OOI, is there any reason I can't use the neutral incomer as an alternative to "Supplier's main earthing terminal"?
If there is a small residual voltage on the neutral, swapping the transformer phase and taking the average of two measurements would help but should be a fraction of 24V.
Yes, that's correct.
I might try that, I think I have a 24v transformer somewhere.
However, what do you think about this idea for getting a more accurate Ze measurement? My loop tester has an iec connector for a mains input - a type I have plenty of - and no other leads. I get a spare lead and chop the plug off, strip the insulation back and fit a crop clip to the earth lead and a probe to the live lead.
With the supply turned off at the CU and the earth input disconnected I then connect the croc clip to the (disconnected) earth and the probe to the input side of the main switch. Would this give me a true Ze reading, or is my thinking incorrect (would I need to connect the neutral as well?)?
I would not fancy it ;-) Remember neutral is a "live" wire - it could be several volts[1] away from local earth, and can supply reasonably significant current in some circumstances.
[1] Or possibly more depending on the load being applied to it locally (by yours and neighbouring properties), and distance from the substation etc.
If its anything like my old Megga LT5, then I think it uses the neutral to power itself since it has no battery. However in principle, you could lash up something to allow it to be powered, and also have a wandering earth lead for connection to your electrode.
That's what I'll do, I think, connect live and neutral to the input side of the (switched off) main switch and connect the earth lead to the disconnected external earth lead. That should give me a more accurate Ze.
Several is less than 24V. I am aware that neutral is now considered 'live' so best to take care.
Which should be taken into account if averaging in-phase power and reverse phase currents.
The resistance ought to be a fraction of the local earth-spike resistance. Either way it gives a worst case scenario of true live conductor to local earth resistance and prospective earth fault current.
Or am I wrong?
No, you will get a reading...
All in all though it seems like more hassle than using a bit of pipe stuck in the ground though!
I missed that bit of info.
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