13.3 Class 1, Class 2 & Class 3 Power-Limited Circuits (Articles 724 & 725)
Key Takeaways
- The 2023 NEC relocated Class 1 circuit requirements out of Article 725 into a new Article 724, leaving Article 725 to cover only Class 2 and Class 3 power-limited circuits.
- NEC 724.40 limits a Class 1 power-limited circuit to 30 volts and 1,000 volt-amperes, supplied by a power source having a rated output not exceeding those values.
- Class 2 circuits are limited by the listed power source to levels considered safe from both a shock and a fire-initiation standpoint, while Class 3 circuits permit higher levels at which a shock hazard exists, so Class 3 wiring requires additional safeguards.
- NEC 725.136 generally prohibits Class 2 and Class 3 conductors from occupying the same cable, cable tray, enclosure, or raceway as electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband conductors, subject to specific exceptions such as a permanent barrier or a listed 0.25-inch separation.
- The 2023 NEC added Article 726 for Class 4 fault-managed power systems, which achieve touch safety through continuous monitoring and millisecond fault interruption rather than through inherent power limitation.
13.3 Class 1, Class 2 & Class 3 Power-Limited Circuits (Articles 724 & 725)
Exam Focus: The 2023 reorganization of Articles 722/724/725/726, the Class 1 30 V / 1,000 VA limit, Class 2 versus Class 3, listed power sources, 725.136 separation, cable types and substitutions, and abandoned cable removal.
The PSI bulletin names power limited circuits as a tested subject, and the statutory military-affidavit list in MCL 339.5715(1)(b)(ix) describes exactly this material: "circuits and equipment characterized by usage and electrical power limitations, including differentiating them from electric light and power circuits."
The 2023 Reorganization — Learn the New Article Numbers
If you trained on the 2017 or 2020 NEC, everything you know as "Article 725" has been split up.
| Article | 2023 NEC Scope |
|---|---|
| 722 | Cables for power-limited circuits, fault-managed power circuits, optical fiber, and communications circuits |
| 724 | Class 1 power-limited circuits and Class 1 power-limited remote-control and signaling circuits |
| 725 | Class 2 and Class 3 power-limited circuits |
| 726 | Class 4 fault-managed power systems (entirely new) |
A former "non-power-limited Class 1 remote-control and signaling circuit" is, technically, a branch circuit; because branch circuits are covered by Chapters 1 through 4, the 2023 NEC does not carry those requirements in Article 724.
Why These Circuits Get Their Own Rules
An ordinary branch circuit is protected by limiting the conductor: pick a wire, then pick an overcurrent device that protects it. A power-limited circuit is protected by limiting the source. Because the listed power source physically cannot deliver enough energy to start a fire or deliver a dangerous shock, the code relaxes the wiring method rules — smaller conductors, no raceway requirement, no derating.
+-------------------------------------------------------------------------+
| THE FOUR CLASSES AT A GLANCE (2023 NEC) |
| |
| CLASS 1 (Art. 724) 30 V and 1000 VA maximum |
| Usage and power limited; wiring methods are |
| closer to power circuits than Class 2/3. |
| |
| CLASS 2 (Art. 725) Limited by a LISTED power source to levels |
| considered safe from BOTH shock and fire. |
| Thermostats, doorbells, intercoms, PoE. |
| |
| CLASS 3 (Art. 725) Higher permitted levels than Class 2; a SHOCK |
| hazard can exist, so additional safeguards |
| apply to the wiring, but fire risk stays low. |
| |
| CLASS 4 (Art. 726) Fault-managed power. Higher voltage, made |
| touch-safe by continuous monitoring and |
| millisecond fault interruption. |
+-------------------------------------------------------------------------+
Class 1 Circuits — Article 724
- 724.40: Class 1 circuits are limited to 30 volts and 1,000 volt-amperes, and the power source must have a rated output not exceeding those limits.
- 724.43: Class 1 circuit conductors are protected against overcurrent, generally at their ampacity without applying 310.15(B) or (C) adjustment.
- 724.45: Overcurrent devices must be at the point of supply, with permitted tap arrangements and locations similar in spirit to the feeder tap rules.
- 724.46: Class 1 wiring methods follow Chapters 1 through 4 — this is the biggest practical difference from Class 2 and Class 3.
- 724.48: Class 1 circuits may occupy the same cable, cable tray, enclosure, or raceway with power supply conductors only where the equipment powered is functionally associated.
- 724.49: conductors of 18 AWG and 16 AWG are permitted where they do not supply loads greater than those specified in 724.49(A) and are installed in a raceway, approved enclosure, or listed cable.
Class 2 and Class 3 Circuits — Article 725
Power Sources
Class 2 and Class 3 circuits must be supplied by a listed Class 2 or Class 3 power supply, a listed information technology equipment limited-power circuit, a listed audio amplifier, a listed device with a Class 2 or Class 3 output, or a dry-cell battery within the limits. The permitted voltage, current, and volt-ampere combinations are tabulated in Chapter 9, Tables 11(A) and 11(B) — alternating current and direct current respectively. Those tables are in your code book; you do not memorize them.
Separation From Power Conductors — NEC 725.136
The general rule: Class 2 and Class 3 conductors must not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband communications circuits.
Selected permitted arrangements:
- Where the power-limited conductors are separated by a barrier from the power conductors;
- In enclosures where power conductors are introduced solely to connect the equipment connected to the Class 2 or Class 3 circuits, and a minimum of 6 mm (0.25 in) separation is maintained;
- In a manhole where the power conductors are in a metal-enclosed cable or Type UF, or a firmly fixed nonconductor is used, or the conductors are permanently and effectively separated;
- Where the Class 2 or Class 3 conductors are reclassified and installed as Class 1 circuits, in which case they must follow Class 1 rules entirely.
[!CAUTION] Reclassification is a one-way door. Class 2 or Class 3 wiring reclassified as Class 1 must comply with Article 724 in full — Chapter 3 wiring methods, overcurrent protection, and the works. Marking is required, and the cable can no longer be identified as CL2 or CL3.
Cable Types and Substitutions
| Type | Where Used |
|---|---|
| CL2P / CL3P | Plenum — ducts, plenums, and other environmental air spaces |
| CL2R / CL3R | Riser — vertical runs penetrating more than one floor, or in a shaft |
| CL2 / CL3 | General purpose |
| CL2X / CL3X | Limited use — dwellings and raceways |
The substitution hierarchy runs downward: a plenum cable may be used anywhere; a riser cable may be used for general purpose but not in a plenum; a general-purpose cable may not be used in a riser or plenum. Type CL3 may substitute for CL2 (it is the more robust listing), but CL2 may not substitute for CL3.
Installation Requirements Common to Article 725
- Mechanical execution of work: cables must be installed in a neat and workmanlike manner, supported by the building structure so the cable is not damaged by normal building use, and not secured to or supported by a raceway (300.11(C)).
- Abandoned cables: the accessible portion of abandoned Class 2, Class 3, and PLTC cable must be removed. An abandoned cable is one not terminated at equipment and not identified for future use with a tag.
- Ampacity: where Class 2 or Class 3 circuits deliver power to equipment such as Power over Ethernet, ampacity and bundling limits apply based on the conductor size and the number of cables in a bundle.
Class 4 Fault-Managed Power — Article 726 (New in 2023)
Article 726 recognizes systems in which the source continuously monitors the energy it delivers and interrupts delivery in milliseconds when a fault is detected. That active management, rather than inherent power limitation, is what makes the system touch-safe at voltages well above the Class 2 and Class 3 thresholds. The article covers Class 4 power sources, loads, marking, terminals and connectors, and separation from other circuits.
Under the 2023 NEC, which article covers Class 1 power-limited circuits and Class 1 power-limited remote-control and signaling circuits?
What are the maximum voltage and volt-ampere limits for a Class 1 power-limited circuit under NEC 724.40?
Class 2 cable is run into a junction box that also contains 120-volt branch-circuit conductors, and no barrier is present. What does NEC 725.136 require?
Which cable substitution is permitted for power-limited circuits?