Electrical
PV Interconnection Method Selector
Pick your service style and enter a few electrical inputs. See every interconnection method that fits, the real wiring diagram, the NEC code basis for your code cycle, and export a method sheet.
Service style
1 method match your service
Backfeed Breaker
120% rule · NEC 705.12(B)(3)(2)
Backfeed breaker in a meter-main combo (no feedthrough panel) using the 120% rule.
Code basis
Backfeed-breaker connection on a meter-main combo busbar (no feedthrough panel). Governed by the 120% allowance against the combo bus: main OCPD + PV breaker ≤ 1.20 × busbar.
- 705.12(B)(2) — 120% busbar allowance (Article 705 reorganized in 2023)
- 705.12(B)(2)(2)(c) — opposite-end placement + label (renumbered)
- 690.8, 408.36, 250.122 — unchanged in concept
About this calculator
The same interconnection logic our platform uses, free to use.
Choosing how a PV system connects to the service is one of the first decisions on every planset, and the one most likely to bounce in plan check when it is wrong. This tool runs the exact method-matching logic from the Solar Design Lab platform: it looks at your service style, busbar and main breaker ratings, and inverter output, then shows the interconnection methods that actually apply, from a load-side 120% backfeed to a supply-side tap to a feed-through tap.
Each method comes with the real wiring diagram and its NEC code basis. The 2020 and 2023 citations are both included because Article 705 was reorganized in 2023, so the section number a reviewer expects depends on the code cycle your jurisdiction has adopted. The PV backfeed breaker is sized automatically to 125% of your total continuous inverter output per NEC 690.8.
Educational reference, not project-specific engineering. Confirm the adopted code cycle, the AHJ's requirements, and the panel's listed busbar rating for every project.
NEC references
- 705.12: Load-side (busbar) interconnection, 120% rule, sum rule, feed-through tap
- 705.11: Supply-side (line-side) connection ahead of the service disconnect
- 690.8(A)/(B): PV breaker sized to 125% of continuous inverter output current
- 408.36: Panelboard overcurrent protection. 250.122: equipment grounding conductor
- Edition-aware: citations shown for both NEC 2020 and NEC 2023 (Article 705 was reorganized in 2023)
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