I have a theoretical question:

I am an electrician, and was performing some work on a customer's house, when I noticed a 70A PV backfeed breaker inside the Cooper B-line 300A Meter-main load center combo. I asked the homeowner about the PV system, and he informed me that he has a 60 module PV system comprised of Enphase M215 microinverters. The spec sheet for the M215 shows a nominal output current of 0.9A, thus making the total output current (0.9A)(60)=54.0A. Sizing the breaker to 125% gives (54A)(1.25)=67.5A, which explains the 70A breaker, but exceeds the allowable feedback of the 300A enclosure by a theoretical 7.5A if considering the actual output current of the microinverters, or 10A if considering the OCP size. The main enclosure is a 300 amp rated enclosure with a 300 amp main breaker, so my understanding is that the maximum allowable feedback breaker would be 60A, with an actual maximum output current on the microinverters of 48.0 amps - to comply with the breaker being 125% of the continuous load. The PV breaker is also located at the opposite end of the buss as the main breaker. To me, Kirchoff's law seems to say that the sum of the current flow through any point of the buss bar cannot possibly exceed the rating of any load breaker, which are all either 2P100 or 2P50 breakers. Am I missing something? Do I need to tell the homeowner that he is at risk of having an electrical meltdown in the enclosure, or does Kirchoff's Law of Current Flow show that, theoretically the system is fine, just violates the 120% rule? I don't want to open my mouth to the homeowner without making sure I know what I'm talking about. Any insight would be appreciated.

I am an electrician, and was performing some work on a customer's house, when I noticed a 70A PV backfeed breaker inside the Cooper B-line 300A Meter-main load center combo. I asked the homeowner about the PV system, and he informed me that he has a 60 module PV system comprised of Enphase M215 microinverters. The spec sheet for the M215 shows a nominal output current of 0.9A, thus making the total output current (0.9A)(60)=54.0A. Sizing the breaker to 125% gives (54A)(1.25)=67.5A, which explains the 70A breaker, but exceeds the allowable feedback of the 300A enclosure by a theoretical 7.5A if considering the actual output current of the microinverters, or 10A if considering the OCP size. The main enclosure is a 300 amp rated enclosure with a 300 amp main breaker, so my understanding is that the maximum allowable feedback breaker would be 60A, with an actual maximum output current on the microinverters of 48.0 amps - to comply with the breaker being 125% of the continuous load. The PV breaker is also located at the opposite end of the buss as the main breaker. To me, Kirchoff's law seems to say that the sum of the current flow through any point of the buss bar cannot possibly exceed the rating of any load breaker, which are all either 2P100 or 2P50 breakers. Am I missing something? Do I need to tell the homeowner that he is at risk of having an electrical meltdown in the enclosure, or does Kirchoff's Law of Current Flow show that, theoretically the system is fine, just violates the 120% rule? I don't want to open my mouth to the homeowner without making sure I know what I'm talking about. Any insight would be appreciated.

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