PHOTOVOLTAIC SYSTEMS ON BUILDING ROOFTOPS have increased exponentially over the last decade. Better technology, tax breaks at all levels of government, and financial incentives offered by utilities have all contributed to owners pushing the “this makes sense” button and installing photovoltaic (PV) systems at or on their buildings.
But the PV revolution has a downside, too. While the installation rules for these systems have always focused on the core fire and shock protection mission of the National Electrical Code®, the unique nature of a system that cannot be turned off (unlike calling the local utility and asking for power to a building to be “cut”) and the risk it presents to first responders has created the need to improve the safety of these systems when emergency response is involved. While access and marking features such as those found in Chapter 11 of NFPA 1, Fire Code, can improve the safety of first responders, other measures are available to further enhance safety.
The NEC has included safety requirements for PV systems since the 1984 edition, and the 2011 NEC addressed the issue with the inclusion of more robust requirements covering the identification, location, and type of wiring method for PV conductors installed on and in buildings. Additionally, new requirements on direct current arc-fault protection sought to mitigate the PV system against becoming an ignition source. These requirements were certainly safety upgrades, but the head of the monster was still alive. How could the entire PV system be disabled so that firefighters eliminated the risk of a rooftop full of energized equipment and conductors?
The 2014 NEC contains a new requirement that provides a solution to this problem: “rapid shutdown,” a device that can quickly reduce the power output of a PV system. For firefighters, this means that a pre-incident plan for a building can now include the location of the rapid-shutdown device, and when this feature is activated, the power drops to a level that does not present shock or burn hazards to responders if they inadvertently come into contact with PV equipment while conducting firefighting operations on the building’s roof.
Within 10 seconds of activation, the rapid-shutdown system reduces the voltage level to not more than 30 volts, and the overall power in the system to not greater than 240 volt-amperes, levels that mitigate shock and electrical burn hazards. This reduction in energy must occur in PV system conductors that are more than 10 feet (3 meters) from the array or to interior PV system conductors that are located more than 5 feet (1.5 meters) from where they enter a building, since a “hot zone” can still exist near the PV modules.
Some jurisdictions have adopted the 2014 NEC, but have delayed implementation of this requirement pending the availability of a complete certified, or listed, package that allows the rapid shutdown. Other jurisdictions have chosen to immediately implement this requirement and use products such as utility-interactive string inverters and micro inverters to achieve the intended result.
Solar electric power is a terrific technology that is fulfilling the ever-increasing demand for affordable, reliable, and sustainable sources of electric power. The unique hazards that rooftop systems can present to the fire service are being addressed through thoughtful and pragmatic approaches in the NEC. This process will continue to evolve in subsequent revisions of the NEC so that everyone, including firefighters, can look to rooftops and be assured that there is a sustainable and safe source of electrical power.