(Imax X 1.25) + main supply OCPD <= Busbar rating
How big of an inverter can I connect? Rearrange the formula:
Imax <= (busbar rating – main supply OCPD) / 1.25
Example:
225 A busbar, 200 A main supply OCPD
Imax <= (225 A – 200 A ) / 1.25 = 20 A = 20
Imax <= 20 A
Therefore you can install UP TO a 20 A total inverter imax
705.12(B) Busbar ratings – SIX OPTIONS
| 1. “100% rule” | 125% of power source output current + primary source OCPD protecting busbar <= Ampacity of busbar |
| 2. “120% rule” | Two sources at opposite ends of busbar: 125% of power source output current + primary source output current + Primary source OCPD protecting busbar < = 120% of busbar ampacity |
| 3. “Inverter AC combiner panel” | Sum of ampere ratings of all load and power source OCPDs in panelboard <= Ampacity of busbar |
| 4. “Center-fed panel in dwelling” | This is same as option 2 above |
| 5. Engineering supervision for multiple-ampacity busbars | |
| 6. Busbars in panelboards that supply lugs connected to feed-through conductors |