Article 712 Direct Current Microgrids.
Code Change Summary: A new article was added to address direct current microgrids.
A DC Microgrid is a power distribution system consisting of more than one interconnected DC power source which then supplies DC-DC converters, DC loads, and/or AC loads powered by DC-AC inverters. Examples of power sources can include DC PV systems, DC wind turbine systems and fuel cells. A DC microgrid is typically not directly connected to an AC primary source of electricity, but some DC microgrids interconnect via one or more DC-AC bidirectional converters or DC-AC inverters.
DC Microgrids are related to the direct utilization of power from DC sources to DC loads such as communications equipment, LED lighting, computer servers, variable-frequency drives, HVAC equipment, and the like. Utilizing the actual direct current, whether generated by wind, PV, fuel cells, or other means, without first converting to AC and then back to DC, results in increased efficiency and potentially smaller and less expensive equipment than AC-coupled methods.
The need for increased efficiency in data centers has driven industries to implement DC microgrids in many data centers worldwide. DC microgrids are a trend that will likely continue and increase around the world.
The new 2017 article provides rules including but not limited to the following:
712.25 Identification of Circuit Conductors.
712.34 DC Source Disconnecting Means.
712.35 Disconnection of Ungrounded Conductors.
712.52 System Grounding including ground fault detection equipment.
712.65 Available DC Short-Circuit Current.
712.70 Overcurrent Protection.
712.72 Interrupting and Short-Circuit Current Ratings.
Part VII. Systems over 1000 Volts.
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:
712.1 Scope. This article applies to direct current microgrids.
712.2 Definitions.
Direct Current Microgrid (DC Microgrid). A direct current microgrid is a power distribution system consisting of more than one interconnected dc power source, supplying dcdc converter(s), dc load(s), and/or ac load(s) powered by dc-ac inverter(s). A dc microgrid is typically not directly connected to an ac primary source of electricity, but some dc microgrids interconnect via one or more dc-ac bidirectional converters or dc–ac inverters.
Grounded Two-Wire DC System. A system that has a solid connection or reference-ground between one of the current carrying conductors and the equipment grounding system.
Grounded Three-Wire DC System. A system with a solid connection or reference-ground between the center point of a bipolar dc power source and the equipment grounding system.
Nominal Voltage. A value assigned to a circuit or system for the purpose of conveniently designating its dc voltage class.
712.4 Listing and Labeling. Any equipment used in the dc circuits of a direct-current micro grid shall be listed and labeled for dc use.