Back-fed c/b

[mastercarl01]

I understand the 120% busbar rating rule.
Example: 200A service panel with a 150A main c/b.
200A X 1.20 =240A -150A = 90A.
Do I use a 45A back-fed c/b? Because 45A+45A =90A.

 

[Dennis Alwon]

No, IMO that would mean a 90 amp dp breaker.

Is this the article you are using.

705.12(D)2) Bus or Conductor Rating. The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120 percent of the rating of the busbar or conductor.

 

[jaggedben]

The size breaker you use depends on the size of the solar system. The 120% rule defines the maximum you can use. The maximum is definitely a 90A breaker in your case.

In a 204/120 panel, there are two busbars. Each busbar is rated for 200A in your case. Both the main and the solar breaker are double-pole breakers. Therefore each busbar can take one pole at 150A plus one pole at (up to) 90A.

 

[mastercarl01]

Thanks, I understand now. I was reading another post with these figures, and I believe, they were talking about using a double-pole 45A c/b. I know it depends on your system size. I just want to clarify that 45A double pole c/b = 45A and not 90A.

 

[Zee]

yes