Grounding in Water

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sculler

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I am involved with a mutiple building site built on granite rock where the grounding electrode is a 4/0 CU wire run 40 feet into a diluted salt water bay. Wondering best way to measure grounding resistance?
Facility is fed from private 500KW 12500V hydro system with a 1 M diesel gen set back up feeding into a 600 V distribution system. I am concerned about grounding/bonding I see and would like to start with knowing effectiveness of "water" grd.
 
My first take is that the ground electrode to remote earth resistance is not particularly important for NEC or other practical electrical safety purposes. Only, perhaps for lightning protection, which the NEC does not really address.
That said, all normal techniques for measuring electrode to "earth" resistance require some other reference electrode.
You could probably use several boats and do a three point fall of potential measurement through the water if you are forced to come up with a number.

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The Fluke 1630 Earth Ground Clamp Meter or a similar product measures grounding resistance without the need for reference stakes. Just clamp it around the ground rod or GEC and test. However it's not cheap.
 
jimdavis said:
The Fluke 1630 Earth Ground Clamp Meter or a similar product measures grounding resistance without the need for reference stakes. Just clamp it around the ground rod or GEC and test. However it's not cheap.
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It does not require spaced test electrodes, but it still requires some sort of additional earth connection to use as a voltage reference and as a path for the current injected by the clamp on current transformer.
In most places in the US the POCO MGN will meet that requirement even if you do not have multiple other grounds besides the one you are testing.

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