Section 690.11 ?Arc-Fault Circuit Protection (Direct Current)?
Series arc-fault protection requirements for dc PV circuits were first introduced in NEC 2011. However, these requirements applied specifically to PV systems with a maximum system voltage greater than or equal to 80 Vdc, and with dc circuits on or entering a building. In NEC 2014, these requirements are expanded to all PV systems with a maximum system voltage ?80 Vdc, regardless of location. As explained in the ROP: ?PV arc faults in ground-mounted PV arrays can result in grass and brush fires. Such fires can result in deaths and significant property damage, which can be prevented with PV arc-fault protection.? Note that the arc-fault protective device must be listed for use in dc PV systems. The applicable product safety standard is UL 1699B, ?Photovoltaic (PV) DC Arc-Fault Circuit Protection.?
These expanded dc arc-fault protection requirements have immediate and significant implications for PV system designers and installers. When Section 690.11 was originally introduced in 2011, there were no listed devices with which to meet the new dc arc-fault requirements, which slowed adoption and enforcement. For example, Colorado?s Department of Regulatory Agencies began enforcing dc arc-fault circuit protection requirements for PV permits issued only after July 1, 2013, even though the state had formally adopted NEC 2011 2 years earlier, on July 1, 2011. Now that listed PV arc-fault protection means are available, there is no reason to expect a delay in adoption or enforcement of the expanded NEC 2014 requirements.
Where the arc-fault protective device is located is largely a function of PV system size and architecture. Listed string inverters with integral dc arc-fault circuit protection are already available from several manufacturers, including Fronius, Power-One, SMA America and SolarEdge. While central inverter manufacturers are less likely to integrate dc arc-fault circuit protection directly into their products, PV system designers can specify combiner box?level solutions that provide this functionality. For example, SolarBOS offers listed 12- or 16-input arc-fault combiner boxes. If they are appropriately listed, dc-to-dc converters like Tigo Energy?s module maximizer may be able to provide module-level dc arc-fault protection.
PV system designers and integrators should continue to follow the development and availability of listed PV arc-fault protection devices. Over time, the range of listed options will certainly increase, as many manufacturers?including Eaton, E-T-A, Sensata Technologies, Texas Instruments and others?are working to develop cost-effective solutions to meet this growing market demand.
Section 690.12 ?Rapid Shutdown of PV Systems on Buildings?
The rapid shutdown requirements in Section 690.12 are arguably the most important (and contentious) additions to NEC 2014. According to Code expert John Wiles, the senior research engineer at the Southwest Technology Development Institute, ?The rapid shutdown requirements in 690.12 will have significant and far-reaching impacts on PV system designs and the design of PV equipment.?
As originally proposed, for improved electrical and fire safety, Section 690.12 would have required module-level emergency shutdown capabilities for PV systems on buildings. However, the consensus language that was ultimately accepted?developed by members of the CMP No. 4 Firefighter Safety Task Group, the Solar Energy Industries Association (SEIA) Codes and Standards Working Group and the PV Industry Forum?requires that conductors associated with a PV system, whether ac or dc, be able to be de-energized on demand, so that any portion of the conductors that remain energized do not extend more that 10 feet from the PV array or more than 5 feet within a building.
As explained in the NEC 2014 Handbook: ?First responders must contend with elements of a PV system that remain energized after the service disconnect is opened. This rapid-shutdown requirement provides a zone outside of which the potential for shock hazard has been mitigated. Conductors more than 5 feet inside a building or more than 10 feet from an array will be limited to a maximum of 30 V and 240 VA within 10 seconds of shutdown.?
Equipment options. While the equipment used to perform rapid shutdown must be listed and identified, it does not have to be listed specifically for the purpose of rapid shutdown of PV systems. For example, string inverters located on a commercial rooftop within 10 feet of a PV array would meet the requirements of Section 690.12, as would microinverters or ac PV modules installed on the roof of a residence. In both instances, if first responders were to shut down power to the premises, there would be no uncontrolled energized conductors beyond 10 feet of the array.
Listed contactor combiner boxes provide another means of meeting Section 690.12 using off-the-shelf components. Simply locate the contactor combiner boxes within 10 feet of the PV array and find a suitable location for the control switch or button. The contactors will open upon loss of utility power or in the event that the control switch is operated. The voltage and power limits in Section 690.12 still allow for 24-volt control circuits, which can be used to operate contactors in dc combiner boxes and allow for Code compliance in the event that the rapid shutdown is initiated by means other than opening the service disconnect. Another design option is to specify dc-to-dc converters that comply with the rapid shutdown requirements for PV systems on buildings.
