grounding electrode in seawater


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Old 02-11-20, 12:51 PM
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grounding electrode in seawater

I may ask the inspector this question, but will start here.

Subpanel install on a dock over seawater canal. 4 feet of water over silty clay. Can I drop in two stacked ground rods, as to get the 8' actually below seafloor, and bring the top of the top ground rod in the clear, keeping the acorn dry? This would be very near the piling that holds the subpanel. Obviously, now the electrode connection is nice a short, and doesn't have to climb over the seawall to a dirt rod inland.
 
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Old 02-11-20, 04:18 PM
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So the ground rod would be in four feet of salt water to get to solid ground ?
I can't see how that would fly. The salt water will eat up the ground rod(s).

I know you need a ground rod for a sub panel at each building or structure.
I'm not sure if that is the same for a dock panel. I'm looking at the different codes.

There is no clear evidence you need ground rods for your service panel.
I was looking at the NEC 682 but it's not clear either.

Just some info..... Article 555 from Mike Holt (pdf)
 

Last edited by PJmax; 02-11-20 at 05:07 PM.
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Old 02-17-20, 01:16 AM
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Ground rod on a subpanel? Not recommended your creating a ground loop.

Grounding is established at the service/meter location. That is where the neutral/grounded conductor is established. ALL circuits from there must be hot/neutral/ground, assuming 120v.

https://forum.nachi.org/t/private-bo...ectrical/62085

I suggest that you contact your local AHJ (authority having jurisdiction) and have them help you.
 
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Old 02-17-20, 06:10 PM
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A subpanel needs ground rods if it is the first panel in a "different building" and the dock counts as a different building if not connected to the building with the supra panel.

The open question would be about ground rods for pedestal mounted (as opposed to building mounted) subpanels.

I was thinking that a ground rod under the dock in X feet of water would not corrode faster than a ground rod a short distance away, in the beach or bank. The latter rod would be in soil soaked with the same (perhaps salty) water.
 

Last edited by AllanJ; 02-17-20 at 06:35 PM.
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Old 02-18-20, 05:26 AM
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I did call the inspector. He indicated that a ground rod is not required at the boathouse.

However, later I will install a lightning protection system and will revisit a grounding scheme. For that, I am thinking of 1/2” type K or L copper tubing, keeping the wire connection above the waterline. Each end of the structure will get this. I fear that copper clad steel rods will have a short lifetime in the seawater.
 
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Old 02-18-20, 05:30 PM
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I fear that copper clad steel rods will have a short lifetime in the seawater.
I fear the same thing. How about stainless steel ?

I was looking at online 5/8" rod pricing and for a 6' length it was +/- $20.
Couldn't find anything in 8' long.
 
 

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