In this episode we are talking about 2020 NEC 705.12 (B)(3)(1) and (B)(3)(2). These are some of the most commonly utilized sections that we refer to when interconnecting PV systems to the utility grid.
Can you please give an example of creating a "hot spot" on the bus? We use the 120% rule often at our company but I don't fully grasp how having them at opposite ends protects the bus. The main breaker is assuring you cant exceed 200 on the 200 rated bus and the branch breakers assure the load amperage is evenly distributed on the bus. So if the main and pv breaker were directly on top of each, where would the hot spot occur and why?
Thanks @jessesilver this is a good answer. @Sitesurvey9296, you have to consider all the sources of power. In this example, we have power coming from the utility and the solar. If those two sources were at the same end of the busbar, they could add together and exceed the rating of the bus, creating a “hotspot”. By placing them at the opposite ends, the current flows from the ends towards the middle and there isn’t any place they can be additive. If there is current from both the utility and the solar, the power is sent off to the loads through the branch circuits and there isn’t anywhere on the busbar where the current can exceed the bus bar rating.
