Paul,
I've come across this before with Ring style distribution mains.
We use what is known as a Low Ohms Meter, it measures between 000.1000Ohms and 1 Ohm.
It is important with Power Systems earthing.
I would also tend to back up what Wolfgang is saying.
The closer the transformer, the higher the fault current.
I've seen switch-boards blown to bits, through MCB's that can't handle the fault current.
Any of you guys ever used BKM Breakers?.
IMO Don't!!.
