Module-Level Rapid Shutdown for Commercial Applications: Page 2 of 6
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Which Side Are You On?
In the first draft of NEC 2017 690.12(B)(2), fire service representatives established a voltage limit of 80 Vdc within the array boundary, effectively mandating MLPE for all building-mounted PV modules. SEIA and other PV industry leaders pushed back during the public comment stage, even going so far as to commission the independent engineering firm DNV GL to study firefighter rooftop operations and hazards encountered while working around PV arrays, and to compare mitigation methods (see Resources).
Unless you actively track the Code development process, you may have missed out on the industry-wide gnashing of teeth regarding the module-level rapid-shutdown language in NEC 2017. The public comments associated with the first draft of section 690.12, “Rapid Shutdown for PV Systems on Buildings,” make for interesting reading because they illustrate the lines of debate and clarify the major concerns on both sides. Excerpts from this debate, edited for length and clarity, follow.
ALL IN FAVOR, SAY AYE
Firefighters are the most vocal advocates of the 80 V limit within the array, undoubtedly because module-level rapid shutdown sounds like it might render an array touch-safe. Not surprisingly, several vendors with module-level rapid-shutdown solutions also support the 80 V limit.
“Representing firefighters, I support the effort to shut down PV systems to the module level during emergencies. The recent proliferation of solar systems in our jurisdiction is having an impact on firefighters’ ability to respond to fire emergencies. Access and egress during rooftop operations and the inability to control utilities for the entire structure are concerns. It is vital that the Code development process recognize the need to protect firefighter safety. This proposal utilizes existing technology to do just that.”
—Richard Doane, fire marshal, Chico Fire-Rescue
“[PV system] circuits remain energized anytime the modules are illuminated and up to the maximum system voltage of 1,000 Vdc. This results in increased danger to first responders when the structure has been damaged. Historically, this has been accepted since there was no practical way to isolate a PV module from the PV source circuit that would operate remotely and on all PV modules in an array simultaneously. Module-level products were not readily available to provide this functionality. Today, this is no longer true: Many reliable products are available that can be either incorporated into a PV module or added to a PV module in the field to provide PV module isolation by remote control. The reliability concerns from 2014 are no longer relevant today, and market data estimates that up to 10 million units capable of module-level isolation are now in service.”
—James Penn, fire inspector, Compton Fire Department
“[The] Fire Marshal’s Association of Colorado supports the language in the first revision as well as the work from the Firefighter Safety and PV System Task Group. PV systems on rooftops can present several hazards to firefighters, the most serious being electric shock in an emergency situation. This section and the proposed change is a significant step forward in improving firefighter safety.”
—David Lowrey, fire marshal, Boulder Fire-Rescue
“[No] other appliance [is] allowed to be used in and around populated areas where there is not a clearly designated switch, plug or other de-energizing method for fully deactivating the system. Why should solar be any different? This industry inconsistency results in an even greater hazard to those untrained in solar, as the default expectation is that all electrical systems can be turned off and are fundamentally safe.”
—Tim Johnson, vice president of customer quality, Ten K Solar
“Enphase Energy supports the language proposed by Code Making Panel-4 [CMP-4], especially the reduced voltage level within an array when initiated by emergency personnel. Rooftop PV arrays should be able to [be] shut down to safe voltage levels in the event of emergency conditions. This is particularly important when considering the life span of a system, as older systems may present electrical hazards to emergency personnel.”
—Mark Baldassari, director of codes and standards, Enphase Energy