This one seems like it covers all bases.

 

All I know is I've never seen any serious PQ survey done with the clamp-on AEMC meter.

Everyone does fall-of-potential with something like the device in your second video, and it requires placing auxiliary leads dozens of feet apart.

-John

 

All I know is I've never seen any serious PQ survey done with the clamp-on AEMC meter.

Everyone does fall-of-potential with something like the device in your second video, and it requires placing auxiliary leads dozens of feet apart.

-John

Ok, but how would you just test an 8' GR for resistance ? I've heard about inspectors checking to see if you've cut the rod.

 

Typically the average electrical contractor subs this out for several reasons, equipment, training and 3rd party testing normally spec’d.

For what it cost to sub this test it is well worth it.

 

The piece of copper is 25 ohms right ? (uncut) so if someone cut the rod short because of rock, how would the inspector measure to see that it is not 25 ohms ?

 

The copper rod itself should be much less than 25 ohms. The "25 ohms" is the resistance measured between the rod and some part of the earth.

I don't know how clamp-on meters work, I'm thinking they must induce a signal and then measure the return somehow, but if they're designed to measure resistance to earth, I don't see how it would know the length of the rod:

It's possible for a long rod in very highly resistive soil to give a poor reading. Also possible for a short rod in wet soil to give a great reading. How would the meter know which part of that resistance was from the copper, and which part from the soil?

-John

 

I have had DSA inspectors test my rod installation on a few occasions. They always used the "Biddle Earth Resistance Tester" if it's not 8 ohms or lower, I was told to drive another rod within 6 feet or relocate rod. Then he checks again when I am ready. I found that pre soaking the soil always produces a passed test. I bought my own Biddle tester (same model DSA uses) so I know it will pass first time. Only because I found one cheap enough. It has 3 leads w/clips of different lengths and two grnd spikes. short lead on rod, medium lead on spike, long lead on further spike.

 

I have had DSA inspectors test my rod installation on a few occasions. They always used the "Biddle Earth Resistance Tester" if it's not 8 ohms or lower, I was told to drive another rod within 6 feet or relocate rod. Then he checks again when I am ready. I found that pre soaking the soil always produces a passed test. I bought my own Biddle tester (same model DSA uses) so I know it will pass first time. Only because I found one cheap enough. It has 3 leads w/clips of different lengths and two grnd spikes. short lead on rod, medium lead on spike, long lead on further spike.

Isn't presoaking the soil cheating ? How long does it take to perform the test ?

 

Back in the day, A ground rod was tested with a fused switch and a little knowledge of ohm's law.

If the fuse blew, the ground was good

 

but, doesn't earth R change with seasons & ph ?

my garden sure does....

~CS~

 

Freeze, drought, heat, excessive rain, lots of things all but a tsunami, because after a tsunami who cares.

Yes and with depth and distance. But in testing you are establishing a bench mark.

As for testing electrodes I/we have tested 100’s of sites and testing electrodes in more involved than a 5 minute test to get accurate (as accurate as possible) reliable, meaningful, NETA acceptable results.

As for adding water or testing within 48 hours of a rain (standard spec), this is IMO fairly worthless to a test properly performed. By going out a minimum of 10 times the length of the single electrode or 10 times the diagonal of the grid you are supposedly testing the effective resistance of the full length of the electrode and the area around this electrode, not just the top 2-4 inches for a 24 inch diameter, which short of soaking the ground with a hose for hours and hours is about all you can hope to gain by a bucket of water.

 

Read the following About 3/4's of the way through this piece (page 19 and on). Aditionally we do a minimum of 3 complete test.

Ground System Testing
Fall of Potential Method​

http://www.lyncole.com/uploads/Lyncole_Ground_Test_Methods.pdf