By Chris Jensen, Regulatory Services Manager; Distinguished Member of Technical Staff – William Henry Merrill Society
Microgrids have emerged as a critical component in the evolving energy landscape. These flexible power systems offer the potential to address pressing issues in our current energy paradigm and enable the use of renewables and energy storage. Microgrids can help operators meet the increasing demand for a reliable and resilient energy supply amidst extreme weather events, natural disasters and grid failures. In remote or rural areas where access to the central grid is challenging, microgrids provide a feasible option for electrification.
Though microgrids are attractive as an alternative to traditional, centralized grid reliance, integrating various power sources may present safety and interoperability challenges.
What is a microgrid?
The National Electrical Code® (NEC) defines a microgrid as follows: “an electric power system containing interconnected power production sources and capable of acting as a primary source independent of an electric utility.” Microgrids can include, but are not limited to, power sources such as photovoltaic systems, engine generators, fuel cell systems, wind turbines, energy storage systems (ESSs) and electric vehicles with power export capabilities. A microgrid can operate as a stand-alone system where it is never connected to a grid or as a grid-connected system with the capability of disconnecting from the grid and operating independently (island mode). Microgrids can operate with alternating current (AC) or direct current (DC).
The NEC contains requirements to address microgrids primarily in Part II of Article 705 for interconnected electric power production sources. These requirements address:
- Connections to primary power sources
- Reconnection to primary source
- Microgrid interconnect devices (MIDs)
- Microgrid control systems (MCSs)
In addition to Part II of Article 705, Article 517 for healthcare facilities, Article 700 for emergency systems and Article 701 for legally required standby systems contain specific requirements for the use of microgrids as part of the standby systems addressed in those Articles. Other articles, including Article 702 for optional standby systems and Article 710 for stand-alone systems, would apply if a microgrid was used as part of these systems, but neither article contains specific requirements for microgrids.
The increasing complexity of microgrids
Even with the current NEC provisions, electrical inspectors may be uncertain whether these requirements are adequate to address microgrids and how to evaluate complex systems. Challenges facing code authorities include:
- Most microgrids are unique and may include a mixture of new and legacy equipment.
- Microgrids can operate in several different modes, and addressing safety and compatibility across all possible modes of operation and grid connection can be difficult.
Several factors contribute to the increasing complexity of microgrid systems, including:
- Prosumer loads — loads that consume and provide power, such as bi-directional electric vehicle power transfer)
- New microgrid topologies — different connection configurations of distributed energy resources (DERs)
- Complex software including safety functionality, such as the distributed energy resource management system (DERMS, the “brains” of the microgrid)
- Utilization of equipment outside its original certified functionality
- Difficulty performing field tests on a specific microgrid
Hazards presented by microgrids
Microgrid systems pose many hazards that must be addressed, such as interoperability and power quality for AC or DC power being produced and distributed.
When microgrids are connected to the electric utility grid, power quality is highly regulated. During island mode, electric utility regulations do not apply, and there is not an enforceable, comprehensive set of requirements to help ensure adequate power quality support. As a result, voltage and frequency may drift outside of safe values for the connected utilization equipment.
Utilization and power distribution equipment are listed (certified) based on the assumption of voltage and frequency supply that does not vary beyond specific limits. Supply voltage and frequency outside of these parameters can introduce safety issues, such as overheating, insulation breakdown and unintended operation.
Since microgrids are made up of multiple DERs that are listed (certified) to operate independently, it is critical that these components also be evaluated as a system for interoperability.
During island mode or in a stand-alone system, unexpected hazardous conditions must be addressed. One example of a hazardous condition is the potential for backfeeding power in unexpected pathways operating in parallel, such as with a battery/inverter source during large load step changes.
Cybersecurity is another potential concern with microgrids. The advent of advanced software and artificial intelligence (AI)-assisted power management has given microgrid operators the opportunity to build more sophisticated control processes. However, the inherent connectivity needed for autonomous management and the Internet of Things (IoT) presents a vector for cyberattacks. As microgrid systems proliferate, so do the risks of infiltration by threat actors.
Mitigating potential hazards with microgrids
To address potential hazards and promote safer deployment of microgrids, UL Solutions initiated work on drafting safety requirements. This led to collaboration with industry, code authorities and others. As a result, UL Standards & Engagement published UL 3001, the Standard for Distributed Energy Resource Systems, on April 24, 2025. Today, it is the national standard for safety for these systems for both the U.S. and Canada. This Standard applies to microgrids comprised of multiple DERs, including those that power corporate campuses, hospitals, universities and communities. UL 3001 provides a means to evaluate the impact on the risk of fire and electric shock created by interactions between the various sources and operation of the DER system as a whole. UL 3001 requires that DER systems be provided with complete instructions for installation, operation and maintenance of the system. The installation instructions include a detailed description of the installation in accordance with the NEC, and the Canadian Electrical Code (CEC) CSA C22.1. The operating instructions for the DER system contain instructions on the testing and maintenance of the DER system if required. Additionally, the operating instructions contain a list of all DER energy sources and critical safety systems and components contained within the DER system.
DER systems that have been evaluated to UL 3001 can provide code authorities with the necessary documentation and certifications that they need to approve the installation in accordance with the NEC and CEC.
To address smaller residential and light commercial microgrids UL Solutions is developing UL 3010, Safety of Single Site-Energy Systems. This Outline of Investigation is being developed for residential and small commercial microgrids found within single-family homes, commercial environments, or other single buildings. These requirements will provide the same level of safety as the larger systems and provide AHJ’s with evidence the system has been evaluated to national standards.