### Student:

Could you please explain the reasoning behind your recommendation to put the solar breaker on the opposite side of the main breaker or as far away as possible on the busbar?

### Sean White:

The reason it is better to put the solar on the opposite side of the busbar, which is required when we invoke the 120% rule and a good idea for other applications, is as follows:

If we are feeding more current to the load side of the main breaker, then we are adding to the current from the main breaker. If the solar plus the main breaker exceeds the busbar and the solar breaker is next to the main breaker, then when there are excessive loads in a worst case scenario, we can have too much current flowing to the loads from the spot where the solar and main breakers are feeding the busbar. It would be like having one big breaker if the solar and the main breakers are next to each other.

If we are feeding the busbar from the opposite side of the busbar from the main breaker, then we would have solar currents coming from one side and the utility currents coming from the other way. This way the currents will not be coming from the same place and the solar will actually make it easier on the busbar near the main breaker by relieving the main breaker side of the busbar from excess currents.

In theory, but not in practice, if we had a 100A busbar, a 100A main breaker, 100A of PV on the opposite side of the busbar from the main breaker and then we had 200A of loads, there will be 100A on each end of the busbar and yet 0A in the middle of the busbar. (this would not be to code in the US, however in some countries it is allowed).

In this scenario above, if we had both breakers next to each other, then it would be like having a 200A breaker feeding the busbar and would cause a hot spot on the busbar, which is a fire hazard.