250.53 and 250.58 with PV Service Disconnects

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pvgreeze

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Location
Philadelphia
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Electrical Engineer
Hi all, question that I'm sure has been discussed ad nauseam in various forms. With the 2023 NEC more explicitly defining a line side PV disconnect as a "service disconnect," this topic seems relevant.

Here is the scenario: For a roof mounted PV system with a line side PV DS interconnection, we need to establish a grounding electrode system separate from the existing service. NEC 250 has several definitions, requirements, tables, etc. outlining the Grounding Electrode System (GES), the Grounding Electrode Conductor (GEC) and the differences between that and the Equipment Grounding Conductor (EGC).

250.53 outlines the installation requirements for the GES. A basic GES is a ground rod, with installation requirements clearly outlined in 250.53(A). 250.53(A)(2) requires a "supplemental eletrode," with examples given as an additional ground rod, bonding to a grounding electrode conductor, bonding to a grounded service-entrance conductor (the service neutral), etc.

250.58 requires that a common grounding electrode exist "where separate services, feeders, or branch circuits supply a building" and that "Two or more grounding electrodes that are bonded together shall be considered a single [GES] in this sense."

So, with a new service DS, which needs a connection to the existing GES per 250.58, can that existing GES service as the "supplemental electrode" to another ground rod as required by NEC 250.53(A)(2)? Basically, do I need two ground rods and a connection to the existing GES or can I get away with one ground rod and a connection to the existing GES. All connections to the GES are sized per 250.66 and are considered grounding electrode conductors (GECs).

Would love to know people's thoughts. Thanks!
 
pvgreeze said:
Here is the scenario: For a roof mounted PV system with a line side PV DS interconnection, we need to establish a grounding electrode system separate from the existing service
Click to expand...
Why separate? The usual option would be to utilize the existing GES via one of the options in 250.64(D).

Also, what is "DS"?

Cheers, Wayne
 
wwhitney said:
Why separate? The usual option would be to utilize the existing GES via one of the options in 250.64(D).

Also, what is "DS"?

Cheers, Wayne
Click to expand...

DS = Disconnect Switch.

Separate meaning new and distinct from the existing electrical service. One that has a seperately bonded ground & neutral (in the dedicated PV disconnect switch) on a separate service, utilizing the existing GES via a separate GEC to that GES.
 
pvgreeze said:
DS = Disconnect Switch.

Separate meaning new and distinct from the existing electrical service. One that has a seperately bonded ground & neutral (in the dedicated PV disconnect switch) on a separate service, utilizing the existing GES via a separate GEC to that GES.
Click to expand...
Great, so if the existing service on the building has a compliant GES, you don't need to add any additional grounding electrodes. You just need to connect the existing GES to the new service PV disconnect switch grounded conductor via one of the options in 250.64(D). And 250.64(D)(2) permits a separate GEC to the new service PV disconnect if that is your preference.

Cheers, Wayne
 
The file is not really intelligble. I don't see where the DC conductors are run and where the EGC from array to inverters is.

Lightning protection of the type apparently shown in the file is beyond the scope of the NEC. However the NEC requires electrodes for such lightning protection to be bonded to the NEC required GES. I can't speak to the engineering advisability of isolating the LPS from the structure GES, but it's an NEC violation.
 
jaggedben said:
However the NEC requires electrodes for such lightning protection to be bonded to the NEC required GES.
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Certianly true if the lightning protection electrode qualifies as an NEC electrode. If for some reason it doesn't, is there something in Article 250 that would still require bonding it?

Cheers, Wayne
 
There are 3 separate GER for 1) LA isolated frm structure, bare conductor of 6mm copper runs directly from LA to GER, while structure earthing is done sepratly by 6mm copper single conductor insulated which is bonded to same GER of LA. Purpose of doing this is to give lightening curent a direct path.
 
My question is if there are any NEC code violation & do these 3 GER need to be bonded togather at sm point.

GER is 7+ mtr depth, 1/2 inch copper rod 3.2 mtr length bonded with bare coper conductor 6mm which runs to the AC mains. Earth enhancing compound bentonite is used.
 
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