1. Yep a centre zero meter, I have a look if i can locate the circuit somewhere and will post it when found
So you can cancel out stray currents which are always in the ground.
AC is of no use because of return currents with the M.E.N. system used in New Zealand. I thought it may be because of stray currents. But if his cable is remote from power sources, eg. on a farm, would there be any stray currents?
2. We use 2 spikes to probe in the ground, say 2 metres apart and walk the direction of the cable.
Where the pulsing DC leaks out where the fault is, the microammeter will pick that up by means of the deflection of the needle it is pulsing, and so a very accurate locate can be done. Can you only read the current near the fault? Or is it readable all along the cable until you pass the fault?
3. Reason as above. If continuous dc you are unable to pick up the readings.
But if remote as I wrote above, would DC work?
In our POCO we use a 240 to 4200 Volts supply step up transformator which is controlled via a variac, then a voltage doubler with smoothing capacitor which will get voltage up to 10 kV dc for burning in a high resistance fault.
Then flick it over to pulsing DC via a on off timer and you are in business.
240+V sounds dangerous. I hope he does not electrocute himself.
You probably get away with lower test voltages but I use this set up to pre locate 11 kV and 33 kV faults as well.