Rapid Shutdown for PV Systems

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Understanding NEC 690.12
  • Rapid Shutdown for PV Systems
    Rapid Shutdown for PV Systems
  • Improved control
    To control the PV system circuits leaving this rooftop, firefighters would have to coordinate the operation of 37 rooftop disconnect combiners. If you were to install the same system using contactor...
  • NEC 2014 compliant
    These nine SMA Sunny Tripower inverters, which provide dc arc-fault circuit protection per 690.11, process power from and are installed within 10 feet of a 186 kW roof-mounted PV array. As a result,...
  • Inherently compliant
    PV systems deployed using ac modules or module-level microinverters—like the SMA Sunny Boy 240-US micros shown here—are inherently 690.12 compliant.
  • Rapid-shutdown initiator
    If loss of ac power does not automatically initiate rapid shutdown, system integrators need to install a manual rapid-shutdown initiation switch—such as Bentek’s Rapid Shutdown Controller—to turn off...
  • Rapid-shutdown initiator
    If loss of ac power does not automatically initiate rapid shutdown, system integrators need to install a manual rapid-shutdown initiation switch—such as MidNite Solar’s Birdhouse—to turn off the...
  • Module-level control
    Many dc-to-dc converter systems are well suited to provide rapid-shutdown functionality. For example, SolarEdge power optimizers can control voltage at the module level, and a Nationally Recognized...
  • Capacitor-bank isolation
    If an inverter cannot meet the 30-volt and 10-second limits in 690.12, you need to install a switch to isolate the capacitor bank. In this example, the installer has mounted a contact combiner in an...
  • Normally open contactors
    Contactors are the most common type of remotely actuated switch used in PV systems today. Bentek’s Rapid Shutdown Module (left) places contactors in line with PV source-circuit conductors to provide...
  • Normally open contactors
    Contactors are the most common type of remotely actuated switch used in PV systems today. Larger contactor combiner products—such as the AFCI combiner from SolarBOS—place contactors in line with PV...
  • Normally open contactors
    Contactors are the most common type of remotely actuated switch used in PV systems today. Larger contactor combiner products— such as Solectria Renewable’s ARCCOM —place contactors in line with PV...
  • String inverter rack
    For installations on low-slope roofs, system integrators can use string inverter mounting kits, such as Advanced Energy’s proprietary 3TL horizontal mounting kit, to distribute string inverters...
  • String inverter rack
    For installations on low-slope roofs, system integrators can use string inverter mounting kits, such as SMA America’s custom ReadyRack, to distribute string inverters across an array instead of...
  • String inverter rack
    For installations on low-slope roofs, system integrators can use string inverter mounting kits, such as Bentek’s universal PowerRack with optional sun shade, to distribute string inverters across an...
  • Battery-storage system
    Rapid shutdown is more complex for stand-alone systems or systems with multimode inverters. For example, MidNite Solar’s rapid shutdown system uses a Birdhouse controller to simultaneously open a...
  • Battery-storage system
    Rapid shutdown is more complex for stand-alone systems or systems with multimode inverters. For example, MidNite Solar’s rapid shutdown system uses a Birdhouse controller to simultaneously open a...
  • Rapid Shutdown for PV Systems
  • Improved control
  • NEC 2014 compliant
  • Inherently compliant
  • Rapid-shutdown initiator
  • Rapid-shutdown initiator
  • Module-level control
  • Capacitor-bank isolation
  • Normally open contactors
  • Normally open contactors
  • Normally open contactors
  • String inverter rack
  • String inverter rack
  • String inverter rack
  • Battery-storage system
  • Battery-storage system

The 2014 edition of the National Electrical Code added rapid-shutdown requirements for PV systems on buildings with the goal of allowing first responders to quickly and easily control the PV system circuits leaving a roof-mounted array.

According to market data that the Solar Energy Industries Association (SEIA) and GTM Research published in September 2014, there are more than 500,000 rooftop PV systems installed in the US. Bloomberg estimates that integrators installed roughly 3 GW of rooftop PV capacity on some 200,000 homes and businesses in the last 2 years alone. Due to the proliferation of rooftop solar installations, the regulatory agencies and entities responsible for developing codes and standards have increasingly scrutinized the potential hazards associated with PV systems mounted on buildings, especially with regard to firefighter safety. This scrutiny has resulted in new fire and electrical code requirements pertaining to roof-mounted PV systems. While the solar industry may not welcome the additional regulation, collaborating with the fire service to establish a positive long-term working relationship is critical.

In this article, I attempt to demystify one of the most controversial of these new code requirements—namely, NEC 2014 690.12, “Rapid Shutdown of PV Systems on Buildings.” To explain the historical context that led to these rapid-shutdown requirements, I begin with a brief background on the jurisdictional efforts to enforce fire regulations specific to roof-mounted PV systems. I then explore the technical difficulties associated with protecting firefighters from energized conductors on the dc side of a PV power system, as this establishes the need for rapid-shutdown requirements. Finally, I deconstruct the language in 690.12 and consider its intent and implications. In the process, I provide examples of some equipment configurations that meet these requirements in a variety of real-world applications.

History of Fire Regulations

Fire service concerns about PV systems are not new, but they have increased significantly over the last 6 or 7 years. Los Angeles was the first large jurisdiction in the US to enforce PV system fire regulations. In early 2007, the Los Angeles Fire Department published a set of restrictions for commercial and residential PV systems. These guidelines limited the size of array sections to 50 feet in any dimension and required 4-foot setbacks on all four sides of each array section. Further, the guidelines required “quick-release type” module-mounting hardware, which was subject to fire department approval but otherwise undefined.

Responding to this regulation by a major municipality, in July 2007 the California Solar Energy Industries Association (CALSEIA) began working with the California Department of Forestry and Fire Protection (CAL FIRE) to develop consensus on PV installation guidelines. Together, CALSEIA and CAL FIRE’s Office of the State Fire Marshal put together a task force consisting of fire service and solar industry stakeholders, building code officials, and codes and standards experts. This task force developed installation guidelines for roof-mounted PV systems that CAL FIRE published in April 2008 as recommendations for framing local ordinances (see Resources).

While the CAL FIRE Solar Photovoltaic Installation Guideline does not have the force of law, the 2012 editions of the International Fire Code (IFC) and NFPA 1 Fire Code subsequently codified its major provisions related to array layout restrictions. (See these SolarPro articles for more information: “Commercial Rooftop PV Arrays: Designing for Fire Code Compliance,” August/September 2014; “Pitched Roof Array Layout for Fire Code Compliance,” November/December 2014.) The CAL FIRE Guideline also includes circuit routing and system marking recommendations codified in NEC 2011 690.4(F) and 690.31(E), respectively.

Since the National Fire Protection Association (NFPA) publishes NFPA 70, National Electrical Code, it should come as no surprise that the association emphasizes minimizing the risks and effects of fire and takes a particular interest in firefighter safety. For example, Code Making Panel 4 (CMP4) also added NEC 690.11, “Arc-Fault Circuit Protection (Direct Current),” to Article 690 during the 2011 revision cycle. While arc-fault protection requirements mitigate fire initiation hazards associated with arcing faults, they do nothing to eliminate the shock hazard that PV power circuits present to first responders. Similarly, while the circuit routing and labeling requirements in NEC 2011 help first responders to identify energized PV power circuits, they do not mitigate the associated shock hazards.

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