Solar Backfeed Breaker Size

If a 200 a busbar has a 200 a main breaker the code allows adding a up to a 40 a backfeed breaker.

Solar backfeed breaker size.

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. Understand that corresponds to 32a of pv current maximum. 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. Then looking at that photo again you can see i have a 30a 2 pole breaker at the other end for my solar inverter.

I am not a code expert or electrician. We sometimes see people adding a 60 or 80 a breaker instead. 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. Nec705 12 b 2 3 b states that where there are two power sources the grid and the solar inverter the sum of their breakers cannot equal more than 120 of the busbar rating of the breaker box.

The nec allows adding a back feed breaker so that the current supply is up to 120 of the rating of the bus bar. Select the breaker size that can carry the current with common breaker sizes being 30 amps 40 amps or 50 amps.