Grounding Electrode System resistance to ground

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AK GUY

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juneau, AK. USA
Any Cities, Counties, or municipalities out there ever request 3rd party testing of Systems resistance to ground if ground conditions might be in question. We have some residences being built in our area where the lot is blasted out of rock, and the foundations are on shot rock. The water services are HDPE, and the footings are insulated and vapor barriered. I have a real concern about developing a grounding electrode system.
 
The requirement is that you install two rods regardless of their resistance. The NEC does not require testing. You can use one rod if your resistance is 25 ohms or less.
 
I had to install a 45 KVA Xfmr in a cave. ( Underground Storage Facility)

Ponder the Grounding Electrode system on that one for a while.:)
 
So there is no dirt whatsoever?

I think this is a case where 90.4 (second sentence) comes into play. Your Chief Building Official has to decide what to do based on local conditions.

250.53(G) seems to assume there is some dirt to above the rock. In your case with no dirt above the rock, you have a case that is not contemplated by the NEC. IMO
 
AK GUY said:
Any Cities, Counties, or municipalities out there ever request 3rd party testing of Systems resistance to ground if ground conditions might be in question. We have some residences being built in our area where the lot is blasted out of rock, and the foundations are on shot rock. The water services are HDPE, and the footings are insulated and vapor barriered. I have a real concern about developing a grounding electrode system.
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What difference does it make anyway? It is not as if the "quality" of the GES matters all that much.

Do the minimum and be done with it. Especially for a residence.

People worry way more about their GES than is warranted.
 
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