[SteveBayshore]

Sorry for the delay, and now I found the thread closed. My instruments were out for calibration. The top unit, a four point ground resistance tester, can be used to develop soil resistivity tests also. With that information, and the available area, a manufacturer (Erico or Harger) can design a grounding electrode system. The bottom unit, a ground tester, can direct read grounding electrode resistance. The two meters and necessary test leads are worth about $4k. Are these what you use?

 

[Big John]

I used that same model 4500, but I've never bothered much with the second clamp-on version; I've never found an application where I trusted the results because they usually vary wildly from the readings I'll get doing a fall-of-potential.

I was talking about it in this thread, I'm trying to re-invent the wheel and am looking into doing star-delta tests (which are versions of IEEE three-point tests) and what's called the "selective method" which might be doable with the neutral attached.

 

[EB Electric]

We used an earth ground clamp meter on this one commissioning job to test drops from the lightning system going down to the ground grid. http://www.myflukestore.com/p4196/fluke_1630.phpThis engineer was floored by the tester, he questioned the thing for over an hour. He couldn't understand how it works and was making us try it on loops of wire, a single strand, all sorts of stuff to try and disprove the tester. It got to the point the engineer's frequent little tests were getting so annoying one of the site foreman's pulled up a youtube video explaining how it works just so the guy would shut up! This same engineer also wanted us to open up all the floor covers, go in, and verify the connections to the ground grid... meanwhile it was all live 13.8 kV in the pit. Meeting adjourned!

 

[Big John]

...He couldn't understand how it works and was making us try it on loops of wire, a single strand, all sorts of stuff to try and disprove the tester....

I'm interested that it didn't. In my experience, it absolutely does. The most common error I get with that is an abnormally low reading, because it's going through a parallel path.

Just for giggles, I just grabbed a loop of #4 and measured 0.056Ω with a clamp on ground meter and 0.0019Ω with DLRO. I also tried with an 87V with the test lead resistance nulled out and got 0.001Ω

I don't know how that error rate translates to other setups, but that's pretty significant.

 

[brian john]

The 4500 can be utilized as a
4-point, as noted
3-point (for testing existing or new electrode when the electrode is isolated) and the test is performed per the instructions
and as a 2-point but I find this method questionable.

Utilizing the clamp on tester is not an approved NETA test and in my experience most electricians mis-use the device.

 

[SteveBayshore]

I was at an MSHA seminar a couple of years ago and was informed that the clamp-on was an acceptable method but all of the MSHA sites that we work on have multiple electrode grids and the clamp-on is not recommended for those scenarios.

 

[PolarBear24V]

glad I found this post before it was closed.

I came across a crew testing the Fall Of Potential. The equipment I came across was a AEMC 4620. I had to investigate because it looked like a mini bumble bee. lol. I found it very interesting!! But i didn't get much time to chat with the guys. So I have a few questions....

-Does most EC's do these tests? Or does another company? This was not the EC doing the test. I would think the EC would, to save $$$.
-Can a FOP test be done if everything is welded?
-Why isn't NEC 25 ohms good enough?
-Is it good to test during when it is raining?
-How much damage can be done with stuff underground while testing?

Very interesting testing.....I would like to know more!!! thank you Google...:thumbsup:

 

[360max]

...all these test, has anyone ever lifted a 15 or 20 year old ground rod and examined its condition?

 

[Pete m.]

...all these test, has anyone ever lifted a 15 or 20 year old ground rod and examined its condition?

Around these parts you would be lucky to pull up slightly more than the acorn.

Pete

 

[RIVETER]

...all these test, has anyone ever lifted a 15 or 20 year old ground rod and examined its condition?

Not me, but if I were to guess, if the rod were properly installed and then deteriorated over time in the soil, the soil would be ionized and could still work if needed as long as the connection above ground was FAST. IMO. Rods, and their effect don't just disappear.