21.2 Class 4 Fault-Managed Power, Tray Cables, Fire-Resistive Cable Systems & Limited-Energy Grounding (Articles 726, 727, 742, 750 & 772)
Key Takeaways
A Class 4 fault-managed power system consists of a listed Class 4 power transmitter and power receiver connected by a Class 4 cabling system, with the transmitter monitoring the circuit for faults and limiting the energy delivered into a fault (Article 726).
Class 4 cables are marked CL4P for plenums, CL4R for risers, and CL4 for general use (Article 722).
The 2026 NEC 700.28 allows Class 4 fault-managed power to supply emergency lighting where it is listed for emergency use and integrated into an emergency lighting system.
Type ITC instrumentation tray cable is limited to circuits of 150 V or less and 5 A or less, in industrial establishments with qualified maintenance (Article 727).
A fire-resistive cable system must be installed exactly as its listing describes, including supports, raceways, fittings, and splices, to keep its fire rating (Article 772, formerly Article 728).
Class 4 fault-managed power (Article 726)
Class 4, introduced in the 2023 NEC, delivers power levels well above Class 2 over limited-energy cabling. Instead of limiting power at all times, a Class 4 power transmitter continuously monitors the circuit and the power receiver, and it shuts the power off within milliseconds if it detects a short circuit, a person touching the conductors, or other abnormal conditions. Typical uses include LED lighting, building systems, and telecommunications equipment fed over long cable runs.
| Rule | Requirement |
|---|---|
| Components | A listed Class 4 power transmitter, a listed Class 4 power receiver (or listed utilization equipment with an integral receiver), and a Class 4 cabling system |
| Power source | The transmitter output is limited to 450 V peak or dc; transmitters and receivers are listed together as a system and marked with their maximum output voltage and current and the receivers and cables they are for |
| Cables | Listed CL4P (plenum), CL4R (riser), or CL4 (general purpose), or permitted substitutes, installed per Articles 720 and 722 |
| Marking | Class 4 equipment and cables are marked as Class 4; the transmitter's output must be identified |
| Separation | Class 4 conductors are kept separate from power, Class 1, and nonpower-limited fire alarm conductors, following the same principles as Class 2 and 3 circuits |
| Not permitted | In hazardous locations except where specifically permitted, and where the listing does not cover the environment |
| Emergency lighting (2026, 700.28) | Class 4 may supply emergency lighting where it is listed for emergency use and integrated into the emergency lighting system |
Because a Class 4 system depends on its electronics for safety, it must be installed exactly as listed, and only listed receivers may be connected.
Power-limited and instrumentation tray cables
| Cable | Article | Key rules |
|---|---|---|
| PLTC (power-limited tray cable) | 725 | For Class 2 and Class 3 circuits; permitted in cable trays, raceways, supported by messenger wire, and direct buried where identified; in industrial establishments with qualified maintenance, PLTC may run exposed between a cable tray and equipment for up to 50 ft if protected and supported |
| ITC (instrumentation tray cable) | 727 | Instrumentation and control circuits of 150 V or less and 5 A or less, in industrial establishments where qualified persons service the system; in cable trays, raceways, hazardous locations as permitted, and exposed between tray and equipment for limited distances |
| ITC-HL | 727 and 501 | Hazardous-location version with a gas- and vapor-tight continuous corrugated metallic sheath, used in Class I, Division 1 industrial locations with listed fittings |
Raceways and cable routing assemblies (Article 723)
Limited-energy cables may be installed in raceways, in cable routing assemblies (open-channel pathway systems), and in cable trays. These systems are rated like cables: plenum, riser, and general-purpose, and must be installed in spaces matching their rating.
Overvoltage protection (Article 742, new in 2026)
Article 742 collects the requirements for protecting limited-energy systems from lightning and power-line surges, such as primary protectors on communications circuits entering buildings and surge protective devices on limited-energy equipment. Protectors must be listed and installed where the circuit enters the building, with short, straight bonding conductors.
Grounding and bonding (Article 750, new in 2026)
Article 750 collects the grounding and bonding rules for limited-energy systems that were scattered through Articles 725, 760, 770, 800, and 820:
- Metallic cable shields and protectors of circuits entering a building are bonded to the building's grounding electrode system, usually at the intersystem bonding termination (IBT) required by 250.94.
- The bonding conductor is copper, insulated, at least 14 AWG, run as straight and short as practicable; at one- and two-family dwellings it may not exceed 20 ft in length (or a separate electrode bonded to the power electrode system is required).
- Separately installed electrodes for communications must be bonded to the power grounding electrode system with at least 6 AWG copper.
Fire-resistive cable systems (Article 772, formerly Article 728)
A fire-resistive cable system is a listed cable and its listed accessories that maintain circuit integrity for a specified time, usually 2 hours, during a fire. They are used for emergency feeders, fire pump feeders, and fire alarm survivability circuits where other codes require circuit integrity.
- The system must be installed exactly as the listing describes, including the cable, the type and spacing of supports, any raceway and its fittings, splices, pulling lubricants, and vertical supports.
- Supports and raceways must have the fire rating the listing requires; ordinary straps can fail in a fire and drop the cable.
- Cables are marked with the fire-resistive rating and the system's listing designation, and splices are permitted only as the listing allows.
Worked example: an LED lighting retrofit on Class 4
A building owner installs Class 4 power to LED fixtures throughout an office floor.
- Equipment: a listed Class 4 transmitter in the IT room, listed Class 4 receivers at each fixture zone.
- Cable: CL4P in the return-air plenum above the ceiling, supported by the structure.
- Separation: keep the Class 4 cables out of the raceways and boxes that contain 277 V lighting branch circuits.
- Emergency lighting: if some fixtures serve as emergency lighting, the Class 4 system must be listed for emergency use and integrated into the emergency lighting system (2026 NEC 700.28).
What makes a Class 4 fault-managed power system safe at higher power levels?
The transmitter monitors the circuit and shuts off power on a fault
The cable is always installed in rigid metal conduit for protection
The output voltage never exceeds 30 V under any condition
Each circuit is GFCI protected
What are the voltage and current limits for Type ITC instrumentation tray cable circuits under Article 727?
30 V and 1 A
600 V and 20 A
1000 V and 10 A
150 V and 5 A
A contractor installs a listed 2-hour fire-resistive cable system for an emergency feeder. What determines how it must be supported?
General NEC support spacing for the raceway type only
The system's listing, including supports, raceways, and fittings
The building's seismic bracing code only
The installer's preference, if all supports are galvanized steel
Sections you finish are checked off in the contents.