I'm trying to change a UK light ceiling rose in a 1920-30's house and after taking the old rose cover off, the wiring has thrown me. It looks like there's 3 of each live, neutral and earth, and some odd colour choices on the wires. This is the only fitting in the room and is controlled by a single switch. The new rose seems to only need 2 of each wire. Any advice, or is this rose simply not compatible with my wiring?
You have neutral, live and a switch loop (in addition to ground). Plus a daisy chain to the next light in the circuit in another room.
The neutral block with all the blues has all the neutrals that come from the supply and go to the light and the next light.
The live block with the 3 browns has the live from the supply, has a connection to the next light and to the switch.
The last block with the brown sleeved blue and brown is the connection between the switched live from the switch to the live of the light.
If possible I would suggest keeping the existing electrical connections in place and use them to connect to the new light.
Otherwise check if the terminal block allows for 2 wires into one side of it. That will let you connect together the 3 wires.
If not then your local DIY store should have 3-way wago blocks that you can use instead.
I'm trying to change a UK light ceiling rose
The UK ceiling rose is possibly the most elegant junction box in the world. It has exactly the right terminals for any of three different applications. The entire point is so you don't have to disturb all that when you change a lamp.
It looks like there's 3 of each live, neutral and earth, and some odd colour choices on the wires.
Plus the lamp itself, so four, really. That's completely normal wiring for lamp ceiling roses. Ceiling wiring is not designed for the convenience of novices installing their first light fixture. The novice must skill up in order to "play". Now this isn't a code requirement in the UK, but I myself would mark the top two wires (the blue-marked-brown and companion brown) with a distinctive color like orange, since those are switch-loop wires, energized only when the light is to be on.
The new rose seems to only need 2 of each wire.
And did this come from a reputable retail shop? A great deal of stuff which BSI (safety certifier) would most emphatically say is "not for your country", is sold via mail-order, particularly Amazon Marketplace (Amazon, but the "Sold By" is not Amazon).
Any advice, or is this rose simply not compatible with my wiring?
I would not disturb the rose at all. After turning the mains off, I would cut the lamp cord about 150mm (6 inches) from the rose. Et Voilà, the three wires you are seeking. It should be easy work from there - no need to decrypt the magnificent British ceiling rose. Then you have a lumpy splice; hide that behind the new lamp's dome.
As others have said, I wouldn't replace the ceiling rose, since any replacement is going to need the same number of connections (and if you get it wrong, other lights will stop working).
So what I'd do is remove the terminal block from the new light fitting, leaving the 3 wires (line, neutral, earth/CPC). At the rose, undo the brown and blue wires from the existing pendant and replace with the brown and blue from the new fitting. It looks like the existing pendant has no earth connection, so you'll either have to find space in the earth terminal for the new fitting's additional wire, or add a small 2-into-1 connector (eg 3-way Wago 221) to tee it into the earth connection.