Troubleshooting RCD Tripping

[madboater]

I have been called over to my mother in laws as here electrics were out.
Here consumer unit appears to have two banks of trip switches, each bank has its own RCD, then the master isolator switch.
It was the RCD from one of the banks that had tripped, with all the individual circuit trips remaining "up". I switched off each circuit and could reset the RCD until I turned the lighting circuit on when it tripped again.
Further investigation on the lights showed that I could re-engage the RCD if I put the lights in the loft on (two strip lights) then I can set the RCD. however when I turn the lights off, the RCD trips again.
I have limited diagnostic tools (I have used a plug socket tester in all the plug sockets) can anyone suggest where I should be paying attention and what to look for?

A few other pieces of information that may or may not be relevant;

• The last time Electrical Work was undertaken on the property was back in August when a new boiler was fitted. Before that was June when a smart meter was added.
• The issue occurred as the council were replacing the street lamps, it was originally assumed (by my Wife and MIL) that they had cut the power to perform the work.
• My MIL was in the loft today, were there are plenty of cables clipped to the walls/rafters, I suspect one has been damaged somewhere.

Thanks in advance.

 

[ericmark]

Is it two way lighting? I would be looking for rodent damage.

 

[madboater]

Hi, thanks for responding. It is not a two way switch, but have started to look for vermin. My gut was telling me it was a damaged cable, but it's a nightmare trying to follow the runs. Any idea on a suitable test device?

 

[Taylortwocities]

Any idea on a suitable test device?

One of THESE
or maybe
One of THESE

Untitled

• Taylortwocities
• 4 Sep 2011
• 2

 

[deadshort]

I would disconnect the lights in the loft at each fitting and make safe. This will eliminate the fittings being the cause if the circuit trips.

DS

 

[Luckyphil]

If they are Metal fittings it could be that the Fittings are damp , they get pretty chilly up there at this time of year , Maybe swap them for Pendants and try that ??

 

[333rocky333]

Bit of a wild quess, but are they old fittings, older fittings tended to have large capacitors inside, usually across the supply for PFC and sometimes with twin fittings one to stop strobing.
Dont know why exactly, but have heard of these tripping rcds, when powered both "off and on"