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 converter systems that comply with the rapid shutdown requirements for PV systems on buildings.
Identification and location. The power-source identification requirements for facilities with rapid shutdown are found in Section 690.56(C). A permanent plaque or directory must be provided that includes the following text:
PHOTOVOLTAIC SYSTEM EQUIPPED
WITH RAPID SHUTDOWN
This label must be reflective, with white capitalized letters (3/8 inch or taller) against a red background. These formatting requirements are consistent with those found in the 2012 International Fire Code. Reflective labels are intended to both alert first responders to potential hazards?such as conduits containing PV source or output circuits [see 690.31(G)(4)]?and allow them to quickly identify the means for de-energizing these circuits. Ideally, additional language will specify the appropriate shutdown procedure and a directory will identify the extent of the controlled circuits.
While the Code does not specify where the control point for rapid shutdown equipment is to be located, this is not an oversight. According to Brooks, who submitted the original proposal, the lack of specificity is intended to provide integrators and AHJs with the flexibility to determine the best location for each site. Brook explains: ?Since the goal of rapid shutdown is firefighter safety, the ideal control point for the rapid shutdown system is wherever fire service personnel will go to shut off electricity to the site in the event of an emergency. Most of the time, the electric utility control point is at the service disconnecting means. However, there may be situations where the fire department?s utility control point for a facility is not the location of the service disconnecting means. Rather than requiring a specific location, Section 690.12 allows for flexibility.?
Because PV systems vary considerably in terms of configuration and architecture, this design flexibility is important. For PV systems without energy storage, designers may choose to initiate rapid shutdown whenever utility voltage is lost. In this scenario, PV system circuits on or in a building are controlled whenever a disconnect or circuit breaker in the inverter output circuit is opened, the utility meter is pulled, the main service disconnect is opened, there is a general grid outage and so forth. However, PV systems with energy storage will require a different approach, one that ensures that battery circuits and backup loads shut down only during an emergency and not simply whenever utility voltage is lost.
