NEC Rapid Shutdown
A National Electrical Code requirement that solar systems be able to quickly de-energize DC wiring on the roof to protect first responders from high-voltage hazards.
National Electrical Code (NEC) Section 690.12 Rapid Shutdown requires that solar PV systems installed on buildings be capable of reducing DC voltage to safe levels within 30 seconds of activation. The requirement protects firefighters, who could be exposed to high-voltage DC (up to 600V) on a roof from energized panels even when the utility grid is shut off — DC electricity cannot be switched off by de-energizing the grid.
NEC 2017 and 2020 require "module-level rapid shutdown" — each panel must be de-energized individually within the array boundary. This effectively requires power optimizers or microinverters on all new installations in jurisdictions that have adopted NEC 2017+. Traditional string inverters without optimizers only meet the older "array boundary" requirement (2014 NEC), which some jurisdictions still allow.
Rapid shutdown requirements vary by local AHJ (Authority Having Jurisdiction) — some states have adopted NEC 2020, others remain on 2017 or earlier. Installers must confirm which NEC edition the local jurisdiction has adopted before specifying system architecture.
Real-World Example
The permit application was rejected because the homeowner's neighbor had recommended a budget string inverter without optimizers — the city had adopted NEC 2020, requiring module-level rapid shutdown, so the installer had to redesign the system with SolarEdge optimizers at an additional $2,400.