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I went to replace the light fitting in our kitchen (UK). After taking the fitting off, it looks like two negative wires are going into the fitting (three wires from the ceiling, two joined, two into the fitting). The three positive wires are joined but not connected to the fitting and ground is connected. The light still works.

Positive and negative terminals also aren't marked on the fitting.

Does anyone have any idea what's going on here?

Images of wiring: https://drive.google.com/file/d/1qBNcsY2wrFdG-2atoGVej6nGlbbTNM66/view?usp=drive_link, https://drive.google.com/file/d/1cgiL0as3Iyh_PEFJX7hpzrshDdOT4JFP/view?usp=drive_link, https://drive.google.com/file/d/13N9sL8Hg8CzHpUnQr-DFopfdvsC5Kwze/view?usp=drive_link, https://drive.google.com/file/d/1y85KfQDjWqEqM8MKAKwKCCNbe8eOv9t2/view?usp=drive_link

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  • Probably a switch loop. One of the live wires goes to a switch, and the power comes back on the single black. Do not know your local electric code, so cannot tell if it was done to code.
    – crip659
    Commented Jul 24 at 10:46
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    The odds that your ceiling light is positive ground Direct Current are very, very small. Normal power delivery worldwide is Alternating Current, in the UK 230-240VAC Live, Neutral, and Earth with the possibility of some higher voltages if being served more than one phase of power. So there aren't positive or negative termnals at all. Please engage in some self-education about what you are fooling with before you get hurt.
    – Ecnerwal
    Commented Jul 24 at 10:57
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    @Ecnerwal's right, and you've probably got old colour wiring with red and black that look like positive and negative. Black is normally neutral but can be switched live. It often wasn't labelled or sleevedin old installations. somewhere tucked away there should be a join in red (live) wires, one of which will be paired with one of your black wires. In new installations, brown replaces red and blue replaces black, and marking switched live is more common
    – Chris H
    Commented Jul 24 at 11:45
  • Now the pictures have loaded my previous comment is demonstrated apart from 'tucked away' and an answer is possible
    – Chris H
    Commented Jul 24 at 11:46

1 Answer 1

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As I said in the comments, following on from Ecnerwal's point, you have old mains wiring colours (which is fine) and the switched live isn't sleeved to make it clear. Here's one of your photos marked up.

wiring, labelled Note the 3 red live wires. Two of those go to the previous and next lights in the circuit, the third goes to the switch.

The single black wire connecting to a white wire in the lamp is the return from the switch, live when the switch is on.

The 2 black wires are neutral. They also connect to a white wire in the lamp (which doesn't care which way round live and neutral are, because that's how AC works).

The green mated to green/yellow is earth.

So your new fitting needs to connect to:

  • Earth (unless it lacks an earth terminal, which is possible if it's all plastic or "double insulated" (an old term but clearer than the new "class 2") - green
  • Neutral - double black
  • Live - single black (NB if it has a built in switch you may want to do things differently.

Turn off the breaker serving this circuit (which may mean all your lights and may include smoke/burglar alarms) before starting work and check you really have no power here.

Background for international readers: UK main wiring uses red or brown (depending on the age of the installation) for 230V "live" (we don't call it "hot"), black or blue for neutral, and bare copper sleeved with green or green/yellow for protective earth. Earth wires have been required for a very long time, and the vast majority of domestic wiring is "twin and earth" PVC sleeved 3-core cable as shown here. Single phase is the norm in homes, and always single leg, not 120-0-120.

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  • Thanks for the detailed answer. When you say "doesn't care which way around, because that's how AC works", does that mean I could have connected either black wire to either terminal in the new fitting? Also, please could you explain how you knew the single wire was coming from the switch just for my understanding? Thanks
    – James Johnson
    Commented Jul 24 at 14:20
  • @JamesJohnson yes, either black wire to either of the (non green/yellow, not marked ⏚, PE or E) terminals in the new fitting. The new fitting may mark L and N. It still doesn't matter which way round for it to work properly, but running the single black to L and the double to N is tidier and less likely to confuse future you.
    – Chris H
    Commented Jul 24 at 14:37
  • As for the switch wiring, I knew before looking at the pictures (patchy WiFi here), because this setup is very common. The lighting wires run in the ceiling to the fitting, with another run from the fitting to the switch and back. The permanent live in that uses the standard live colour, red, and the switched live uses the other core, black. Then that's also the only use for a wire that connects only to the light fitting. The bare wire is always earth and needs to be connected at both ends in case the switch is metal or in a metal box. Even if it's currently all plastic, that may change.
    – Chris H
    Commented Jul 24 at 14:42

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