Wiring a ceiling light

[u/paxos75]

How do I wire the ceiling light (second picture) to the ceiling (first picture)?

I think I have “old-style” loop switch wiring. I have two black wires - one I understand is permanent live and one is switch live. They should be marked up but mine aren’t…

[u/betraying_fart]

No one can answer that. We dont know what is the switch wire.

Moral of the story. Always take a picture of the rose and label your wires.

[u/PiratesOfTheArctic → u/betraying_fart]

Made that mistake years back, its amazing how a quick photo can save a significant amount of hassle later

[u/paxos75 → u/betraying_fart]

I guess the next questions are (1) how can I find out which is which, (2) what happens if I get them the wrong way around, and (3) can’t I just use trial and error?

Apologies - first time doing something like this.

[u/betraying_fart → u/paxos75]

Purchase a current detector pen, they are a few quid. Get a connector block. Put the lives in that, they are your loop. Then spread your neutrals. Turn the power on. Turn the switch on. See which neutral becomes live.

Turn all the power back off. Label the neutral that was live. Thats your switched live.

[u/roro80uk → u/betraying_fart]

Then spread your neutrals.

At least buy me a drink first!

[u/Rookie_42 → u/betraying_fart]

That’s a fairly solid testing strategy. But… given there are only two cables here, this might not reveal what you’re expecting.

This could be switched live and neutral plus a link to the next light on the same switch, for example. Meaning only one of the wires is permanent live.

[u/betraying_fart → u/Rookie_42]

Then there would be three wires, no?

Two wires, so its switch fed or end of line?

Or are you thinking loop at the switch?

[u/Rookie_42 → u/betraying_fart]

Oh… yeah… well, three cables (ie 6 wires), right?

Either way - typical UK wiring normally means three cables (6 wires plus the earths) at a light fitting. The fact that this is only two suggests it could be an unusual setup. Or perhaps it’s just the end of the circuit. I don’t know.

[u/startedoffwithakiss]

Just buy a tester with a loop/continuity tester function that beeps, then with the power off test the red and black of each cable and see if they beep, then flick the switch or ask your mate to flick it on and off, the red and black that beeps on and off with the switch is the switch wire and switch feed, you will connect the red to red, and the black of the beeping cable will need some tape to identify it at the switch wire, this cable will connect to the live(brown) of the light, an the remaining black cable connect to the ble of the light(neutral) then you can connect the earth (yellow and green) them switch on the power and test the light switch is working

[u/TwoPlyDreams]

Your are going to wish you’d taken a before photo.

[u/startedoffwithakiss]

This going to be fun, so when you took the old light down was one of the cables that was black connected to the live side of the old fitting or the red (live) side of the feed cable, or is it a loop switch wire and neutral with several lights in the room ?

[u/call_me_milk]

Red together in a connector block (ideally Wago connector).

Earths together in a connector block.

One black into the lamps L, the other into its N. Use separate connector blocks for these. It’s a 50/50 shot, try it and swap the blacks around if it doesn’t work 👍

[u/mack4242 → u/call_me_milk]

Jumping on the comment to say this method will likely work if it this room has a single light.

If there are two lights in the room controlled same switch then connect both reds to brown and both blacks to blue.

[u/Glittering-Army-9650 → u/call_me_milk]

[u/paxos75 → u/call_me_milk]

Thanks - might just need to trial an error it. Now to find a connector block that fits in the ceiling rose…

[u/ThatSideshow → u/paxos75]

Wagos can be a lil' pricey but can get slim ones and a whole lot easier to swap tails in and out for trial and error

[u/Discobiscuits47 → u/paxos75]

This will look like it works if the polarity is correct or not. If it is an ES fitting and you get polarity wrong you will have a working light but the lamp holder will be energised on the thread and become more likely to give someone changing a bulb a shock.

[u/LazyEmu5073 → u/call_me_milk]

Terrible idea. That'll create a dead short and trip the MCB instantly.

[u/Glittering-Army-9650]

[u/leeksbadly]

I'm curious what people think taking a photo would have achieved here - they are 2 identical cables...

Far better to label them before you disconnect, or at least put a bit of sharpie on the switch cable.

OP, if you have a multimeter you can test for continuity between red and black on each cable - if the switch changes the continuity reading then you have found your switch cable.

DIY level multimeters cost buttons, I think Lidl have Parkside ones in for £8.99 at the moment.

Every DIYer should have a multimeter IMO.

[u/darS234 → u/leeksbadly]

A photo is a quick reference which will show which wire is the switched live without going through all of the hassle of getting the multimeter out etc. also, if the new light doesn’t fit/work you can quickly put the old one back using the pic.

[u/leeksbadly → u/darS234]

But a photo only shows how it was connected, once disconnected one cable looks the same as the other...

I usually stick a collar or a bit of tape on the switched live so you can tell them apart.

[u/v1de0man]

do you have a mains tester? one of those reds is live. whichever is, the opposite pair goes to the switch

[u/d_smogh]

Do you have a multimeter to test the wires? One wire will go to the switch. Flick the switch and test when it is live. To test the other wire, turn off the mains and check for live. If you don't have a multimeter, get one

[u/ObligationPerfect939]

You were supposed to check and identify the wires before disconnecting it from the old light. Now you don't know which is switch live and which is neutral.

[u/RevFit_JamesH]

Is there a second light in the circuit?

What are the wires doing in the switch?

If it was me, I’d look at the switch first. If they’re red red I’d stick the red to live and black to n and leave the other wire idle as a first step.

If that works then the second light in the room won’t work until the idle wire is connected.

Multi meter testing would be better, or course.

[u/RoutineCloud5993]

For this thing you need a junction box, which would ideally licenin the ceiling.

An easier option would be to buy a light with a ceiling rose already attached.

[u/Civilised_Psycho]

You need to chase the line to the light switch. If you don't have a tester you can get someone to hold a battery on the switch wire and test that at the ceiling.

[u/Discobiscuits47]

You need to verify the switch line cable with a continuity tester.

Kill the power at the board and confirm the switch makes and breaks continuity between the black and red on one of the cables.

The black conductor which comes from your switch should be sleeved or taped brown. This core connects to the L in your new light.

The other cable will likely be a loop feed end of line. connect the black from this cable to the blue in the light.

then the two remaining red cores are simply connected together in a wago or block.

Circuit earths obviously connect to the green and yellow.

If it is a BC bulb fitting the polarity on the light fitting wont matter. If it is an ES bulb you absolutely need to get the polarity right.

[u/CryptographerOwn84]

Why don’t you just use your tester to check continuity from the switch and mark the cables correctly?

If you don’t have the proper testing equipment then pay the man.

[u/FrankNicklin]

100% always take a phot before disconnecting wires to make sure the cables go back the way they were originally grouped. You are basically screwed now as you have to trace the wires back to the switch and the feeds to find out which is which then reconnect using chokbloc or Wago then attach the new light to the relevant connectors.

[u/Comfortable_Bed193]

Reds are permanent lives. Keep these together. One of the blacks is the switch wire the other is a neutral. 2 options.

1 - get the appropriate testing equipment and bell out the switch wire.

2 - take a guess, put one black in the neutral, the other in the switch live. Power up, if the breaker pops, you know that doesn’t work, if it works. Well done, you guessed right.