Section 705.12/Point of Connection for Interconnected Power Sources
NEC 705.12 covers supply-side and load-side connections for solar PV and battery storage including the 120% bus rule.
Interconnected power production sources (solar PV, battery storage, wind, generators) must connect to the premises wiring system using either a load-side connection (Section 705.12(B)) or a supply-side connection (Section 705.12(A)). Load-side connections are made at the service panelboard using dedicated circuit breakers; the sum of overcurrent device ratings on the bus must not exceed 120% of the bus rating (the "120% rule"). Supply-side connections are made between the utility meter and the service disconnect, bypassing the bus ampere limitation. Both methods require a disconnect, proper overcurrent protection, and labeling at the service equipment.
Why this section exists
When a solar inverter or battery system feeds power into a panelboard, the bus and conductors carry both utility current and inverter current. Without the 120% rule, the combined current could exceed the bus rating, causing overheating and fire. The supply-side connection avoids this limitation by connecting upstream of the panelboard bus but introduces different safety considerations (working on energized conductors between the meter and disconnect). Both methods have specific safety requirements to prevent backfeed hazards.
What plan reviewers look for
Plan reviewers check the one-line diagram for the point of connection. For load-side connections, they verify the 120% rule: the sum of the main breaker and the inverter breaker must not exceed 120% of the bus rating. For supply-side connections, they verify the location between the meter and service disconnect. They check for the required disconnect, overcurrent protection, and directory labeling at the service equipment.