Codes & Safety Standards

NEC 690.12 Rapid Shutdown 30-Second Voltage Rule

Core Question: What are the legal electrical safety requirements for Rapid Shutdown on rooftop solar installations?

Governing Physics Formula / Design Rule
Inside Array: <= 80V within 30s | Outside Array Boundary (1 ft): <= 30V within 30s

Executive Technical Summary

Rapid Shutdown mandates that when building main power is disconnected, rooftop DC voltage must drop to safe touch levels within 30 seconds to allow firefighters safe roof access.

Detailed First-Principles Explanation

Module-level power electronics (MLPE) like microinverters (Enphase) or DC optimizers (SolarEdge, Tigo) satisfy this requirement natively by shutting off DC string voltage at the individual panel junction.

Critical Field Pitfall & Safety Warning

Traditional string inverters without module-level rapid shutdown receivers cannot legally be installed on residential buildings in the United States and jurisdictions adopting NEC 2017/2020/2023.

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