water in the lighting

[stuart noble]

After an upstairs plumbing leak at my son's house the light switch in one of the downstairs rooms has stopped working. The switch itself seems ok but it doesn't turn the light off. Originally, water poured down through the ceiling rose, but nothing tripped at the time, and it has been hanging loose for a couple of weeks in the hope that it would dry out. Should I just replace the switch and the rose or can anyone pinpoint what might have happened? Thanks for any advice.

[Colin Wilson]

Other than maybe it being a 3-plate system, and the live loop is shorted to the switch return, not a clue :-}

Could the switch have welded itself together ? (i.e. does it feel like it's switching normally, or a bit askew)

[TMC]

It may be that the rose/pendant was disconnected when the leak was discovered and then re connected wrongly

If the pendant had been reconnected to the loop live and neutral rather than switched live and neutral it would behave as you describe

Tony

[stuart noble]

No, the wiring wasn't touched after the leak, other than the bulb being removed. As I said, the switch itself feels normal and, AFAIK didn't get wet in tne first place.

[TMC]

Take the switch off and disconnect either the feed or return and see if the light goes off. If it don't then its not the switch

I would do this live but that's just me

Probably best to isolate first disconnect a wire and insulate then put the power back on

Tony

[stuart noble]

Cheers. I'll try that tomorrow.

[meow2222]

Sounds like the water has created a short between live and switched live. It might be conducting through the water, or maybe as the water evaporated a conductive carbon track was created where the water went o/c.

I'd strip back the ends of the switch cable at the pendant fitting and reconnect. If the light comes on with the switch cable removed, then the rose will be faulty, and its connector strip need replacing.

NT

[stuart noble]

Thanks. In theory the fault should be in the rose because that's the bit that got flooded. Presumably if I disconnect the switch at the wall and the light stays on, I'll need a new rose. If not, I'll need a new switch. Or maybe it's not as simple as that...

[meow2222]

the fault could be in the cable end or the rose, both got flooded together. I'd disconnect the cable at the rose and test, then you'll know which is the problem. A bad cable can be cut back and reconnected.

NT

[stuart noble]

Spot on. All the connections were bone dry, but covered in salts. Wiggled the wiring and there was a bit of snap crackle and pop before the bulb blew. Fitted new pendant and all was well. Seems like the dry salts were behaving just like water. Well, I've learnt something today! Thanks for that.