Solar Backfeed Breaker Size

We sometimes see people adding a 60 or 80 a breaker instead.

Solar backfeed breaker size.

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. If a 200 a busbar has a 200 a main breaker the code allows adding a up to a 40 a backfeed breaker. I am not a code expert or electrician.

Now these are often included with some inverters but it s a good idea to check. 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. 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. 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.

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