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I have bought a new ceiling light to replace an old-fashioned one.

I have 3 grey cables hanging from the ceiling: 3 red wires connected together and 3 green wires connected together and 3 black but only 2 are joined together the single black not marked with any insulation.

What I did at first is joined all the black together and connected them to the neutral of the ceiling light and the red to the live and the green to the earth but that caused the breaker to break.

I then rewired it without the single black wire and the light came on but it won't turn off by the light switch. The only way to turn it off is by the main breaker. I have replaced the light switch thinking it might have been faulty but that didn't solve the problem.

How should the light fixture be wired?

The single black wire should be connected with the L on the light fixture, and the 2 black are the neutral. What about the 3 red wires, where should they be connecting?

current wiring

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Old UK wiring

Old UK wiring was as shown below

enter image description here

A comes from the fuse-box/consumer-unit (possibly via other junction-boxes/roses for other ceiling lights). B goes to the next ceiling light. C goes to the light switch for this lamp.

However most electricians will not have cable type C with two red wires and will have used regular cable with a black and a red wire and will put red tape around the end of the black wire to indicate it is "switched live" and not neutral (as it's black colour would suggest).

From what I've read, sometimes they would connect C's black wire to position 3 (the other red live wires) and then C's red wire would be the switched-live return from the switch. Connecting the black to the reds would make it obvious to an electrician and that might be why no wire had red-tape on it's end.

Checking

If someone has removed the red tape, you can:

  • turn off the lighting circuit at the fuse-box/consumer-unit,
  • check there's no voltage present with a voltage tester (preferable non-contact type) and
  • separate all the wires,
  • use a continuity tester to see which red & black pair are connected/disconnected by the switch

enter image description here enter image description here
A typical Non-Contact Voltage detector (NCV) and a typical mains tester

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Finding which wires go to a switch using a multimeter (at least CatII 600V rated) on an isolated circuit (off at fusebox and tested for no 240V AC).

Your wiring (Guesswork)

Looking at your photo, I think the top of the screw-block connections from left to right are probably:

  • Live (3,4,5 in the diagram in this answer)
  • Earth (9)
  • Neutral (6,7)
  • Switched Live (2)

In which case your lamp should be connected at the bottom of the two right-most positions.

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  • hi thanks for ur help and its working now just swapped the red wires with the single black wire as that was the switch light as u guys have mentioned above.
    – hassan
    Sep 30, 2013 at 12:19
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This sounds like older UK wiring (or former colony) where red is typically hot and black is neutral. The sole black wire is probably a return switch leg, it should have been taped red, but this is often overlooked. This is why connecting all the black tripped the breaker. And connecting red and the black pair makes for an unswitched installation. The single black wire should be connected to the power side of the fixture and the two other blacks on the neutral side.

Mark the single black with tape so as not to confuse anyone in the future.

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  • hi you are right there its an old wiring. just to confirm this with you .... the single black wire should be connected to the L on the light fixture and the other 2 black wires to be connected on the N on the fixture what about the 3 red wires? should I leave them on their own? I have attached a photo of the current connection I hope this would make it clear.... many thanks for ur help
    – hassan
    Sep 30, 2013 at 8:21
  • I see you discovered leaving the reds on their own is the thing to do. I'm glad you got it working!
    – bcworkz
    Sep 30, 2013 at 17:02
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Your brown wire from the light (live) needs to be connected with the single black wire (switch live) that should solve it turning on and off

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You shouldn't have to touch the light switch at all. If you go to the first junction box, reveal all of the copper ends ensuring that they are not touching. carefully shut the breaker, and use a multimeter to find your "hot" lead. This hot lead should be connected to the white lead that leads to your light switch, and the black lead that is connected to your light switch is now your new "hot" lead. Reconnect that to the rest of your black leads and you will fix the problem. If you are having trouble finding which black and white wires go to your light switch, just turn your light switch to "on" and find out which two black and white wires have continuity (assuming you disconnected all wires)

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  • This is not a North American installation and there will be no white wires, so this advice could be correct but is wrong in context.
    – Sam_Butler
    Aug 20, 2020 at 8:54

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