NEC 2017 207.12 (B)(2)(3)(a)

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thamessolar

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Denver, Co
Can you give me your opinion of which of the following methods you agree with? Our state inspector uses you as a reference for requiring method two.
Question: Is the 100 amp busbar in the garage panel adequate or does the code require it to be increased to 200 amps?


Method one – My understanding using NEC 2017 705.12(B)(2)(3)(a) – 125% of the inverter output current rating plus the utility fed main breaker does not exceed the busbar rating.
20.96A x 1.25 = 26.20A +50A main = 76.2A < 100 busbar.
Therefore, the existing 100a garage panel is adequate.

Method two – Colorado State Electrical inspectors understanding of the NEC. The code requires that the size of the breaker being backfed by a PV inverter onto a panel busbar does not exceed 20% of the busbar rating
200A busbar x 20% = 40A backfed breaker
Therefore, the panel busbar must be increased to 200 amps.
 
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