PV System Connected to 480V system with GFCI protection

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Location
New York
Hello all.

I'm looking to connect a 100KW+ PV system to an existing office building which has a 277/480V service and ground fault protection at the existing main since it is over 1000A. The connection will take place on the existing 120/208V distribution which is physically far away from the service.

Can I connect my PV system downstream of the existing GFP device at the main?

My concern is that the GFP device at the existing service main will see the unbalanced current from the system and potentially cause it to trip.

PV SYSTEM.jpg

Thanks all!
 
Location
New York
The 480 to 208Y/120 transformer will prevent any of that issue.

Could you elaborate? I don't see how the transformer prevents the GFP at the main from seeing a different amount of current coming in vs. going out.

Since there is no neutral path back to the inverter from the unbalanced load's neutral on the delta side it seems like it must go back through the GFP at the main.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Codewise...

One issue is that 705.32 prohibits connecting to the load side of GFP, although there is an exception that may allow it if the PV system has its own GFP. I've really never thought about what that means if there's a separately derived system involved.

Another issue is that, transformer or no transformer, the main service GFP device has to be approved for backfeeding, which I'm told is unlikely.

I can't speak from personal experience, but I think that those on this forum who've actually participated in such installs will tell you that a connection on the supply side of the service GFP is your only feasible option.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
Check with the main breaker manufacturer. They will tell you if the GFP Main breaker is suitable for back-feed. I have installed a load-side connected PV system in this situation and was able to confirm that the main breaker at the site was suitable for back-feed, but I was not able to source a GFP back-feed breaker for the 277/480 panelboard we were back-feeding (I was told no one makes them). I solved this problem by installing a GFP device in the inverter output circuit in series with the back-feed breaker. The electrical engineer and the AHJ both approved the installation. The job was at a school, which necessitated a state electrical plan review.
 
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