2 lights into 1 dimmer

leeksie · 26 Jul 2007

I had two lights running to a double dimmer switch and I now want to run both to a single dimmer.
I would be grateful if someone could provide me with the correct wiring set-up.
Some details:
I have two (each black and red) cables running to the switch and the dimmer has three inputs (L1, L2 and ~).
I have tried all sorts of combinations and have managed to get one light working fine but the other seems to be either permanently on or permanently off.
Finally, when I try each cable/light on its own the first light works fine and the second light does not at all.
Any help gratefully received ...
Many thanks

electronicsuk · 26 Jul 2007

The wires should enter the box as two seperate pairs, each with one red and one black conductor. The two red cables should be the permament live supply from each fitting on the ceiling, and the black conductors the switched lives returning to the fittings.

As long as you are certain that both of the previous switches were protected by the same fuse/breaker in the consumer unit, try this:

- Take one red wire and connect into a single terminal (choc) block and push it safely to the back of the box, ensuring the cable will not get trapped by the mounting screws on the switch
- Connect ~ to the remaining red wire
- Connect both black wires to L1

If this doesn't work then some further testing with a meter may be required. Let us know how it goes.

EDIT: callEdsfirst makes a good point, one of those red wires might be a spare depending on how things were wired previously. Wire as suggested, but if you can't switch either light on then you will need to remove the red wire from the terminal block and connect to ~ on the switch, and vice versa with the remaining red wire.

CallEdsFirst · 26 Jul 2007

Whoa! You already "tried" multiple combinations!?!?!? Trial and Error is not a good way to stay alive with electricity! You need to find the two lives that were fed from the two dimmers and just combine them in the same terminal. Neutrals (if present) and Earths stay the same.

Im guessing you had one permanent live going into the common on the dimmers, probably jumpered to the common of the other one with a 2" bit of 1.5mm/1.0mm. That should now feed the common.....
DAMN YOU electronicsuk, just went to see what the OP had written and you have replied!

electronicsuk · 26 Jul 2007

CallEdsFirst said:
DAMN YOU electronicsuk, just went to see what the OP had written and you have replied!

Sorry

CallEdsFirst · 26 Jul 2007

If its two fittings in one room, isnt it likely that there will only be one permanent live? perhaps the first switched live will be the sleeved black from the same T+E and the second switched live will be a 6181Y 1.5 or a 6241Y 1.5?

electronicsuk · 26 Jul 2007

CallEdsFirst said:
If its two fittings in one room, isnt it likely that there will only be one permanent live? perhaps the first switched live will be the sleeved black from the same T+E and the second switched live will be a 6181Y 1.5 or a 6241Y 1.5?

Possible, but the OP states there are four wires, two red and two black. Either one of these is a spare and was never wired in the first place, or there are two permanant live feeds. Contrary to my original post, it actually seems more likely that one red wire is unused, but it isn't a good idea to assume so.

leeksie · 26 Jul 2007

Fantastic qick response - thanks!

Yes, the wires enter the box as two separate pairs (red & black each).

I am sure there is only one permanent live.

The original two switch set-up did have a 2" wire running between two terminals of the switch.

electronicsuk · 26 Jul 2007

leeksie said:
Fantastic qick response - thanks!

Yes, the wires enter the box as two separate pairs (red & black each).

I am sure there is only one permanent live.

The original two switch set-up did have a 2" wire running between two terminals of the switch.

I take it the other red wire (or at least one of the wires) was never connected? If so, put that one into a terminal block at the back of the box.

CallEdsFirst · 26 Jul 2007

Ahh fair enough

Contrary to my original post, it actually seems more likely that one red wire is unused, but it isn't a good idea to assume so

Nor is it good to repeatedly liven up the neutral/earth with random combinations! But im guessing with only four wires it has to be no more than 2 live and 2 switched lives with maybe one live redundant! Phew!

leeksie · 26 Jul 2007

Many thanks, chaps.

I will try the suggested set-up tonight and let you know how it goes (and I promise not to repeat my trial and error system!).

Cheers for now.

leeksie · 27 Jul 2007

No luck, I'm afraid.

Tried both reds in the ~ terminal.

The 'live' red made the first light come on but not the second.

The 'non-live' red made no lights come on.

I didn't try any other combinations

Any other ideas gratefully received.

Many thanks

securespark · 27 Jul 2007

Then the second light is goosed. Are you SURE it's working??

leeksie · 27 Jul 2007

Yes.

I've managed (through various combinations - see previous posts) to have the second light permanently on (with the light switch just controlling the first light only) and, even at one point, the lights alternately turning on and off with the switch (ie Light 1 on / Light 2 off - click switch - Light 1 off / Light 2 on!)

CallEdsFirst · 27 Jul 2007

By combination (no pun intended) of all of us, we have told you what "should" work, although one should never assume!

Might be worth getting someone in to test it now, bell out the cables and see what's what.

Nothing bad about trying and failing (assuming you are intact and breathing!) Admirable first attempt!

leeksie · 27 Jul 2007

Yep - I think you're right.

Many thanks to all for all your help.

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2 lights into 1 dimmer

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