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Help. Changing 25+ year old light switch.

Discussion in 'Electrics UK' started by Jacob Lang, 4 May 2020.

  1. Jacob Lang

    Jacob Lang

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    Hi everyone, I’ve been decorating and wanted to switch out a light switch from an old plastic standard one to a metal dimmable one.

    however not sure which wires to connect. Any help/advice much appreciated, thanks.
     

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  3. winston1

    winston1

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    You can’t use a metal switch as there is no earth wire there.
     
  4. sparkwright

    sparkwright

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    Does the switch come with some wiring instructions?

    You need to confirm if there is an earth available at the switch. It appears to be wired in metal conduit, so hopefully an earth can be achieved from the earth terminal in the back box.

    The two joined red wires together in L2.

    The single red wire in com.

    Then you need some green and yellow wire from earth terminal in the box to the earth terminal on the new switch.

    You may struggle getting the two reds together into the L1 terminal, in which case you may need to put them in a connector block, with a single piece of short wire to the L1 terminal.
     
    Last edited: 4 May 2020
  5. terryplumb

    terryplumb

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    The metal conduit MAY be providing the earthing. You would need to do some testing to establish if it is.
    Or just fit a dimmer with a plastic face plate that doesn't require an earth.
     
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  6. sparkwright

    sparkwright

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    You are wrong, it is likely an earth is available there.
     
  7. winston1

    winston1

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    Why?
     
  8. sparkwright

    sparkwright

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    Because it is wired in metal round conduit, and if it tests out ok, an earth can be obtained from the earth terminal on the back box.
     
  9. Jacob Lang

    Jacob Lang

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    Yes mate, these are the instructions I got, didn’t get any additional wires or anything like that.
     

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  11. sparkwright

    sparkwright

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    Ok, in that case:-
    The two reds to L2.
    The single red to com (the one with the sqigglely arrow symbol).

    L1 is left empty.

    And an earth wire from back box to earth terminal on the metal switch plate.
     
    Last edited: 4 May 2020
  12. sparkwright

    sparkwright

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    But before you start, best to confirm there is an earth available. Have you a multimeter?
     
  13. Jacob Lang

    Jacob Lang

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    Okay thanks mate, so I can just buy a wire and connect the two points. I think I do have a multimeter one that I used to check the battery on my motorbike. I’m assuming that’s ok to use, if so which combination of wires should I try?
     
  14. Jacob Lang

    Jacob Lang

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  15. sparkwright

    sparkwright

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    To give you a rough idea if the metal switch box is earthed, turn all power completely off.

    On the continuity or ohms setting of the meter, put one lead on the metal back box, put the other lead on the faceplate screw of a nearby 13amp socket (don't undo the socket).

    If you have continuity, ie the numbers move about, you should have an earth there. You may need a long lead to do this.

    This is by no means a proper earth test, guidance only at this stage.
     
  16. sparkwright

    sparkwright

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    That arrow symbol with the yellow border just before 6 o'clock will do for a quick continuity test, it should beep when the two leads are touched together.
     
  17. Jacob Lang

    Jacob Lang

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    Huge help, thanks a bunch for your time and advice, hopefully can get this sorted now.
    Thank you to all who comments also.
     
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