Testing 25 ohms to ground

[MasonF]

Hi on a grounding electrode rod commonly adjacent ti residential breaker panels, what is the name of the tool which can test resistance between Earth and ground rod And how is it done?

NEC Allows exemption of one electrode conductor is resistance is “25 ohms or less?”

Thanks

Also to the best of my memory I calculated grounding conductor to be 6 AWG based (Or 8???) on Largest conductor (feeder?) being less than 1/0

Is this right. Thanks

To answer the second part of your question 250.66(A) says that you dont ever have to have larger than a 6awg copper grounding electrode conductor. Youd have to look at table 250.66 to see if you could go smaller.

 

[Fred B]

Are there any studies or papers on what ground resistance for typical one or two ground rod systems might be?

It would probably be drastically different from state to state.

And day to day depending on weather, soil moisture, ground freeze depth (winters), soil type, etc.

 

[jim dungar]

I've had to relocate a ground rod or two because I could literally pull the entire rod out by hand.

That sounds like an issue between you and your AHJ. I can not find any NEC reference saying sand needs to be treated any different than "plain dirt".

 

[Jpflex]

To answer the second part of your question 250.66(A) says that you dont ever have to have larger than a 6awg copper grounding electrode conductor. Youd have to look at table 250.66 to see if you could go smaller.

Isn’t that 6 awg limit only applicable to supplemental electrode, but not main grounding electrode?

 

[roger]

Isn’t that 6 awg limit only applicable to supplemental electrode, but not main grounding electrode?

No, as pointed out read 250.66(A) and think of a rod or rods being the only electrode.