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I have recently had a conservatory built and want to wire an internal light fixture that has a live and neutral and Earth terminals.

I have removed my old security light and I am left with a cable existing of red, blue, Earth, and yellow with a red bit of tape on. My new light has a terminal for live, neutral, and Earth. So what do I do with the yellow cable. Can I just cap it off?

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    Your title and your question body don't agree very well, so it's hard to understand what you're asking. Please edit to clarify the situation. – isherwood Jan 14 '16 at 20:58
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    What colors are the wires in the cable with 3+earth wires? – longneck Jan 14 '16 at 21:10
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    Those aren't colors I would expect in electrical wiring (blue and yellow). That sounds like maybe you're using a wire meant for a thermostat or security data connections (not power!). Can you please include a pic or two? Is the light fixture for standard 120v power? – pbarranis Jan 15 '16 at 15:22
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    @pbarranis, the OP is most likely not in the US. Other parts of the world use different colors of wiring, and we get a lot of questions from non-US locations. – JPhi1618 Jan 15 '16 at 15:33
  • Thanks @JPhi1618. I mistakenly assumed non-US posts would go to a non-US site, like diy.stackexchange.co.uk or something. So "J Coe" - what country are you in? That may help us out a bit. – pbarranis Jan 15 '16 at 15:49
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Yes, just cap off the wires you do not need. Those are for future expansiom, you'll thank him later if you ever do something that needs it.

  • You may be right, but I think it's premature to give this advice without clarification. Blue & yellow wires? Security system? Too many weird things to me. Electricity is involved, so a little caution is wise I think. – pbarranis Jan 15 '16 at 15:33
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    @pbarranis, Check out this color chart for some colors used around the world. Blue and yellow is more common than white and black. The OP using the word "earth" is also a subtle indication that they are not in the US. – JPhi1618 Jan 15 '16 at 15:35
  • As per my answer the yellow wire may not be for future expansion. – AndyT Apr 26 '17 at 9:28
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Red, blue, yellow and earth are the old colours for "three core and earth cable" used for two-way lighting circuits in the UK. Any wire which could be live (depending on switch state) would have red tape on it to indicate this (other than the red wire, which is always used as one of the "could be live" wires).

The three-core-and-earth is normally used between the two light switches on a two-way circuit. It is not normally used between a switch and the light fitting.

I can think of two possibilities off the top of my head:

  1. The security light had both a switched live and a permanent live. So that when the switch is off the security light responds to movement (comes on for 30 seconds or so), and when the switch is on the light is permanently on. In this case the blue would be neutral, one of the red or yellow-with-red-tape would be permanent live and the other would be switched live. (NB There may be two switches in this setup. One "master switch" which turns on what I have referred to as permanent live, as well as supplying live to the other switch, which would control what I refer to as the switched live.)

  2. Whoever wired it up had run out of two-core-and-earth but had some three-core-and-earth lying around, and used that. In that case one of the wires would probably be unconnected at both ends.

A key question here is: What were the wires connected to before you took the old security light off? But I guess it's a bit late for that now.

A practical thing you could do is to connect all the wires separately into connector blocks. Then turn the power back on, try flicking the switches, and use a voltage tester to check which wires might become live. This would be able to detect situation 1 above. It wouldn't confirm situation 2, though it could confirm that it's a possibility.


(All this is clearly too late 15 months after you asked, but this might help someone in future with a similar situation)

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