Interconnected Power Sources (Article 705) and Energy Storage Systems (Article 706)
the 120 Percent Rule, Source Disconnects, Backfed Breakers and ESS Disconnects
NFPA 70 National Electrical Code, 2023 edition · Reviewed 2026-09-21
Lessons 10-01 (PV) and 10-02 (EV) cover the sources and the chargers; this lesson covers how a PV inverter, a battery or a generator connects to the premises wiring in parallel with the utility — Article 705 — and the rules for the energy storage system itself — Article 706. The Class II (unrestricted) exam's renewable-energy items lean on the 705.12 busbar rules and the 705.28/705.30 sizing chain. Written from the 2023 text (the Georgia edition — NEC 2023 with Georgia amendments; 2023 section numbers throughout).
1. The basics — 705.5 to 705.10
- Listing (705.6): interconnection and interactive equipment intended to connect to or operate in parallel with power production sources is listed for the required interactive function, evaluated with a field label, or both (UL 1741: stand-alone sources operate in island mode, interactive in interactive mode, multimode in either).
- Parallel operation (705.5): compatible voltage, wave shape and frequency; synchronous generators need synchronizing equipment. 705.8: installation only by qualified persons.
- Identification (705.10): a permanent plaque, label or directory at each service equipment location (or an approved readily visible location) that (1) gives the location of every power-source disconnecting means for the building (colocated sources may be identified as a group), (2) lists the emergency telephone numbers of off-site entities servicing the sources, and (3) reads "CAUTION: MULTIPLE SOURCES OF POWER".
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