Is there a simple, somewhat inexpensive tester to measure ground rod resistance? I've checked my Grainger catalog and couldn't find anything.

Yes there is a simple clamp on but not inexpensive over $2000. AEMC and EXTECH offer them.

Frank,

I think you are going to have to define inexpensive.

Watthead,

The EXTECH Clamp-on is under $1400 - we sell them here in the store.


There is another type they have that is under $200



Look here:
https://www.electrical-contractor.net/the_store/EX/GRT_Main.htm

Bill

[This message has been edited by Bill Addiss (edited 08-16-2002).]

This one goes for $113.......

Sparky,

The one that you pictured is meant to measure high resistances.

this one is more suitable for Ground Resistance testing.

Bill

Thanks for the informtion.
In general, a second ground rod is required to be driven only if the first is found to to have a resistance to ground greater than 25 ohms.
Who usually provides the resistance test, the electrical contractor or inspector?
I'm aware a lot of times the second ground rod is driven just to be done with it and not be concerned with a resistance test.

Where I am in Maine 2 ground rods are driven as a matter of course. No one(at least to my knowledge) checks resistence to ground. Drive the 2 rods and be done with it. What about checking it with a copper sulfate electrode, commonly used to check cathodic protection on underground metal tanks and piping

walrus-

That is basically how it is done in my area. I was more curious than anything else. I thought there may of been a tester somewhere out there that was physically small and in the price range of $60.00 that was made specifically for measuring the resistance to ground of a ground rod.

Frank

A copper sulfate electrode can't be that expensive? and then all you need is a 10meg ohm multimeter to check resistence. Whether or not this meets AHJ standards I have no clue. I can tell ya that soil conditions make a huge difference on how the copper sulfate elevtrode reacts.

oops, yeah it's a megger.....

Can anyone explain how these clamp-on testers work for measuring Ground rod resistance?

As far as the clamp ons go Bill, we have recently challenged their validity. Wasn't my fight, but am in the middle of the outcome. I can report what we find, but it will be awhile.

There is some condensed material at http://www.tradeport.on.ca/ApplicationNotes/aemc.pdf

The three-point or "fall-of-potential" method is probably the most commonly used.

Clip-on testers are described on pg.22 They seem to be most suited for testing single rods that are part of a multi-rod grid.

George,

What I meant was how they 'do what they do'.

BJ,

That looks like an interesting paper. I printed it out and will surely read it at first opportunity. Thanks!


Bill