Ground Testers

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SEO said:
Has anybody any experience with the clamp-on earth/ground resistance testers? Are they accurate ?
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More accurate readings can be obtained by other testing means, but they're "good enough" for most things. I consider it to be a quick and dirty test.
 
If used properly and on the right type of system they can be very accurate, (See attached study) but they have limitations and are used incorrectly by about 90% of the people that use them.

Common mistakes:

It can be connected to a ground loop rather than a lead to a grounding electrode. It will invariably provide a very low resistance for the ground loop which has no relevance to the actual ground resistance.

A clamp-on cannot test an isolated ground. There is no return path in place to complete the test circuit.

Because the clamp-on measures an entire electrical loop in series, the clamp-on experiences some loss of accuracy at the critical low end where the best grounds are established.

There are many other misapplications, basially you should always do a fall of potential test because when done correctly is does a self check (Plauteau region check)
 
Thanks for the info. We use the three point fall of potential test as well. I thought if the clamp on worked well I might invest in one. They are to expensive of a meter to buy and not get accurate readings.
 
Thanks again Brian. Most of our testing is is in gravel pits, testing ground rods for electrical services. I thought that a clamp on might give a quick accruate test. It is usually very dry and it's also sandy.
 
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