almost completed a rewire. about to do bonding and earthing tomorrow. looking at the existing arrangements, the MET in the old DB has a black cable, roughly equiv to 10mm disappearing up under the bathroom floor above the DB. on the outside of the building , theoverhead incoming enters a box about 8" square. i am wondering if it's TN in this box. obviously i don't want to interfere with the box if i can help it. first thing tomorrow, will see if i can get a Ze reading, otherwise have to TT it. anybody come across anything like this before. the original install is 1950's , but the incoming supply seems to be later .
