PV Interconnection 120% Busbar Rule
Load-side PV breaker check against the NEC 705.12 busbar limit (120% opposite-end allowance / 100% otherwise), with the supply-side 705.11 alternative.
Formula and source
Load-side: sum = main + PV_existing + PV_proposed; limit = 1.20 * busbar (breaker at the opposite end of the busbar from the main, NEC 705.12(B)(3)(2)) or 1.00 * busbar (other load-side position, 705.12(B)(3)(1)); pass when sum <= limit. Supply-side connection (705.11) is ahead of the service disconnect and is not subject to the busbar rule.
NEC 2023 (NFPA 70). Article 705 (705.11 supply-side; 705.12 load-side busbar).
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