I've tried changing the lighting in a room and I found a set of wires that I don't know to to connect in order to have a live, neutral and earth. Can anyone explain?
Firstly, note that the three groups of wires are effectively bundled by their respective brass contact sets (buses) and kept in isolation.
Based on my understanding of U.K. wiring convention...
- Red is hot (live). Likely one comes in and two go out to switches and other circuit branches. In your case, the red next to the yellow may be outbound to the switch.
- Blue is neutral. It appears connected to black neutrals, which are common in older wiring.
- Yellow is probably the return hot from the switch.
- Yellow/green is ground (earth). The existing light doesn't appear to be grounded. This is common as many fixtures are "double insulated" and don't require ground. If your new fixture has a ground wire it should be connected to that screw.
Therefore, by connecting a new light fixture as this one is, you'll have neutral to neutral and hot to switched hot.
You'd be wise to own and use a multimeter to confirm all this.
Your old fitting is a standard UK ceiling rose with connector groups for earth, neutral, loop (live in), and light (switched live). Your new fitting has only got three terminals: live, earth, and neutral. In order to replace the rose with the new fitting, you MUST fit a new junction box above the ceiling.
It looks like you have 3 cables coming into that rose. 2 are 2-core+earth (read and black). These will be power in (from the consumer unit) and out (to other fittings on the same circuit). There is also a 3-core+earth cable (red, blue, yellow). This will be the switch cable.
You will need a new piece of 2-core+earth to go from the new junction box to the new fitting. This will have brown and blue wires in it.
In the junction box, the connections are as follows:
- All bare wires (earth)
- All 3 red wires (live)
- both black wires and both blue wires
- yellow wire and brown wire
In the light fitting, the new brown connects to the L terminal, the new blue to N, and the bare to the earth symbol.
The 5A lighting junction boxes can be difficult to use properly. It is very easy to lose the terminal screws or to fit them badly and damage the terminals. If you are at all nervous about this, get a professional in.
The ground (middle) terminal on the new light should be connected to the spare ground terminal on the left side of the ceiling box with a new piece of yellow/green wire.
Disconnect the brown and blue wires from the old fixture in your hand. If they are not removable, cut them as close to the old fixture as possible. Connect them to the empty terminals on the new one. Brown to L and blue to N.
Pay attention to the routing of the blue and ground wires through the strain relief studs. Do that.
The old fixture looks like it's threaded and screws onto the ceiling rose. The new one looks like it wants a couple of screws sticking out the sides to hang on. I'm not sure what the solution is to that. You may have to replace the whole ceiling rose. Probably a job for an electrician if you're not comfortable with it. Start by taking the light to an electrical supply store and buying an appropriate ceiling attachment.