A New Look At PV Supply Stations

The 2017 National Electrical Code (NEC) will feature the new Article 691, which covers nonutility company, large-scale photovoltaic (PV) electric supply stations with generating capacities of at least 5,000 kilowatts (kW). Facilities covered by this article will have specific design and safety features unique to large-scale PV facilities and will tie into the utility company grid, but will be operated by private concerns.


While many such facilities are already operating successfully throughout the United States, Article 691 will provide technical details on the construction and safety of these large facilities.


Three definitions have been provided. “Electric supply stations” are defined as locations containing the generating stations and substations, including their associated generator, storage battery, transformer and switchgear areas. A “generating station” is defined as a plant wherein electric energy is produced by conversion from some other form of energy, such as chemical, nuclear, solar, wind, mechanical or hydraulic, by means of a suitable apparatus. “Generating capacity” is defined as the sum of parallel-connected, inverter-rated maximum continuous-output power at 40°C in kilowatts.


Section 691.4 requires large-scale PV electric supply stations to be accessible to authorized personnel only and to comply with five requirements. The first requirement is that the electrical circuits and equipment shall be maintained and operated by qualified personnel.


The second requirement is that access to the PV electric supply station shall be restricted by fencing or other adequate means in accordance with 110.31. The second paragraph of 110.31 requires a wall, screen or a fence to enclose an outdoor electrical installation to deter access by persons who are not qualified within the facility. A fence must be constructed at least 7 feet high or a combination of 6 feet or more of fence and at least 1 (or more) foot of three (or more) strands of barbed wire at the top of the fence. In addition, Table 110.31 requires the distance from the fence to any live parts to be a minimum of 10 feet for 601 volts (V) to 13,799V, 15 feet for 13,800 to 230,000V, and 18 feet for more than 230,000V.


The third requirement is that the connection between the PV electric supply station and the system operated by an electric utility for the transfer of electrical energy shall be made by connections to medium- or high-voltage switchgear, substation, switchyard or similar methods so as to safely and effectively interconnect the two systems.


The fourth requirement of the electrical loads within the PV electric supply station shall only be used to power auxiliary equipment for the generation of the PV power.


The fifth requirement is that large-scale PV electric supply stations shall not be installed on buildings.


In addition to these requirements, 691.5 requires all electrical equipment to be approved by listing and labeling, field labeling, or—where products complying with either of the above are not available—by engineering review validating that the electrical equipment is tested to relevant standards or industry practice. Documentation of the construction of the engineered electrical design shall be provided upon request of the authority having jurisdiction (AHJ) based on 691.7. Additional stamped independent engineering reports detailing how the construction conforms to the NEC shall also be provided to the AHJ upon request.


The independent engineer designing the system shall be a licensed professional electrical engineer retained by the system owner or installer. This documentation, where requested, shall be available prior to commercial operation of the station. Section 691.8 requires the direct current (DC) operating voltage calculation be included in the documentation in 691.7.


For PV equipment disconnection, 691.9 permits isolating devices to be more than 6 feet from the equipment where written safety procedures and conditions of maintenance and supervision ensure only qualified people service the equipment. These procedures would be in accordance with 110.1 in the 2015 NFPA 70E standard. Buildings with the sole purpose of housing and protecting supply-station equipment are not required to comply with the rapid shutdown requirements in 690.12.


Since there isn’t a rapid-shutdown system installed on the building, written system shutdown procedures must be available at the station site in the event of an emergency. Where DC arc-fault circuit protection is not provided, 691.10 requires details of fire-mitigation plans to address DC arc faults and must be provided in the documentation required in 691.6. Details of fence grounding and bonding requirements must also be included in the documentation in 691.6.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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