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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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A diagram would be helpful, as your explanation is very difficult to understand –  BlueRaja - Danny Pflughoeft Sep 29 '13 at 18:53
    
Possible duplicate: diy.stackexchange.com/a/31318/2196 –  BMitch Sep 30 '13 at 12:40

2 Answers 2

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

enter image description here
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 '13 at 12:19

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 '13 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 '13 at 17:02

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