Overview

Microgrids, which consist of distributed energy resources like solar PV and wind turbines, provide versatile operation modes to accommodate various system conditions. The three primary modes of operation for microgrids are isolated, islanded, and interactive modes. In previous versions of the NEC, Section 705.50 allowed microgrids to isolate from primary sources and operate in islanded mode. However, it did not specify

or cover the interactive mode of operation for microgrids, leading to confusion regarding the applicability of the

Code for such systems. The 2023 revision of this section clarified this ambiguity by including provisions for

interactive mode operation and detailing the various sources permitted for parallel operation in microgrid systems.

Additionally, it addressed microgrid integration into critical facilities.

Applying the 2023 Code

Microgrids are miniature versions of the larger grid, consisting of distributed energy resources such as solar PV, wind turbines, and battery storage, along with control systems to manage energy flow. Microgrids can operate in various modes depending on the circumstances and requirements. In interactive mode, they are connected to the main grid, allowing for two-way energy exchange, and enabling them to import or export electricity as needed. Isolated mode occurs when a microgrid operates independently from the main grid, relying solely on its resources to meet demand. Additionally, microgrids can function in islanded mode during grid disturbances, isolating themselves to maintain power supply to critical loads and support grid stability.

In previous NEC versions, Section 705.50 allowed microgrid systems to isolate from primary and interconnected power sources and operate in an island mode. However, there was confusion regarding whether this section applied to the interconnected mode of operation. To clarify this, the section was revised in the 2023 version to address the interactive mode of operation and specify the various sources that could operate in parallel within the microgrid system. This change clarifies the permitted modes of operation and the functionality of microgrid systems.

What’s New for the 2023 NEC?

The table below presents a comparison between the 2020 NEC and the 2023 NEC regarding Section 705.50.