The sum of the rated current for the solar breaker and main breaker cannot exceed 120% of the bus bar’s rating (National Electrical Code Section 690.64):
Solar breaker + main breaker ≤ 120% bus bar rating
Note: The main breaker rating and the bus bar rating will not always be the same. Sometimes, there could be a smaller main breaker on a larger panel, which would provide more capacity.
For example, what is the maximum solar breaker allowed in a 125 A main service panel with 125 A bus bar?
Solar breaker + 125 A ≤ 1.2 × 125 A
Solar breaker ≤ 150 A - 125 A
Solar breaker ≤ 25 A
When there is not enough room for a solar breaker, there are several options:
- Replace the existing main service panel with a larger panel and main breaker, which can be expensive.
- Bypass the main panel and provide a supply- side connection into the electrical service, between the service panel and the utility meter. This requires coordination with the utility and a licensed electrician to make the connection.
- Downsize the main breaker to make room for the solar breaker. This requires a thorough load analysis of the home’s circuitry to ensure that main breaker will be large enough.
See Code Corner in HP135 for more information on inverter supply-side connections.