Wiring up a two-gang, two-way, dimmer switch - help!

crookesm · 30 Aug 2004

I am attempting to replace an existing two-gang two-way rocker switch with a new two-gang two-way dimmer switch. Thinking I new it all I removed the existing switch before making note of the existing connections.

Surprise, surprise - I can't get the new switch to work! javascript:emoticon('

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The wires coming out of the wall are as follows:

2 red (only one of them tests live)
2 black
2 sleeved green

The existing switch has a piece of red wire connecting both COMs on the switch together (I know this because this is the one piece of existing wiring I didn't remove). I'm guessing therefore that the live red wire went into one of the COMs.

However, that leaves four other connections - 2 L1s and 2 L2s and five available wires (I'm guessing the only candidates are the 1 remaining red and 2 blacks though). I cannot even begin to guess how these fit together.

Any help or pointers in the right direction would be most appreciated.

Thanks...

Lectrician · 30 Aug 2004

If it deffinantly fed 2 sets of lights, then i would think your best bet would be to try the below.

Put both reds into the coms, with the link also, and then one black to each L1.

Check it works, if any lights remain on constantly, then the 'dead' red needs to be put in one of the L1's.

You should use some red sleeve on the blacks.

Hope that helps

crookesm · 30 Aug 2004

Genius - thanks very much - it works.

There is one more piece to the puzzle though - what do I do with the two earth cables (I assuming they're earth as they are both sleeved green)? Should I just tie them together and connect them to the metal box?

Also. I have an earth cable coming out of the metal faceplate on the switch. Should this also be connected to the metal box?

Lectrician · 30 Aug 2004

yup, connected all earths to the backbox.

crookesm · 30 Aug 2004

Everything seemed to be working correctly

- however

...

There are two dimmer switches on the plate - the left one controls the downstairs hall light (this one works fine).

The right one controls the two upstairs hall lights (you can turn them on and off from this switch). However, once the upstairs lights are on - the upstairs lightswitch cannot turn them off. However, if the upstairs lights are off (they were turned off by the downstairs dimmer) - the upstairs lightswitch can turn them on and off OK.

A description of my wiring is as follows (hope it makes sense - I couldn't figure out how to attach an image):

Left dimmer: red wire (live) into COM; black wire into L2; red wire from COM to dimmer 2 COM

Right dimmer: red wire (doesn't test live) into COM; black wire into L2; red wire into COM from dimmer 1 COM.

Could it be that I should move the black wire on the right switch to L1? I'd appreciate any insight you have - I'm a bit loathe to experiment here!

Lectrician · 30 Aug 2004

OK, differnt wiring coming up.....

The red that meters live to COM, and the link to the other COM.

The black from the same cable as the LIVE to an L1 on one switch for hall.

The red and black in the other cable, RED to L1 and BLACK to L2 on the other switch (or visa versa).

Didnt realise it was 2 way, this will sort you, sounds like it is wired in the old school way. Where you from?? Every house near me is wired the way yours appears to be

Lectrician · 30 Aug 2004

Left dimmer is hall.

Earths omitted, but connect as before.

crookesm · 31 Aug 2004

Thanks - I'll try this out tonight and let you know...

I live in Doncaster by the way.

Lectrician · 31 Aug 2004

Nowhere near me! Hope that setup works for ya.

crookesm · 1 Sep 2004

It works! Thanks for that - I would never have figured this out on my own!

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Wiring up a two-gang, two-way, dimmer switch - help!

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