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Trying to install a double dimmer switch on weird wiring, please help

Discussion in 'Electrics UK' started by JosieJo11, 13 Apr 2021.

  1. JosieJo11

    JosieJo11

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    Hi, I'm trying to replace a double switch with a double dimmer. They are both one way so should be simple but when I opened the old switch the wiring doesn't look like anything I've seen or can find on Google.
    Three red wires wired in to the top L1, L2 and com and three black wires wired into the bottom L1, L2 and com.
    So, I did the obvious and labelled each wire and then transferred the wires to what I thought was the same on the dimmer but neither dimmer is working. Can anyone please advise on what this wiring layout is? Please help! Jo 20210413_143638.jpg 20210413_143638.jpg 20210413_143226.jpg 20210413_143201.jpg
     
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  3. JohnD

    JohnD

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    No they aren't.

    Two-way switches have three terminals each, arranged in a triangle, with one at the top (or bottom) and two at the bottom (or top)

    Your switches are two-way.

    In yours, the one marked "com" is the tip of the triangle, and the L1 and L2 are the two on the base of the triangle. You will notice that one triangle is point-up and the other is point-down.

    You must keep the three wires from the left-hand switch, and the three wires from the right-hand switch, apart, and not mix them up.

    Put the wires back into your old switches. Do they work? If they immediately blow the fuse/trip the breaker, you have made a mistake. If both switches work perfectly in all combinations of switch, mark the wires again, and reconnect three at a time into three terminals of the new, 2-way switches that you will need to buy.
     
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  4. JosieJo11

    JosieJo11

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    Thanks for responding so quickly John. I hope your reply will help me fix things tomorrow. When I said they were one way I just meant that there aren't any other switches controlling the lights, just this double switch. The left for the kitchen light and the right for the dining area light. Sorry if I used the wrong terminology :)
     
  5. JohnD

    JohnD

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    I bet there are, but they might have been hidden behind furniture, inside cupboards, or perhaps wallpapered over by a previous occupant. That type of switch is only used when there is another one, somewhere.

    One-way switches only have two terminals, and two wires, but you have three wires, which can only work with 2-way switches.
     
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  6. JosieJo11

    JosieJo11

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    Oh, that's confusing. The other switch must have been removed and plastered over - there is swirly artex on the walls:-\
    So does that mean I can't put a double dimmer switch there instead? Sorry to ask so many questions.
    I will have a go at putting the old switch back on tomorrow as you suggest to see if I miss labelled the wires but I really would like to put dimmers in. At the very least I have to get rid of the ghastly brass switch plate! I've put up with it for 5 years and I've had enough! It has to go :D
     
  7. JosieJo11

    JosieJo11

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    Sorry, meant to say thank you so much for your time!
     
  8. JohnD

    JohnD

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    I can't see anything to stop you putting a 2-way double dimmer in. Just assume that the other switch is hidden, somewhere, and will not be operated. It might turn up one day. Probably next to where a doorway used to be.

    Dimmers need to be matched to the type of bulb you will be using. Probably Dimmable LED lamps, these days. They may have a minimum and a maximum power rating on the dimmer.

    Old dimmers as used in incandescent lamps will not work, and most LEDs are not dimmable.
     
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  9. 333rocky333

    333rocky333

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    You can still have your dimmers, just because there wired as 2 way it dont matter
    Whether the other switches are still there or now gone, as long as that old switch worked ok then the 2 new dimmers should work fine providing the bulbs or whatever you are dimming are suitable to be dimmed,
    Tomorrow post a pic of the back of the dimmer, you will also need some earth wire to strap from the box to the dimmer if its metal
     
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  11. winston1

    winston1

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    Rather concerned that your old switch appears to be metal with no earth connected to it. If your new dimmer is metal connect the earth. If you give up and reconnect your old switch connect the earth as well.
     
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  12. securespark

    securespark

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    There are signs of a CPC in the back box.
     
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  13. JohnW2

    JohnW2

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    There are. I suppose it may have pulled out of the terminal on the faceplate when it was pulled forward.

    JosieJo: Where does that wire with the green and yellow insulation in the back box go to? Does it perhaps have a 'loose end' (i.e. doesn't go anywhere)?

    Kind Regards, John
     
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  14. SUNRAY

    SUNRAY

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    just hiding upload_2021-4-14_10-15-2.png
    First, well done for labling the black wires and the photos. The info JohnD has given is correct, there will be another switch position somewhere but it's also possible a wall has been removed at some stage and the wiring moved into a junction box above the ceiling or something similar.
     
  15. JohnW2

    JohnW2

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    Are you saying that you think (and/or 'are confident that') the G/Y is connected to that terminal?

    Kind Regards, John
     
  16. SUNRAY

    SUNRAY

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    MMm now I've tried to zoom in:
    upload_2021-4-14_13-46-59.png there are a couple of bright spots above orange which I too to be the copper and above the yellow lines which I took to be the sleeve, not so sure.
     
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  17. JohnW2

    JohnW2

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    Quite. As I implied, I'm 'not so sure', either, which is why I asked the OP 'where it went'!

    Kind Regards, John
     
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