UK 3-core switch understanding

I’m trying to wire a Fibaro Dimmer 2 into a switch box, but I’m a newbie to home electrical wiring, and was hoping to solicit some help!

The switch box in question has two switches - one controlling the lights of the bathroom, and another controlling an extractor fan (I think…). The extractor fan is not working, and we’re not keen on getting it working. I’m trying to work out what the wiring scheme inside the switch box is doing, and what steps I’d need to take to install the Dimmer 2, just controlling the lights.

Here’s a picture of the switch

image url

On the left is the light switch, on the right, the extractor. There are 2, 3-core (+ earth) cables coming in from the wall. On the left, the brown from the lighting wall cable connects to the top of the left switch, and the grey (with brown tape) connects to the bottom. I’m assuming this grey is the load wire to the light, which will become live one the switch has been pressed. There is an identical setup on the right switch.

The two things that are puzzling me are: the brown connector wire between the top of both switches. I’m guessing this is something to do with turning the extractor on when the light comes on, but can’t quite figure it out. The other is the two black wires from the two respective wall cables are connected together - not sure what purpose that serves here.

Would really appreciate the help!


Hmm… brown-black-grey isn’t standard for single phase wiring in the UK. You’re right in that the brown should be live and grey is the returning live back to the light.

I assume the black is neutral and both the browns and blacks are linked for the ring. This normally happens in the light though. Linking the browns together is nothing to do with keeping your fan running.

If you have a multimeter you’ll be able to test this fir yourself to make sure before you change anything.

Wiring in the Fibaro should be straightforward given live, neutral and switch wires. You’ll need a deeper back box to fit it in though.

Tagging @anon36505037

Thank you so much for the replies.

sipuncher: Going to try and diagram the circuit as I think it is put together. Unfortunately I’m not sure how to use a multimeter or what I’d be looking for. On your other point, yup, bought a new deeper back box and fitted it yesterday.

deleted: It’s not one light fitting, but four - which I’d guess would mean I’d have to root around and find the junction box in the attic. Not the end of the world, particularly if the wiring up there is a bit more standard.

Here’s my amateur attempt at trying to understand what’s going on here. I’ve left off earth as it doesn’t seem relevant. I think I’m missing why the browns and blacks are linked “for the ring” as sipuncher commented - I’m guessing its because this circuit diagram is wrong, and the ring continues to other fixtures?