Hi folks
An update....
The fault exists between the CCU and the switching for the lights, which unfortunately will be done via a jb or two under the floorboards but not accessible from the holes for the lights. GRRR
In the area where I'm pretty sure this is located, floorboards have been replaced recently and screwed down, so I wonder if the fault could be a screw into a cable which is OK at 250V but not at 500?
Will have to take up the carpet/boards to investigate further.
The 'loads' ie wiring between the lights is all OK.
Thanks again for suggestions and ideas
Regards
SB
I thought you said it was the N to E that was down? This wouldn't be before the switches, it would be after the switches and on the neutral assuming lamps in place.