back to front.

This means I first fitted the dimmer switch linked up L1 -> L1, L2 -> COM, COM -> L2. Would that have fried the dimmer?

It is now correctly wired, but only working as a normal switch (ie, twisting the dimmer has no effect). Before I shell out for a third one, it would be nice to know if I need to find any other issues!