Solar Backfeed Breaker Size

Select the breaker size that can carry the current with common breaker sizes being 30 amps 40 amps or 50 amps.

Solar backfeed breaker size.

The nec allows adding a back feed breaker so that the current supply is up to 120 of the rating of the bus bar. Having said that a 200a rated panel with a 200a main breaker would allow up to 40a of backfeed breakers placed at the opposite end of the panel busbars from the main breaker. Use the ampacity tables to select the cable corresponding to the breaker size with a 30 amp breaker requiring a 10 3 cable a 40 amp breaker an 8 3 cable and a 50 amp breaker a 6 3 cable. We sometimes see people adding a 60 or 80 a breaker instead.

To calculate the fuse size required between the string and the inverter s dc input you take 9 12 x 1 56 14 7 and round up to the next trade size of 15a. Understand that corresponds to 32a of pv current maximum. However if we add our pv breakers into a sub panel that is dedicated to only the pv breakers we can land the sub panel into a 40a breaker in the main panel board 10 4a 21a 31 4a x 1 25 39 25a. If a 200 a busbar has a 200 a main breaker the code allows adding a up to a 40 a backfeed breaker.

The sizing of back feed breakers is another point of difficulty. Then looking at that photo again you can see i have a 30a 2 pole breaker at the other end for my solar inverter.