Light switch in loft seems wrong?

Discussion in 'General Electronics Chat' started by turnbui, Feb 4, 2009.

  1. turnbui

    Thread Starter New Member

    Feb 4, 2009
    The light switch in my loft has 2 2 core wires going to it. The red wire of each go to each side of the switch. The 2 black wires are twisted together at the point where the insulation has been removed. These are not attached to any part of the switch. Has someone used one of the red wires as a black one. I can't find where these wires come from.
    Thanks for any help.
  2. leftyretro

    Active Member

    Nov 25, 2008
    The switch is opening or closing the circuit and will work as found. One of the cables is coming from a voltage source and the other cable is going to the load, perhaps a light in the loft? If you are not experianced with home wiring you should probably not attempt to rewire without proper instruction.

    The fact that the color red is used tends to mean someone used a non standard home AC cable, as at least here in the US, the standard colors are black and white and if a 3 wire cable, a green wire used for a safety ground.

  3. thingmaker3

    Retired Moderator

    May 16, 2005
    In a correctly wired North American residence using type "NM" cable, the neutral wires (white) would be connected together in a listed wire-nut. The hot (black) in from the breaker would be on one side of the switch and a switched hot (black) would go to the lumnaire from the other side of the switch. The ground wire (bare or green) would connect to the switch ground, the box ground, and the luminaire ground.

    There a some permitted variations on the above, ie running the white wire unbroken, using a "Wago" instead of a wire-nut, using "MC" cable or using wire in conduit, etc.

    There are, of course, many ways to wire something unsafely and still have it work. If in doubt, hire a licensed electrician.
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    Is this what you mean?

    black1-----------------xxxjoinxxxx-------------black2 (this is the neutral)

    Red1.......................\vdots switch ......Red2 this is the switched live supply

    Black1 & Red1 come from the supply.

    Black2 & Red2 go to the fitting

    You will have to decide which is which. If you have a meter or tester, the red which is live whichever way the switch is set, is the supply.

    This is an old, but legitimate wiring arrangement.
  5. turnbui

    Thread Starter New Member

    Feb 4, 2009
    Studiot you have it. Thanks.
    Thanks to everyone else.
    Here in the U.K. we used to have 3 core cable
    black - neutral, red - live and green - earth.

    We changed a number of years ago to
    blue - neutral, brown - live and green/yellow - earth.

    I want to use the loft as a study and want to put in an extension with 3 plug sockets on it. Should I just connect itn to the 2 red wires on the zwitch or go to the light it operates and connect to it's red and black wires?
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    No you will have to run new cable, in the new colours.

    The old red/black will not have enough current rating to supply sockets.
    Further there is no earth which is now required for all circuits.

    Either get a competent electrician to fit the points or run a standard extension cable from downstairs.

    see post #45 of this thread