PV Interconnection 120% Busbar Rule
Load-side PV breaker check against the NEC 705.12 busbar limit (120% opposite-end allowance / 100% otherwise).
Example
You enter
- Main breaker rating (A) 200
- Panel busbar rating (A) 200
- Proposed PV breaker (A) 40
- Interconnection method opposite_end_load_side
You get
- Sum of breakers (A) 240
- Busbar limit (A) 240
- Verdict PASS
Details, formula, and sources
With the supply-side 705.11 alternative.
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).
Free read-only access at nfpa.org/freeaccess.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: main_breaker_a, busbar_rating_a, pv_proposed_a, method, sum_of_breakers_a, limit_a, passes
- Breaker position the 120% allowance requires the PV breaker at the opposite end of the busbar from the mainNEC 2023 705.12(B)(3)(2); the AHJ inspector verifies position at the panel
- Supply-side exemption a 705.11 connection ahead of the service disconnect is governed by service-conductor ampacity, not the busbar ruleNEC 2023 705.11(B)