12v at light switch

Discussion in 'Electrics UK' started by Ohmslaw, 9 Apr 2019.

  1. Ohmslaw

    Ohmslaw

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    Just wondering why there would be 12v showing on my meter when I put my tester across my cables at the light switch?

    The room only has 1 light switch, but wired as a 2 way with both L1 and L2 being used. I've disconnected everything, and between L1 and L2 I get 12v, between common and L2 I get 240v, and common and L1 I get 12v.

    This indicates to me L2 is actually common, but just wondering why the hell there is a cable in L1, and why the 12v?
     
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  3. winston1

    winston1

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    Electromagnetic induction and a high impedance meter.
     
  4. EFLImpudence

    EFLImpudence

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    Common does not mean live. It is the switch terminal which connects alternately with L1 and L2 when the switch is operated.

    In your method of two way switcing, it is not the Common which is the supply Live.

    upload_2019-4-9_19-48-14.png


    In another method it is.

    upload_2019-4-9_19-51-2.png
     
  5. Ohmslaw

    Ohmslaw

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    Cheers for info. I know about electromagnet induction, but cant remember it showing 12v before (been a while)

    Just puzzled me as I only have the 1 light switch but this 1 switch is wired as it being 2 way. My only other thought is they have just just put the neutral into L1 rather than a connector, and switch wire into Common.

    Could prove this by going to light or board, but was lazy and wanted to see if there was an easy explanation before I went and did it!
     
  6. Taylortwocities

    Taylortwocities

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    There is no neutral connected at the switch.
    Look at the schematics. Can you spot where the neutral is connected?
     
  7. Ohmslaw

    Ohmslaw

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    I know theres not meant to be a neutral, but cant think why else there another core there.
     
  8. Taylortwocities

    Taylortwocities

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    There may be a hidden/blanked off switch somewhere. I’ve seen several examples of this where rooms have been altered over the years.
    Can’t say for sure without being there with a test meter.
     
  9. aptsys

    aptsys

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    Unlikely to be induction - the mutual inductance between those cables and another carrying enough current to induce a voltage into it to measure with a DMM is not hugely realistic. Much more likely to be capacitive coupling.
     
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  11. Ohmslaw

    Ohmslaw

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    Is this normal at a light switch?
     
  12. Ohmslaw

    Ohmslaw

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    Actually opened up a switch in a different room, and the same wiring and the same voltages is there - even though it's still just 1 light switch in the room
     
  13. Ohmslaw

    Ohmslaw

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    This is the wiring (wires closest). This one is a 3 gang
     

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  14. Ohmslaw

    Ohmslaw

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    So in this case, when light is on, Common and L1 I get 12v. C and L2 I get just continuity, and L1 and L2 12v.

    When light is off, C and L1 I get continuity. C and L2 i get 240v, and L1 and L2 I get 240v
     
  15. Taylortwocities

    Taylortwocities

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    When testing voltages like that, you should be testing between EARTH (or neutral) and the various cables.
    There’s no knowing what you’ll find in other cases.
    For instance. If you test between one of the L terminals and the COM, you may be measuring from a live conductor, to the switched live, through the lamp and on to neutral.
    Look at the diagrams and try and understand what you are prodding.
     
  16. Ohmslaw

    Ohmslaw

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    Cheers for help, appreciated
     
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