Additional ground ring around ground-mount array

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msheets

PE Electrical
Location
Salt Lake City, UT, USA
Occupation
Electrical Engineer
I am working with a client on a 2MW ground-mount array. The owner has requested that a "grounding counterpoise" be installed around the perimeter of the array, with each rack bonded to it. The "counterpoise" will basically be a very large ground ring with ground rods. Is this a reasonable request? I have limited experience with this size array, and the other MW+ arrays we have done have not required it. It seems to me like a second grounding electrode system, and about 3,000' of copper. The racks are already going to be bonded to ground with the EGCs run with the positive and negative conductors back to the inverter, where the DC and AC ground bus bars are bonded internally, and there to the system ground.

Thanks in advance.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am working with a client on a 2MW ground-mount array. The owner has requested that a "grounding counterpoise" be installed around the perimeter of the array, with each rack bonded to it. The "counterpoise" will basically be a very large ground ring with ground rods. Is this a reasonable request? I have limited experience with this size array, and the other MW+ arrays we have done have not required it. It seems to me like a second grounding electrode system, and about 3,000' of copper. The racks are already going to be bonded to ground with the EGCs run with the positive and negative conductors back to the inverter, where the DC and AC ground bus bars are bonded internally, and there to the system ground.

Thanks in advance.

I don't think it is either necessary or especially useful. I think that you have an obligation to state that up front.

Having said that, it won't harm anything other than the owner's wallet and it is his money so if he really wants it while fully understanding it serves no useful purpose, it would not bother me one bit if you were to sell him your design expertise to design what he wants.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
I agree with Bob's assessment. However, if they ask I shall provide and charge accordingly. They are the "design" professionals and I am just the labor:angel:
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
If the ground mount method involves the typical steel supports embedded in concrete, all the supports will probably do at least as a job of acting as an electrode as the proposed 'couterpoise'.
 
If the ground mount method involves the typical steel supports embedded in concrete, all the supports will probably do at least as a job of acting as an electrode as the proposed 'couterpoise'.


Thats what I was going to say. I was working on a 1 MW ground mount last month and the structure was steel I beams every 20 feet apart driven into the ground about 15 feet deep. I joked with one of the other guys that we need to add a ground rod at the end of each row ;)
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Actually 690.47(D) allows for the structure to act as an electrode if it meets the right requirements of article 250, which your example would for each of those supports (i.e. steel more than 10' in the ground).

690.47(D) is, IMO, an otherwise horrible and dangerous code section, but at least they got that part right.
 

msheets

PE Electrical
Location
Salt Lake City, UT, USA
Occupation
Electrical Engineer
Thanks for the comments, everyone. I will let the client know that it is an unnecessary addition and see what they want to do. They are notorious for wanting things done as specified, whether it makes sense or not, so I don't have much hope of swaying them, however.
 
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