705 Part IV. Microgrid Systems.
Code Change Summary: Part IV was added in Article 705 to address interconnected microgrid systems.
A Microgrid System is defined in 705.2 as a premises wiring system that has generation, energy storage, and load(s), or any combination thereof, that includes the ability to disconnect from and parallel with the primary source. These systems have also been referred to as “intentionally islanded systems”.
Microgrids are small energy systems consisting of energy sources, storage, and loads that can operate in parallel with, or independently from, the main utility power grid. Many think of microgrids on the larger side of the smaller scale such as those microgrids used to provide local, reliable, and affordable energy to homes and businesses nearby the microgrid installation. The new definition of a microgrid mentions that a microgrid is part of a “premises wiring system”. Since the applicable size of the microgrid has not been specified in the new code language, some may argue that any interactive PV system using a muitimode inverter and equipped with battery storage is considered a microgrid.
In the 2017 NEC®, the new rules on interconnected microgrid systems are short and take up only a small portion of a single page. It is expected that this new part of the article will see many revisions and expansions in future code cycles.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2017 Code Language:
N Part IV. Microgrid Systems
705.150 System Operation. Microgrid systems shall be permitted to disconnect from the primary source of power or other interconnected electric power production sources and operate as a separate microgrid system.
705.160 Primary Power Source Connection. Connections to primary power sources that are external to the microgrid system shall comply with the requirements of 705.12.
705.165 Reconnection to Primary Power Source. Microgrid systems that reconnect to primary power sources shall be provided with the necessary equipment to establish a synchronous transition.
705.170 Microgrid Interconnect Devices (MID). Microgrid interconnect devices shall comply with the following:
(1) Be required for any connection between a microgrid system and a primary power source
(2) Be listed or field labeled for the application
(3) Have sufficient number of overcurrent devices located to provide overcurrent protection from all sources