480 volt and 208 volt ground triads

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scrino

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Scenario: A building is served by two outdoor pad mount transformers, one that is 480 volt secondary and one that is 208 volt secondary, and each transformer serves a respective indoor switchboard.

My question is: if each switchboard is to have an outdoor triad ground, is there a minimum distance these ground rings should be spaced apart? Or should they be bonded together? Not the rods in relation to each other but the spacing between each system ground ring.
 
The ground rings should be spaced apart and bonded together. I'm not for sure on the minimum spacing, but at least 6 feet apart seems to come to mind.
 
wirenut1980 said:
The ground rings should be spaced apart and bonded together. I'm not for sure on the minimum spacing, but at least 6 feet apart seems to come to mind.
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If we call them ground 'rings' they must encircle the structure they are protecting. 250.52(A)(4)

I can't answer how far triad grounds should be apart but if two or more serve one building they will be bonded together and are required to be by 250.58
 
Considering that the outermost sphere of influence is like a single rod, I would say the spacing would be the same between the outermost edges of the ring as you would use for two individual rods. A rod length should do it. I saw some specs in a tower grounding app note but I doubt I could put my hands on it right away.
 
scrino said:
Or should they be bonded together?
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I just want to make sure you don't miss the part of mivey's post that points you to 250.58 Common Grounding Electrode. . . . Where separate services, feeders, or
branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used. . . . Two or more grounding electrodes that are bonded together shall be considered as a single grounding electrode system in this sense. :)
 
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