What Is Class 4 Fault-Managed Power?
Class 4 Fault-Managed Power (FMP) is a new electrical circuit classification introduced in the 2023 National Electrical Code (NEC) Article 726. It sits alongside the long-established low-voltage circuit classes defined in NEC Article 725 (Class 1, 2, and 3) but operates on fundamentally different safety and distribution principles. Where traditional classes rely on inherently limited energy or overcurrent protection, Class 4 relies on continuous fault detection at the source to make the system safe to touch even at elevated DC voltages.
The Core Principle: Packet-Based Energy Transmission
A Class 4 system transmits electrical energy in discrete, monitored packets rather than as continuous power. The source — referred to in the NEC as a Class 4 power source — monitors each packet for signatures indicating a fault condition such as a short circuit, ground fault, cable break, or human contact. If a fault is detected, the source shuts off power output within milliseconds, before a harmful energy transfer can occur. This behavior is the basis for the system's touch-safe classification.
This technology is also marketed under several vendor-specific and descriptive names, including Digital Electricity (a trademark of VoltServer), Packet Energy Transfer (PET), and Pulsed Power. NEC Article 726 uses the term Fault-Managed Power as the normative designation regardless of vendor implementation.
What NEC Article 726 Actually Changes
A New Circuit Class with Its Own Article
Prior to the 2023 NEC, no code framework existed for fault-managed, packet-based power distribution at the voltages and power levels FMP enables. Article 726 fills that gap by:
- Defining Class 4 power sources and their required listed-equipment status.
- Establishing conductor and cable requirements specific to Class 4 systems.
- Setting separation and installation rules distinct from NEC Chapters 1 through 3.
- Clarifying relationships between Class 4 wiring and other wiring systems in the same space.
Relaxed Wiring-Method Requirements
One of the most operationally significant changes Article 726 introduces is the allowance to install Class 4 cable without conduit in most situations — a departure from the conduit and raceway requirements that govern conventional power wiring under NEC Chapters 3. Because the fault-managed source renders the cable touch-safe under fault conditions, the code treats Class 4 conductors more like low-voltage signal cabling than like branch-circuit power wiring. This translates directly into lower material costs, reduced labor, and faster deployment, particularly in data centers, edge sites, and retrofit environments where conduit routing is expensive or impractical.
Listed Equipment and Cable Requirements
Article 726 requires that both the power-source equipment and the cable be specifically listed for Class 4 use. Equipment must be listed to UL 1400-1, the standard covering Class 4 Fault-Managed Power Systems equipment. Cables must be listed to UL 1400-2 (currently an UL Outline of Investigation governing Class 4 cables). Off-the-shelf power or data cables do not qualify; only cable that has undergone the UL 1400-2 listing process may be used in a compliant Article 726 installation.
Capabilities and Infrastructure Implications
FMP systems are capable of operating at higher DC voltages than traditional Class 2 or Class 3 circuits, enabling meaningful power delivery over long cable runs — an attribute particularly valuable for distributed antenna systems, edge computing nodes, building automation endpoints, and remote data-center racks. Heather Technologies partner VoltServer publishes representative performance figures for its Digital Electricity transmitter channels; specific per-product voltage, wattage, and distance values should be confirmed directly against current VoltServer product documentation [FLAG: see FLAGS section].
Multiple transmitter channels can be run in parallel to serve higher-power loads, and standard data-type cabling can be used where it meets UL 1400-2 listing requirements — potentially leveraging existing structured-cabling pathways. The combination of long reach and relaxed conduit requirements makes FMP compelling for hyperscale and AI-density environments where copper quantity, weight, and installation complexity are significant cost drivers.
FMP in the Data Center: The DCPacket Titan Platform
Heather Technologies partner DCPacket applies Article 726-compliant FMP to data-center power distribution through its Titan Platform. Working in conjunction with VoltServer technology (formalized in a partnership announced December 2025), DCPacket targets the high-density power distribution challenges of AI infrastructure and hyperscale deployments — reducing conduit runs, copper mass, and installation time relative to conventional branch-circuit distribution.
Comparison: Class 4 vs. Traditional Low-Voltage Circuit Classes
| Attribute | Class 2 / Class 3 (Article 725) | Class 4 FMP (Article 726) |
|---|---|---|
| Governing NEC Article | 725 | 726 (2023 NEC) |
| Safety mechanism | Inherently limited energy / overcurrent protection | Packet-based fault detection, millisecond shutoff |
| Touch-safe under fault | By energy limitation | By active fault-managed source response |
| Conduit generally required | No (for Class 2/3 cable) | No (Article 726 allows installation without conduit in most cases) |
| Listed equipment standard | Varies by application | UL 1400-1 (source); UL 1400-2 (cable) |
| Voltage / power range | Strictly limited by NEC table | Higher DC voltages enabled by active fault management [FLAG] |
Adoption and Compliance Considerations
Because Article 726 was introduced in the 2023 NEC, its enforceability in any given jurisdiction depends on whether that jurisdiction has adopted the 2023 edition. Specifiers and installers should verify the locally adopted NEC edition before designing a Class 4 system. Where the 2023 NEC has not yet been adopted, FMP installations may require alternative approval pathways such as special inspection or engineering review.
All Class 4 installations must use source equipment listed to UL 1400-1 and cable listed to UL 1400-2. These listing requirements are not optional; they are the mechanism by which Article 726's relaxed wiring-method allowances are justified under the NEC's overall safety framework. Heather Technologies and its FMP partners can assist specifiers in identifying compliant equipment configurations for specific project requirements.