Clamp On Ground Resistance Testers

[joan271273]

Can some advise experience with Clamp On ground testers as means to determine a system ground resistance value. Electrical distribution cannot be turned off therefore the use of the clamp on unit.

 

[peterb]

Check this link:

http://www.aemc.com

I haven't actually used these testers, but did evaluate them a couple of years ago for possible utility use (they decided against proceeding at that time).
I suggest, as with any unfamiliar technology, that you discuss a validation/evaluation program with the manufacturer - get hold of an evaluation unit & set up appropriate field tests against standard instruments.

 

[jbartos]

Suggestion: Visit

http://www.meter-china.com/clamp meters.htm

http://www.alfaelectronics.com/

http://www.beha.com/beha/main.asp?language=uk

etc. for more info

 

[busbar]

In the evaluation, consider that clamp-on instruments need 1½-2 inches of straight conductor for test. This may make hand-hole/valve-box-mounted rod tests impractical.

 

[jbartos]

Small encore: It is possible to use a suitable clamp-on ammeter and measure the current in the neutral. Then, if all parameters, except the ground resistance/impedance, are known one may determine the ground resistance or impedance.

 

[kraigb]

I have used both the clamp-on ground loop resistance testers and the 3 and 4 point ground resistance units for grounding studies, and have found a fair amount of agreement between them. Of course there are times when the readings between the two methods will diverge (such as when ground connections have significant resistance from corrosion or bad crimps, etc.). It's usually just a matter of knowing the ground circuit under test.

The 3 and 4 point ground resistance testers require open earth to drive additional ground electrodes, and are designed to give you the resitivity of the earth itself, which is part of the circuit that you are measuring with the ground loop resistance tester, but you have the added benefit of being able to take the ground connection of the device under test out of the circuit for comparison purposes.

I remember a guide from Biddle called "Getting Down to Earth" (also known as Manual 25T at Biddle) that we used to use with the ground resistance testers that provided quite a bit of useful tips on measurement and mitigation of high resistance grounds. They have a nominal charge for the manual, but you might be able to sweet-talk them for a copy as well.

AVO (the parent company for Biddle) has a link on their website with some info that you might find useful.

http://www.avointl.com/products/groundtster/xtra/guides/guide.html

AEMC, the maker of the ground loop resistance tester we used, also has a manual that you can dig up online:

http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/grdbook.pdf

Hope this gives you something to work with...