Changing light fitting with red/black uk wiring

light-fixture

I have attempted to replace my bathroom light fitting. It has 2 red wires and 2 black. In the original standard light fitting, it has one black in the live and one in neutral. Then the two red loop wires were in the middle fitting see photo:

Now see below photo of the new light fitting. It worked when one of each the black and red were in both the neutral and live. But when I turned the light off, the electric trips, and won't come back on. What am I doing wrong? Note the naked wires are earth.

Best Answer

It worked when one of each the black and red were in both the neutral and live. But when I turned the light off, the electric trips, and won't come back on. What am I doing wrong?

It sounds like you have wired the switch across the light. When you "turned off" the switch you were actually turning it on and creating a short circuit.

The two red wires need to connect to each other, but not to the light fitting. Traditional UK ceiling roses had a dedicated terminal for this, but sadly most fancy fittings don't, so you have to add your own connector. The tranditional option in the UK would have been a peice of terminal block, but push-in or lever connectors from the likes of wago are increasingly becoming a popular alternative. Personally i'm a fan of the wago lever terminals.

The black wire from the switch should be sleeved red or brown and connected to the live terminal on the light, while the black wire from the supply should be connected to the neutral terminal on the light.

There are various ways to determine which is the supply cable and which is the switch cable, but I suspect the easiest for you is to connect the cables to the light one at a time while capping off the other cable temporerally with terminal block or wagos. Then turn the power on and if the light comes on you have the supply cable.

Related Solutions

Wiring – Replacing light fixture UK unable to determine which wire is which

One of those cables goes to a switch loop. You need to find out which. Open up the switch that controls this light and see what wire colours it has.

If the brown and blue (new colours) are the switch then connect

red to brown (which takes live to the switch)
blue to the "L" terminal of the the light - blue is switched live so you must put red tape around the blue wire.
black to the "N" terminal of the light (neutral)
put a green/yellow sleeve over the bare earth wires and connect them using an approved connector. If the lamp has metal parts, they need to be connected to these earths too. The middle terminal in your second photo would probably be intended for this. Check for continuity between all metal parts and the earth wires.

UK Wiring colours

              Old       New
 Live         Red       Brown
 Neutral      Black     Blue

Electrical – New light fixture to old wiring

You hook the new lamp exactly the way you found the old lamp

All the white wires from the old lamp went to one place. That place is where the white wire goes for the new lamp.

All the black, red and/or blue wires from the old lamp went to one place. That is where the new lamp's black wire goes.

You don't mess with anything else.

Particularly, you do not group wires by color code if they weren't before. Color codes do not have the purpose you wish they did, they don't tell which wires go together or what the wires do. Cable colors are part of manufacturing the multi-wire cables, because making all the wires the same color wouldn't work.

When you see wires bundled together, those wires are not "spares". They are already engaged in other tasks and need to stay the way you found them.

If both blue and red wires went only to different wires on the old lamp, then pick one and cap the other.
It's not unusual for there to be no grounding wire in old fixtures. Don't "island" a ground by attaching it to something, what you did was fine.

Oh. You messed with anything else.

Well, the good news is, given the blue wire and combinations you stated in your comment, this work is plainly in conduit, so there's a fair chance the wire colors are in fact meaningful. What a refreshing change, Usually they don't mean much.

The ground will automatically get picked up via the mounting screws when you mount up the harp. (This "via the screw" method only works on lamps and switches, not receptacles). So grounds are no worry, I love metal conduit.

The whites look OK, with one remotely possible, critical exception.

Based on what you say it's the blue wire. They were kind enough to color code the wires and it looks like blue, being a solo, is for this light.

You could also try the red, but Ihave a feeling that's for the fan.

Beyond that you are going to need to bring in a pro. Do not just repeatedly experiment. You are likely to discover combinations which do what you want, but that create a dangerous situation.