Hi all. Changing a CU in an ex-council flat, pme system, no RCD's, and initially tried to IR test whole board L/N joined to earth, got a reading of 0.28 Ohms.
Then did each circuit individually (2 X RFC, 2 X lights, 1 X cooker), L/N joined to the circuit's CPC, and got between 0.25 and 0.30...