How it works & the NEC rules behind it
When firefighters respond to residential or commercial building fires, high-voltage DC solar circuits (up to 600V or 1,000V DC) present severe shock hazards even when the main electrical utility disconnect is opened. NEC §690.12 requires rapid shutdown systems to de-energize rooftop conductors.
Two Distinct Array Boundaries (NEC §690.12(B)):
- 1. Outside the Array Boundary (§690.12(B)(1)): For conductors located more than 1 foot (305 mm) from the solar array or entering a building interior:
• Voltage must drop to 30 Volts or less within 30 seconds of rapid shutdown initiation. - 2. Inside the Array Boundary (§690.12(B)(2)): For conductors located within the 1-foot array perimeter (between modules):
• Voltage must drop to 80 Volts or less within 30 seconds of rapid shutdown initiation.
• This is universally accomplished using Module-Level Power Electronics (MLPE): microinverters (Enphase, Hoymiles) or DC optimizers/rapid shutdown receivers (SolarEdge, Tigo, APSystems). - 3. Initiation Device (§690.12(C)): The rapid shutdown initiator must be located at a readily accessible location outside the building (often the main service disconnect or a dedicated red rapid shutdown switch).
- 4. Safety Plaque & Labeling (§690.56(C)): A permanent reflective plaque showing array layout and rapid shutdown directory must be mounted at the service equipment.