Module-Level Rapid Shutdown for Commercial Applications: Page 3 of 6


SEIA and several prominent member solar companies, both small and large, vigorously oppose module-level disconnection as a sole means of reducing shock hazards for emergency responders. Public comments suggest this opposition is not due to an unwillingness to develop and adopt more-rigorous safety standards, but rather due to questions about the efficacy of the 80 V limit as a means of accomplishing these goals.

“SEIA understands and largely agrees with the fire service’s intent to further enhance rapid-shutdown requirements in the 2017 NEC. SEIA disagrees, however, with the specific requirement limits [as] the incorporation of these limits into the NEC would effectively mandate module-level electronics, resulting in a variety of negative consequences.

“SEIA’s strong contention is that, given the absence of any independent technical justification for the proposed module-level electronics mandate, it is inappropriate for the NFPA to set voltage requirements within the array equipment. Indeed, the NFPA would be setting an arbitrary level of safety based solely on statements from a few existing product manufacturers and not fact-based testing involving a wide selection of performance criteria.

“There are multiple approaches to significantly reduce the risk of shock hazard to firefighters operating within the PV array boundary. In contrast, a module-level electronics mandate would favor certain technologies over others. This is an overly prescriptive approach, which will create a disincentive to develop competing technologies and [will] stifle innovation. It should also be recognized that nearly all module-level electronic devices being sold today are principally designed for power conversion and monitoring—not rapid shutdown.

“The long-term reliability of module-level electronics is also relatively unproven. Indeed, few devices currently being sold for module-level rapid shutdown have undergone long-term reliability testing in the field.

“Reliability is not only a concern for firefighters but also for PV service personnel exposed to the inherent hazards of roof work. The concern here is that unreliable rapid-shutdown devices will significantly, and unnecessarily, increase the amount of time PV installers and electricians spend on rooftops to replace or repair failed devices. And while PV installers and electricians recognize and accept the inherent risks of rooftop environments, no one should have to accept unnecessary exposure to such hazards.”
—John Smirnow, principal, Smirnow Law (representing SEIA)

“The current language requires that only the devices controlling conductors inside the array boundary limit the voltage to 80 V. There is no mention of the conditions under which this device must function; no mention of whether the device needs to periodically self-test; no mention of whether it needs to be fail-safe; no mention of immunity to heat, electrical noise or moisture. To be clear, we don’t think that these requirements should be spelled out in the NEC,  but they are essential to the safe and reliable operation of these devices. Hence, we request that the 80 V requirement be replaced with a new certification requirement. It is critical that this certification requirement be distinct from the other rapid-shutdown requirement, because it will need to provide functionality that is distinct from [that of] the other devices. The rapid-shutdown devices outside the array boundary only need to isolate certain conductors. The devices inside the array boundary need to limit the electrical hazards on the components directly connected to the PV modules, which are always energized. The present language is also silent about the amperage requirement, which is the physical quantity that actually causes harm to humans. With 80 V and no limit on current, it is still possible to electrocute a human.”
—Mark Albers, electrical systems engineer, SunPower

“While SolarCity supports the fire service in its intent to increase safety within the boundary of the array, the first draft of section 690.12(B)(2) has been written in such a way that effectively prescribes a specific type of electronic solution. [MLPE] are complicated devices, with a wide array of functions, but they were never designed for the sole purpose of ‘turning off’ solar modules. Because of their complexity, these devices cannot last as long as solar panels.

“[It] is important to remember that not a single firefighter has been killed while on a building with solar, suggesting that existing safety provisions for PV have been largely effective. Meanwhile, falls remain the number one cause of death among all construction workers. Mandating one device beneath every solar module will directly increase the time solar construction workers will have to spend on the roof to replace them. More time on the roof [equates to] a higher risk of falling.

“Even when [MLPE] devices work as advertised, the [PV] system is never truly shut down. UL confirmed as recently as June, in its evaluation of firefighter [personal protective equipment], that voltages below 80 V still pose a risk. [Reducing the voltage without eliminating] the hazard gives unsuspecting firefighters a false sense of security that only puts them at risk.”
—Duncan Cleminshaw, director of product compliance, SolarCity

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