I'm installing my first system with 2 arrays. I need help understanding the calculations for the back feed breakers.
I have a 200 amp service
I'm installing 2 arrays. I planned to run out from each inverter to their own AC disconnect then to individual meters for the PA Sunshine rebate program and then into the service panel with a backfeed breaker for each array. Forgive me, but I seem to be having brain freeze at the point of interconnection to the service panel. Below are the specs. All assistance is much appreciated.
Solar System Specs:
3 strings of 5 - Sanyo HIP-215NKHA5
The nominal output is 16.7A (According to Section 690.8, the output circuit must be sized at 125% of the rated output) Then the safety factor would make it 20.875A.
There is an Outback combiner box mounted on the roof. EMT runs from the combiner through attic to DC disconnect in garage.
8 AWG wiring from the combiner to the DC disconnect (account for heat running through attic to diminish voltage drop)
EMT runs from the DC Disconnect to the inverter located in the basement. (Utility supplied lockbox for key to basement)
10 AWG wire runs from the DC Disconnect to the Fronius inverter.
3 strings of 6 with the same setup as described above.
From what I understand my backfeed breakers would need to be 25A for each array. When the code refers to OCPDs supplying power would that be the backfeed breaker? So then I would have 50A supplying power.
"The sum of the ratings of the breakers may not exceed 120% of the rating of the bus bar or the ampacity of the conductor." John Wiles
In a 200 amp service is the bus bar rating 200amps? (I believe it is the terminology that throws me not the concepts/theory) If yes then 120% of 200A is 240A. Then my two 25A backfeed breakers are safe to install, right?
My partner spoke to an electrical inspector. The inspector suggested that he has seen installers with two arrays go into a sub panel with one AC disconnect for panel and then only 1 meter. My partner is not trained in solar PV, but he does have a very good knowledge base, but I don't trust that he accurately described the system we are installing. (Since this is my first post I have to figure out how to upload a photo.)
I'm coming to all of you because my electrician seems to be in never never land when I try to discuss this with him about code.
I took my SEI class last year and there is much to remember and understand, let alone try and decipher the NEC 2008 code book.
If I have missed supplying you information please yell and I will get it to the discussion.