Electrical Problem

[darbo1103]

RCD trips when I replace the fuse for the downstairs lights. All other electrics work, but not the lights.
Can anyone also advise how to wire a 2 way switch? I have 2 red wires, 2 black wires and 2 earths which are together in a terminal block. There is also a red wire going from common to common. Old wiring I'm afraid.

[Iggle Piggle]

Agree with Methyl. This is not a fault you want to be playing with, it needs a qualified sparky. If you have old wiring, the insulation may be cracking and the whole house might need re-wiring. Bite the bullet and get someone in.

[darbo1103]

Thanks for the advice, it's appreciated. I don't intend to try to fix the problem, I'm just curious why it's happened and how the switch is wired. There were no problems at the start of the day, but since removing the face plate to plaster, there's been an issue. I will be getting a qualified spark in to check a this is far, far beyond my limited knowledge.

[The Builder]

Agree with the others there Darbo. There's likely an earth fault in the lighting. (Live to earth). Possibly why the RCD operates when the circuit is re-energised.

2 way switches are not complicated. It's just that they usually involve 3 switch wires, not 4. There'll be a simple reason for your set up. An electrician would be able to suss it out in no time.

[darbo1103]

Thanks again..Got a qualified electrician in to check things out. He checked the switch, couldn't see anything immediately wrong. Power off, fuses in, trip, power off fuses out. Checked ceiling rose (something which hasn't been touched for years), moved wires about, fuse back in, power on, NO TRIP!!! Checked the wiring and said in 30 years of working as an electrician, he had not seen a ceiling rose wired in such a way. Got it working anyway, so problem solved.