Rapid Shutdown for PV Systems: Page 3 of 7
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In fact, while stakeholders were revising content from the CAL FIRE Guideline for inclusion in the 2012 IFC, a consultant for the fire service developed language requiring dc disconnects as a means of de-energizing PV power circuits. This proposal was withdrawn only after the Solar America Board for Codes and Standards (Solar ABCs) sent the consultant an 11th-hour communication—subsequently published as Appendix A to the report “Understanding the CAL FIRE Solar Photovoltaic Installation Guideline” (see Resources)—pointing out that PV power systems could shock or electrocute first responders if firefighters did not properly coordinate the operation of these disconnects. Clearly, a more comprehensive shutdown system is necessary to truly address firefighter safety.
Need for rapid shutdown. Fire service representatives are justifiably concerned about the inherent shock hazard that most PV power systems present first responders. Therefore, the NFPA established a Firefighter Safety Task Group within CMP4 to specifically address this issue for NEC 2014. This task group’s primary contribution to the National Electrical Code Committee Report on Proposals was Proposal 4-253, which recommended the creation of a new code section, 690.12, that would apply to roof-mounted systems and address the de-energization of PV power circuits.
The task group originally proposed that NEC 690.12 require module-level shutdown for roof-mounted PV systems. This would have left only the module wiring and the internal conductors energized in the event of a utility outage or manual PV array shutdown. While this language provided first responders with a way to quickly and easily control PV power circuits on a building in the event of an emergency, solar industry representatives objected to the requirements, arguing that module-level technologies were not mature enough for widespread adoption.
Three stakeholder groups subsequently worked together to rewrite NEC 690.12. This process included the PV Industry Forum, SEIA’s Codes and Standards Working Group, and the CMP4 Firefighter Safety Task Group. The resulting proposal is the language published in NEC 2014:
690.12 Rapid Shutdown of PV Systems on Buildings
PV system circuits installed on or in buildings shall include a rapid shutdown function that controls specific conductors in accordance with 690.12(1) through (5) as follows.
(1) Requirements for controlled conductors shall apply only to PV system conductors of more than 1.5 m (5 ft) in length inside a building, or more than 3 m (10 ft) from a PV array.
(2) Controlled conductors shall be limited to not more than 30 volts and 240 volt-amperes within 10 seconds of rapid-shutdown initiation.
(3) Voltage and power shall be measured between any two conductors and between any conductor and ground.
(4) The rapid-shutdown initiation methods shall be labeled in accordance with 690.56(B).
(5) Equipment that performs the rapid shutdown shall be listed and identified.
Note that this language originally appears in Proposal 4-110 of The National Electrical Code Committee Report on Comments (ROC) along with a lengthy substantiation. The substantiating comments are well worth a read if you are looking for a point-by-point breakdown of the deliberations and research that led to the published rapid-shutdown requirements. As with any new Code requirement, understanding the intent of the language in NEC 690.12 will not only help system integrators deploy compliant solutions, but also assist enforcement entities with permitting and inspection.
Understanding Rapid Shutdown
The primary objective of NEC 690.12 is to provide emergency response personnel with a comprehensive and effective means of controlling PV power circuits installed on or in buildings in a manner that eliminates the false sense of security associated with using rooftop dc disconnects. While the Fire Safety Task Group initially proposed module-level shutdown as a solution, the revised language essentially requires combiner-level shutdown near the array.