Progress on New Class 4 Circuits

Submitted by Mike Miller, Curriculum and Training Manager

I am sure you have heard about Fault Managed Power and Class 4 Circuits in the 2023 NEC. This is covered  in new  Article 726 of the NEC. This new Class may  redefine how the electrical industry delivers high power safely across long distances—without the traditional risks of shock or fire.

The introduction of Class 4 circuits into the 2023 NEC is the first major power class addition in over four decades. Unlike Class 1, 2, or 3 systems, which rely on fixed power limitations, Class 4 systems use real-time fault monitoring to dynamically manage energy delivery.

At the heart of Class 4 is Fault-Managed Power (FMP)—a system that continuously monitors for faults and instantly cuts power if a hazard is detected. Power is transmitted in controlled pulses from a Class 4 transmitter to a receiver, which converts it to usable voltage for the load. If a fault occurs, the system halts transmission in milliseconds—faster than a blink.

This approach allows Class 4 circuits to safely deliver hundreds or even thousands of watts at voltages up to 450V, far beyond the 100W cap of Class 2 systems, while maintaining a safety profile comparable to low-voltage wiring.

Why It Matters

Class 4 technology is in position to revolutionize sectors like:

• Telecommunications, powering 5G infrastructure over long distances
• Smart buildings, enabling centralized power for lighting, HVAC, and IoT devices
• Data centers, offering efficient, scalable power distribution.

As I prepare for our NEC 2026 Update class, my review of the NFPA’s First and Second Draft Reports for the 2026 Code cycle confirms a significant development: Class 4 Fault-Managed Power Systems will be permitted for use in dwelling units. This marks a notable shift from the 2023 NEC, which restricted such systems to non-dwelling occupancies.

In alignment with this change, the Minnesota Department of Labor and Industry (DOLI)—through its Construction Codes and Licensing Division (CCLD)—addressed the update in the Summer 2025 issue of CCLD Review. The article highlights those recent legislative amendments to:

• Licensing requirements (Minn. Stat. § 326B.33),
• Inspection protocols (Minn. Stat. § 326B.36), and
• Permit fee structures (Minn. Stat. § 326B.37)

All these now support the integration of Class 4 systems under the state’s technology circuit definitions (Minn. Stat. § 326B.31).” These updates provide a regulatory framework to ensure the safe and effective implementation of Class 4 technology.

In my view, Class 4 wiring and Fault-Managed Power Systems have the potential to unlock a wide range of new opportunities for electrical professionals—reshaping how we design, install, and power the world.