Wiring a 2-gang, 1-way switch using a single 2-way cable

Discussion in 'General Electronics Chat' started by SharplyUnclear, Nov 1, 2014.

  1. SharplyUnclear

    Thread Starter New Member

    Nov 1, 2014
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    Hi there,
    I've got an old capacitive 2-gang touch switch which has failed, and I'm replacing with a standard switch. There isn't any labelling on the capacitive switch (i.e. no COM, L1, L2, etc.) to help with the new installation. The two switches each control half of a room's four lights, and it's a one-way setup. It should be straight forward to do, but it isn't...

    ...this is because the existing arrangement has a single, 2 way cable (i.e. four wires - red, yellow, blue, earth) coming in to connect the two gang switch to both of the lighting circuits (clearly something "clever" is being done inside a rose in the ceiling to branch things, but I don't have ready access to it to see what's going on).

    I can power two of the lights on one of the switches (using the red [on COM] and yellow [on L1] wires), but can't get the second circuit to function correctly. I've put the blue wire into L1 on the other gang and used a loop of wire to connect the two COMs, and I can read 240V current on my meter on the second circuit (reading taken from the light fitting). However, it won't actually power anything (I've taken a light fitting from the first circuit and re-installed on the second circuit to make sure that's not a factor).

    Does anyone have any suggestions on how the circuits might be wired, and what I should try to get the second circuit to light the fittings?
     
  2. #12

    Expert

    Nov 30, 2010
    16,278
    6,790
    Try telling what country you're in. Those colors are wrong for U.S.A.
    Somebody from the right country might know exactly what to do, if only we knew where you are.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    My guess from the terms, UK?
    Max.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    Is there any combo that powers the second circuit? How come you read 240v and nothing happens?, place a test lamp across the 240v reading and see if the lamp lights, it may be your meter is too high impedance to accurately read a load=sustainable voltage.
    Normally 3 conductors would all that would be needed?
    Max.
     
  5. SharplyUnclear

    Thread Starter New Member

    Nov 1, 2014
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  6. SharplyUnclear

    Thread Starter New Member

    Nov 1, 2014
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    I haven't found a combination that powers the second circuit. I've no idea why I read 240V but it won't power anything. I've wired a test lamp (actually I've tried two - a 240V regular bulb and a 12V LED with an integrated transformer) across the live and neutral where I took the 240V reading, and nothing happens (apart from an early "click" sound from the LED). I get a 240V reading when I connect across live and earth, and also between live and neutral. Neutral and earth give about 25v (impedance effect?).
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    But have you read the voltage when you place the lamp (load) across the 240v to see if it sustains?
    If not, it means there is some high impedance in the 240v circuit somewhere.
    Max.
     
  8. SharplyUnclear

    Thread Starter New Member

    Nov 1, 2014
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    0
    Thank you for your response: no, it falls off sharply.
    These lights (with the old capacitive switch in place) did become dimmer over the years, and I put it down to the switch itself. I wonder whether some of the wiring (perhaps at the junction box) has degraded over time?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    That indicates something else is going on there, it may be a case of tracing all the conductors out and see if there is anything else introduced somewhere, or a dodgy connection.
    Take care with 240v, it can bite badly!
    Max.
     
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