My old house is wired as follows:
- A 100A service to a meter and main panel on the outside of the garage.
- Main panel has a single 100A breaker.
- A 125A rated sub panel inside the garage with house load breakers connected with approximately 30Ft of Aluminum wires.
I am planning on adding a PV breaker in the sub-panel. According to my understanding of the NEC 120% rule for busbars, I should be able to add upto a 125*1.2-100=50A breaker in the sub-panel.
Does the 120% rule still apply normally to this scenario when the 100A main breaker is in another panel? Does the 120% rule also apply to the wires connecting the main panel to the sub-panel?
I haven't checked what gauge those wires are. Do they become part of the bus-bar, so to speak, and could the grid and the PV breaker cause the current on the wire between the panels to exceed 100A?