Had a problem the other day. Customer said lighting tripped at irregular intervals. Found main lighting supply went straight up to top floor(three floors) and along under floor to (when i eventually found it)a string of four junction boxes daisy chained with three cables from each. After a day of searching problem was found to be a light fitting with a bit of water damage causing neutral/earth fault. I must have found twelve jb's in all, all hidden under floor. Customer said place was rewired eight years ago. Cables were a mix of white and grey. Not one loop in.