Two gang switch removed and replaced but now trips RCD

[surf_doc]

Hi,

A couple of days ago I bought a new two gang light switch as a replacement for a slightly tatty hall switch.

The old item was wired L1 (brown), L2 (grey), L3 (black) for both switches, as you would expect. The new switch is of the L1, L2, COM type. So I wired L1 live into COM, L2 into L1, and L3 into L2 for both switches of the new unit.

I tested it and it immediately tripped the RCD.

Despite being confident that I had wired everything up correctly, I decided to put the old switch back in today in place of the new one so that we at least have working downstairs lights. So I rewired the old switch to be exactly as it was before, and ... the old switch is now tripping the RCD.

For reference, this two gang switch controls a downstairs hall light (R switch) and a middle floor hall light (L switch).

The downstairs hall light can be turned on and off also via a second switch by the front door, which I have not touched.

If I turn this downstairs light on now via either the door switch or the old switch I put back in, it will trip the RCD for both the downstairs group of fuses and also the RCD for the upstairs group of fuses (this group includes the upstairs lighting ring).

I have removed the bulb from the downstairs hall light and still the same thing happens.

Can anyone suggest what I could try next to resolve the matter? Any/all ideas appreciated.

Obviously, I could just call an electrician but if it's something straightforward that I have somehow missed then I would like to avoid that cost.

I have attached a picture of the two-way switch wiring.

Thanks in advance.

 

[bernardgreen]

The three wires to the purple switch must come from one of the cables and the three wires to the blue switch must come from the other cable.

 

[surf_doc]

Thanks for the reply.

Yes I am wondering now if that is the issue - it seems the most likely.

All six wires come out of a small hole in the corner of the switch recess and it's virtually impossible to tell which go with which. I thought I had got it right but the evidence suggests otherwise.

I will tag the individual wires tomorrow and get the right configuration through testing.

Thanks again.