Light circuit tripping RCD

[the_upsetter]

After a bit of help on how to proceed:

Part of my downstairs lighting circuit is tripping the RCD so I've disconnected the live/ brown wire for this circuit from the MCB and this leaves the rest of my downstairs lighting ok.

What should I be looking at to resolve? I have disconnected exterior light feeds from within by disconnecting live / neutral / earth from the internal switches but still the RCD trips when the remaining circuit is connected back up.

 

[sparkwright]

So I take it there were two or more live wires at the MCB?

 

[sparkwright]

Drilled through cables.

Stray wires or trapped wires behind fittings.

Wire 'pinched' to fixing screw/lug at light switch.

Mice.

 

[sparkwright]

Had you done any electrical work before it started tripping?

 

[the_upsetter]

Had you done any electrical work before it started tripping?

No work has been carried out since the new consumer unit was fitted last year, the MCB was feeding three wires and is now feeding two.
There was a drink spilled on the landing a few days ago and the RCD tripped yesterday. I haven't seen under the landing floor for a few years but remember a number of junction boxes below. Should I give it a few more days to dry out before checking my bank balance?

 

[sparkwright]

Mixing up the neutrals during a consaumer unit change can cause such a fault, BUT SINCE THIS WAS LAST YEAR IT WOULD HAVE BEEN NOTICED IMMEDIATELY, AND NOT YESTERDAY.

A drink over a junction box could cause tripping, though I'm not sure if one drink would be enough to go through the carpet (if you have one), then the floorboards, then into a junction box. Seems unlikely, but anything is possible.

The fact you have only removed the live wire to stop the tripping suggests a live-earth fault or a live-neutral fault, rather than a neutral-earth fault.

 

[the_upsetter]

Mixing up the neutrals during a consaumer unit change can cause such a fault, BUT SINCE THIS WAS LAST YEAR IT WOULD HAVE BEEN NOTICED IMMEDIATELY, AND NOT YESTERDAY.

A drink over a junction box could cause tripping, though I'm not sure if one drink would be enough to go through the carpet (if you have one), then the floorboards, then into a junction box. Seems unlikely, but anything is possible.

The fact you have only removed the live wire to stop the tripping suggests a live-earth fault or a live-neutral fault, rather than a neutral-earth fault.

Thank you for your help, I'll borrow a megger tomorrow to try to work out the fault from that. The drink was spilt over carpet /underlay / floorboards so I agree it's unlikely.

 

[crystal ball]

I had a job last year looking for a L-E fault, it turned out to be a leaky pipe dripping on a JB, it was on bare floorboards though in the airing cupboard