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I have no idea what that was, but it's hard to imagine he was measuring resistance with an inductive meter.  I suspect he was measuring current and if he's getting a resistance reading, it's probably deduced from the current reading.

 

Here's a page on Ground Testing Techniques, sounds like a variation of what I was thinking.  They induce a current into the ground with one winding and then measures the current.  Here's a quote from the article.

 

The jaws of a clamp-on tester contain two windings. When clamped over a ground rod and energized, a CT in the tester induces a test current in the circuit via electromagnetic coupling. The current travels through the soil and returns to the rod (but more significantly the jaws of the tester), thus completing the circuit through all available system grounds. Since multiple parallel utility grounds, for instance, are normally plentiful, their total resistance is negligible, and the test measures principally the resistance of the intervening soil. The tester accurately measures the current flow, and the second winding in the jaws sense the voltage drop around the loop. Ohm's Law does the rest.

Thanks, john.  The clamp was much wider than normally see on a clamp-on ammeter.  Mucking around on the internet, I came up with this:

 

http://www.amazon.com/Reed-MS2...ohm+resistance+meter

 

It's a bit more than I would spend on an ohmmeter, and it's hard to see how it can be accurate.  It reads the current it is creating???????

 

I also found a Fluke meter which runs a few hundred dollars more.  The Fluke description says:

  • The clamp-on ground testing technique used by the Fluke 1630 simplifies ground loop testing and enables non-intrusive leakage current measurement. The compact and rugged design makes the Fluke 1630 easy to use in small places and harsh environments, while the ‘display hold’ and the continuity testing with an audible alarm function ensures convenience in use. The novel technique means that earth ground loop testing and continuity testing can be completed without breaking the circuit.

    Stakeless testing system

    The Fluke 1630 uses the Stakeless testing method, which eliminates the need to disconnect parallel ground rods and find suitable locations for placing auxiliary ground stakes. This saves time and enables users such as industrial and utility electricians, and field service electricians and contractors, to perform earth ground loop tests in locations where it is not possible to use other techniques, including inside buildings or on power pylons. With the Stakeless testing method, earth ground stakes are no longer necessary. The Fluke 1630 Earth Ground Clamp is placed around the earth ground rod or the connecting cable. A known voltage is induced by one half of the clamp and the current is measured by the other half. The tester automatically determines the ground loop resistance at this grounding connection.

 

There's a lot of info on the Fluke web site.

 

I figured someone out there in Forumland would have knowledge of these gadgets

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