Fault finding today Lighting circuit burnt through at 8 x places, isolate at the midpoint with faults both sides, split circuit into 6 individual sections and all showed a dead short between these conductors. Mains details PME system with a 5A type 1 MCB in the consumer unit -: An inspection in the roof revealed the wiring passing through the loft insulation had completely burnt through, with no visible insulation on the wiring. 3 hours and many checks later the cause was found to be an over heating neutral conductor at the cut-out. The neutral current, which could have been around 65A returning via a neutral to earth fault on this lighting circuit. Any stories your end of open circuit PME systems
Had very similar in a building split into two properties. Lighting circuit fuse blown, insulation resistance flat down. Starting splitting circuit as you do, splitting L and N but leaving earths connected. Each section showed faults. Disconnected one length of cable with the intention of pulling through a new one (no access above). As I disconnected the earth, it sparked like hell. The neutral to this property was lost, and as it had been poorly split from the other half which had a new supply, the earths on the lighting circuit where still common. The installations current was flowing back down the earth of the lighting circuit, to the neighbouring property, through their earths and to their cutout. Nasty.