The DC Task Group of the NEC Correlating Committee is proposing three new articles for the 2017 edition of the National Electrical Code (NEC). The first is Article 706, covering energy-storage systems (ESS). The second is Article 710, covering microgrids. The third is Article 712, covering direct current (DC) microgrids. John Kovacik, Underwriters Laboratories Inc., chaired and was a principal member the DC Task Group. David Conover, senior technical adviser for the Energy and Environmental Division of the Pacific Northwest National Laboratory, chaired the sub-task group for Article 706. Robert Wills, Intergrid LLC, chaired the sub-task groups for Article 710 and Article 712.


These new articles were formulated as public inputs (the new NFPA method of submitting proposals for the 2017 NEC) with a large amount of substantiation. 


Article 706


Article 706 states that “batteries are addressed in numerous locations throughout the NEC, primarily in Article 480 for batteries and Article 690 for photovoltaic installations. The current state of energy storage technology—­which includes lead acid and other types of batteries, with the anticipated evolution of energy storage devices of all kinds—supports the need for a singular set of requirements in the NEC covering all such systems. If this is not accomplished in the 2017 NEC and available to serve as a singular foundation for needed changes in the future, the provisions covering such systems will continue to reside in different places within the NEC, and likely evolve to attach themselves as parts to existing criteria throughout the NEC.”


Batteries are only one type of ESS in Article 706. An ESS is defined as “a device or more than one device assembled together capable of storing energy for use at a future time. ESS(s) include, but are not limited to, electrochemical storage devices (batteries), flowing electrolyte batteries, capacitors, and kinetic energy devices (flywheels and compressed air). These systems can have [alternating current (AC) or or DC] output for utilization and can include inverters and converters to change stored energy into electrical energy.” 


Newly proposed Section 706.4 states that an ESS shall be classified as a self-contained ESS, pre-engineered matched components intended for field assembly as a system, or some other ESS type.


Based on Section 706.5, the equipment involved in the ESS must be listed for the intended application as a complete system. Where these systems are designed and installed to be operated in parallel with a primary source of electricity, the requirements in the following sections will also apply: Section 705.14 (requiring output characteristics of the ESS to be compatible with the characteristics of the electrical supply system), Section 705.16 (requiring the fault current contributions from all interconnected sources to be considered), Section 705.32 (requiring the output of an interactive system to be on the supply side of ground-fault protection where ground-fault protection is used), and Section 705.143 (requiring a synchronous generator in a parallel system to maintain a synchronous condition). Article 706 has five parts, with Part I covering general requirements, Part II covering circuit requirements, Part III covering electrochemical ESS, Part IV covering flowing-electrolyte ESS, and Part V covering kinetic ESS.


Article 710


The proposed Article 710 covers microgrids. A microgrid is “a group of interconnected electric loads and power production sources that comprise an electric power system with a clearly defined electrical boundary. A microgrid may include portions of an electric power system that are normally operated by a utility. Microgrids are also known as minigrids.” 


An interactive microgrid is capable of operating in parallel with a primary power source, an islanded microgrid is an interactive microgrid operating in island mode, and a standalone system is a microgrid that operates independently from a primary power source. An islanded microgrid transitions to island mode and is typically an intentional response to utility demand requirements or disruption of the primary power source. Standalone systems are also known as isolated microgrids, islands or prime power systems.


Article 712


In Article 712, a DC microgrid is defined as a power distribution system consisting of one or more interconnected DC power sources, DC-DC converters, DC loads, and AC loads powered by DC-AC inverters. A DC microgrid is typically not directly connected to a primary source of electricity, but some DC microgrids interconnect using one or more AC-DC converters or bidirectional inverters. 


Follow the 2017 NEC process to learn the results and progress of these new proposed new articles.