Hello went back to job today and checked insulation res test had a N/E fault on the lighting cct . Then tested rcd at the board and it tripped with the cct disconnected. stripped down the cct and found nothing wrong. the odd thing was ,i took out all the neutral's and had a dead short between neutral and earth i then switch of the main isolator and the dead short went its on the incoming main when i spoke with the supplier i was told it could be that the joint in the road is n/e combined and the strip a earth out of the joint and bury it in the ground ,he thinks i was picking it up via the earth rod .

strangely when i put the lighting cct back i rechecked the rcd tripping  time the left rcd now trip's could it bee then led lights that is causing it not to trip its a a A type rcd   

Hello went back to job today and checked insulation res test had a N/E fault on the lighting cct . Then tested rcd at the board and it tripped with the cct disconnected. stripped down the cct and found nothing wrong. the odd thing was ,i took out all the neutral's and had a dead short between neutral and earth i then switch of the main isolator and the dead short went its on the incoming main when i spoke with the supplier i was told it could be that the joint in the road is n/e combined and the strip a earth out of the joint and bury it in the ground ,he thinks i was picking it up via the earth rod .

strangely when i put the lighting cct back i rechecked the rcd tripping  time the left rcd now trip's could it bee then led lights that is causing it not to trip its a a A type rcd   

Afraid that is making no sense at all. If the supply is "n/e combined" it is TN-C-S (PME). So my first question is what is the earthing arrangement?

Is there PME next door ? Are the services metal . Could be connected through the bonding. The rcd's need testing before anything else is connected to them to eliminate faulty rcds then go from there.

Gary