Rapid Shutdown for PV Systems: Page 5 of 7
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What labeling must you apply? NEC 690.56(C) specifies the identification requirements for facilities with rapid shutdown. A permanent plaque or directory must include the following wording and capitalization:
PHOTOVOLTAIC SYSTEM EQUIPPED
WITH RAPID SHUTDOWN
The plaque or directory must be reflective, with white letters at least 3/8 inch in height against a red background. Ideally, you should locate the rapid-shutdown labeling where it is most beneficial to firefighters, and it should include simple instructions about how to perform the shutdown.
What are the product listing requirements? Per NEC 690.12(5), rapid-shutdown equipment must be “listed and identified.” This language allows for the use of off-the-shelf products listed for PV applications, including inverters, microinverters, ac modules, dc-to-dc converters, contactor combiner boxes, rapid-shutdown systems and so forth. It also permits other off-the-shelf electrical products—such as contactors, motorized switches and shunt-trip breakers—as long as you use these in accordance with their listings and the manufacturer’s instructions.
Some solar industry stakeholders have argued that AHJs should not enforce rapid-shutdown requirements, basing their argument on language in Article 90: “This Code may require new products…that may not yet be available at the time the Code is adopted. In such event, the authority having jurisdiction may permit the use of the products, constructions or materials that comply with the most recent previous edition of this Code adopted by the jurisdiction.” This is an incorrect application of 90.4. NEC 690.12(5) does not require the use of products listed and identified specifically for rapid shutdown—in which case 90.4 would apply—or even listed and identified specifically for PV systems. You can deploy many listed products in ways clearly “suitable for the specific purpose, function, use, environment, application”—per the definition of “identified” in Article 100—to enable rapid shutdown.
What about the rapid-shutdown initiator? NEC 690.12 does not specify where you should locate the initiating device or what type of device you must install. This lack of detail is intended to provide system integrators and AHJs with the flexibility to adapt rapid-shutdown solutions to the complexities of the built environment. While the best location for a rapid-shutdown device and the required label is typically at or near the service equipment, the fire service may have preplanned emergency response tactics for some large commercial or industrial buildings that favor a different location.
One of the simplest ways to initiate rapid shutdown is to set it up to occur automatically upon loss of ac power. This is why NEC 2014 does not require a specific type of rapid-shutdown initiation device. If you install a roof-mounted residential microinverter system or a commercial PV system using roof-mounted string inverters located within 10 feet of the array, you do not need any special equipment to initiate rapid shutdown; you can accomplish this function simply by interrupting utility-supplied power to the inverters. Some companies have developed various rapid-shutdown switches, and claim that rapid shutdown requires these extra switches. However, you have to install an extra rapid-shutdown switch only when you need to turn the array off by some means other than loss of utility power, as with battery-backup systems or inverters equipped with a daytime backup-power outlet.
NEC 690.12 does not specify how many buttons, switches or movements of the hand are allowed to complete rapid shutdown. Ideally, the process should only require one action. As written today, however, the language in 690.12 provides system integrators and AHJs with the flexibility to consider alternatives. Note that if the system design requires more than one action to initiate rapid shutdown, the 10-second time limit still applies. Therefore, where systems are deployed with more than one initiation device or switch, they should all be in close proximity so that emergency personnel can de-energize all of the PV system circuits on the building within 10 seconds. Further, labeling must clearly identify all of the initiation devices and all of the steps required to complete rapid shutdown.
Compliance in Real-World Scenarios
There are many ways to meet the intent of NEC 690.12 and improve firefighter safety in emergency response situations. I intend the following examples not as an exhaustive list of all possible 690.12-compliant solutions, but rather as a representative list of how to use existing PV products for rapid shutdown. I have organized these examples according to application: residential, commercial and battery backup. However, these are general rather than absolute distinctions. While solutions involving module-level power electronics are more likely to appear in residential applications in the short term, there is no reason you could not deploy them in commercial applications as well—or even in an ac-coupled battery-backup application.