Wiring 3 gang switch - light is always on or always off

Postby sarahaddyman » Wed Feb 18, 2009 4:39 pm

I have a three gang switch in my hall way. The switches are for the landing light, the hall light and the porch light. The landing light and hall light both work, but the porch light doesn't.

I turned of the electricity and opened the cover of the porch light, assuming the bulb had gone - to find the light wasn't wired up. (It's never worked in the time I've lived here.)

There are two red (live) wires, which are connected together. There are two black (neutral) wires which are separate. There is no earth wire, so I have replaced the light with a new one from B&Q that does not require an earth, just to be on the safe side.

If I separate the red wires, the landing light and hall light don't work. If I connect the black wires, the trip switch goes as soon as I put the electricity back on. So I know the two red need to stay connected and the two black ones need to stay separate.

If I wire the light up to both red wires in the live connection and one black wire in the neutral connection either the light doesn't work at all or it is permanently one, no matter what position the light switch is in.


If it does, will buying a new three gang switch (for the instruction leaflet that comes with it!) to rewire it solve my problem? Or is it a more serious problem that requires an electrician?

(I've rewired a new security light and changed standard two gang switches for dimmer switches, so I'm competent with the basics.)
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Simply Build It

Postby TheDoctor4 » Wed Feb 18, 2009 5:43 pm


Have you had a look at the DIY Projects area at all: http://www.diydoctor.org.uk/projects.htm There are numerous projects related to electics that may be able to help you.

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Postby jtc » Wed Feb 18, 2009 7:02 pm

sounds like the switch wire is missing, any chance of you posting a picture of the wires in the switch and wires at the light, or find a friendly leccie with a tester it shouldn't take long to trace it
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Postby kbrownie » Wed Feb 18, 2009 8:41 pm

Quote "There are two red (live) wires, which are connected together. There are two black (neutral) wires which are separate"
Just to be sure are these wires at the light fitting in the porch and the three gang is only wired up to to two other fitting so there is a spare switch on this gang?
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Postby singer » Thu Feb 19, 2009 12:22 pm

You'll probably find the one black wire at the porch light is a neutral and the other black wire is a switched live which should have red or brown sleeving or tape on it to indicate it is a live and not a neutral.

Connect your light fitting to these 2 cables and make sure the 2 reds are connected together and insulated.
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Postby sarahaddyman » Thu Feb 19, 2009 5:24 pm

Thanks for your responses, but I've managed to get the answer from electrician4u.net - I've posted it below in case anyone uses this thread to answer the same question.

The two red are like you say are live they will be looping
in and out and no connection to the light is required.

The two blacks are not both neutral. One is a switch live and one is the neutral - that's why they are separate. One of them should have been marked red with tape or sleeving.

If you connect the fitting to the two blacks it should work ok but the polarity of the wires should be identified and marked. The one which set the light as always on is the live wire, the one which set the light as always off is the neutral.

I've followed these instructions and my light now works. :D
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Postby singer » Thu Feb 19, 2009 5:52 pm

As I suspected.

Well done.

Problem solved
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