Wiring of 1-way 2-gang dimmer - please help

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19 Oct 2011
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Aberdeenshire
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Hi

I have recently replaced an old plastic 1-way 2-gang rocker light switch with a 'Crabtree Platinum range' 1-way 2-gang dimmer (250W rating). One switch controls a single 40W GLS lamp in the wardrobe, the other controls 6 GU10 35W downlighters in the bedroom.

I have wired the dimmer exactly the same as the original switch (even taking the precaution of taking a few photos on my phone in case they got mixed up), but when I power up the circuit....

- the single GLS lamp comes on and dims correctly but the switch controlling the downlighters will ONLY come on & operate if the other (GLS) dimmer is also on. I initially thought the load might be the problem (6x35W plus 40W = 250W) but took 4 of the 6 halogens out making the load 110W and the problem is still there)

There are a total of 4 cables coming out of the wall - I believe one is for the GLS lamp only and the other 3 for the downlighters, so there are lots of wires! All neutrals are joined in a terminal block, as are all the earths (except the one to the backbox/faceplate), so presumably only the reds (and one brown) need to be connected.

The original switch:
Left side (looking @ back of switch): Downlighters - brown to L2, red to Common (both with bit of blue tape to identify)
Right side (GLS) - red to L2, red to Common
Plus red wire crossing from Common left to common right

The dimmer:
Left side (looking @ back of switch): Downlighters - brown to L2, red to Common (both with bit of blue tape to identify)
Right side (GLS) - red to L2, red to Common
Plus red wire crossing from Common left to common right

If anyone can be of any help, I'd greatly appreciate it .... I've read lots of previous posts on dimmer wiring (my, aren't they a common source of questions!) but still can't work it out.

Thanks :D
 
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You need to check that you have put the permanent live in the common.
Rather than L2. you need a voltage indicator.
Sounds like you have got them mixed up.
 
I know what you've done.

See the diagonal line moulded across the back of the original switch?

That shows the allocation of the terminals to the switch gangs.

See this: //www.diynot.com/wiki/electrics:twogang

You assumed that the conductors across the top went into one of the dimmer modules COM to COM,L2 to L2 etc, and the ones across the bottom into the other dimmer module, whereas what you should have done was to take L2 from the top and COM from the bottom into one dimmer, and COM from the top and L2 from the bottom into the other dimmer.

Swap the L2s over.
 
Thanks for your replies guys.

BanAllSheds - I tried that but now the other side of the dimmer controls both sets of lights (i.e. exactly the same as before just swapping left for right). Looking back at my pictures, I definitely connected the wires as per the original rocker switch - I put the blue tape on at the time to identify them before I took the rocker off). Obviously I'm still missing something - any ideas as to what else I can try?

Thanks again
 
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