Class 4 Fault-Managed Power: What Low Voltage Contractors Need to Know

There's a new player in the low voltage world, and it could change how we think about power delivery: Class 4 fault-managed power systems. First introduced in NEC 2023 and expanded in NEC 2026, Class 4 enables power delivery at levels previously reserved for line-voltage work—but with the installation simplicity of limited-energy systems.

If you're installing PoE devices, thinking about digital electricity, or wondering why everyone's talking about "fault-managed power," this guide explains what you need to know.

What is Class 4 Power?

Class 4 is a circuit classification in the NEC that describes fault-managed power systems (FMPS). Unlike traditional limited-energy circuits that restrict total output, Class 4 systems:

• Can deliver hundreds or thousands of watts
• Operate at voltages up to 450V AC or DC
• Use intelligent monitoring to limit energy into a fault
• Allow installation using limited-energy wiring methods

The key innovation: Instead of limiting power at the source, Class 4 systems continuously monitor the circuit and instantly shut down if they detect a fault condition—whether that's a short circuit, an arc, or human contact.

How Class 4 Differs from Class 2 and Class 3

Characteristic	Class 2	Class 3	Class 4
Power limited at source	Yes	Yes	No
Fault-managed	No	No	Yes
Max voltage	30V typical	100V typical	450V
Max power	100VA typical	Higher	Unlimited*
Shock hazard	Minimal	Low	Managed
Fire hazard	Minimal	Low	Managed
Installation methods	Limited energy	Limited energy	Limited energy

*Class 4 power is unlimited at the source but limited into any fault condition.

The Technology Behind Fault-Managed Power

Class 4 systems work through continuous monitoring and rapid response:

How It Works

1. Power transmitter sends power over the cable
2. Continuous monitoring checks for fault conditions
3. Fault detection identifies shorts, arcs, or contact
4. Rapid shutdown limits energy into the fault (<1ms typical)
5. Safe restart once fault is cleared

What Gets Detected

• Human contact - System detects impedance change
• Short circuits - Sudden current increase
• Arc faults - Characteristic electrical signature
• Cable damage - Changes in line characteristics

Why This Matters

Traditional power limiting restricts what you can do with a circuit. A Class 2 circuit maxes out around 100VA—fine for sensors and controls, but not for powering displays, access control hardware, or LED lighting.

Class 4 removes this limitation while maintaining safety through intelligent management.

Article 726: NEC Requirements

Class 4 systems are governed by Article 726 in the NEC.

Key Requirements

726.1 Scope
Covers installation of wiring systems and equipment for Class 4 fault-managed power systems.

726.4 Equipment Listing

• Class 4 transmitters must be listed
• Class 4 receivers must be listed
• Cabling systems must be listed for Class 4 use

726.5 Connectors
Connectors for Class 4 circuits SHALL NOT be interchangeable with non-power-limited sources on the same premises. This prevents accidental connection of Class 4 cabling to traditional power.

726.6 Separation
Requirements for separation from:

• Electric light and power circuits
• Class 1 circuits
• Non-power-limited fire alarm
• Medium-power network-powered broadband

726.7 Grounding
Grounding and bonding requirements specific to Class 4 systems.

Real-World Applications

Power over Ethernet (PoE) Evolution

PoE has progressed through several standards:

Standard	Power	Typical Use
802.3af (PoE)	15.4W	IP phones, basic cameras
802.3at (PoE+)	30W	PTZ cameras, access points
802.3bt (PoE++)	60-90W	Video displays, door controllers
Class 4 FMPS	100W+	LED lighting, larger displays

Class 4 enables the next generation of PoE—powering devices that previously required separate electrical circuits.

Digital Electricity

Systems marketed as "digital electricity" or "packet energy transfer" often use Class 4 principles:

• Power delivered in controlled pulses
• Continuous safety monitoring
• Higher voltages for efficiency (less copper needed)
• Integration with smart building systems

Specific Use Cases

Lighting

• LED fixtures powered over Category cable
• Simplified installation vs. traditional wiring
• Integrated controls and monitoring

Displays and Signage

• Digital signage without separate power drops
• Video walls with single cable runs
• Interactive displays in commercial spaces

Access Control

• High-power door hardware (electric strikes, maglocks)
• Integrated power and data
• Reduced wiring complexity

Workstations

• Desk power delivery over structured cabling
• Rapid reconfiguration without electrical work
• Metered, managed power per workspace

Installation Considerations

Cable Requirements

Class 4 systems require cables listed for fault-managed power use. Not all Category cable qualifies:

• Check for Class 4/FMPS listing
• Verify voltage rating
• Confirm with transmitter manufacturer
• Document cable specifications for inspection

Connector Compatibility

The non-interchangeability requirement (726.5) means:

• Standard RJ-45 may not be appropriate
• Proprietary connectors may be required
• Clear labeling of Class 4 circuits
• Separation from standard network infrastructure

Transmitter/Receiver Pairing

Class 4 systems are typically proprietary:

• Transmitter and receiver from same manufacturer
• Specific cable requirements
• Listed as a complete system
• Follow manufacturer installation guidelines

Inspection Points

Inspectors will verify:

• Listed equipment (transmitter, receiver, cables)
• Proper connector types
• Separation from power circuits
• Labeling and documentation
• Compliance with Article 726

Business Opportunities

New Revenue Streams

Class 4 creates opportunities for low voltage contractors:

1. LED lighting installation - Previously electrical contractor territory
2. Desktop power delivery - Corporate reconfiguration projects
3. Digital signage - Simplified installation wins bids
4. Smart building integration - Power and data convergence

Competitive Advantages

• Faster installation than traditional wiring
• Lower total project cost
• Flexibility for future changes
• Integration with existing network infrastructure

Training Requirements

To capture these opportunities:

• Manufacturer-specific training (often required for warranty)
• Understanding of Article 726 requirements
• Integration with existing structured cabling skills
• Familiarity with specific product platforms

Challenges and Limitations

Current Limitations

• Proprietary systems - Limited interoperability
• Cost - Transmitters/receivers more expensive than standard PoE
• Availability - Still emerging, not all applications covered
• Inspector familiarity - May face questions on new technology

Jurisdictional Questions

Some jurisdictions may question whether low voltage contractors can install Class 4 systems:

• Voltage levels exceed traditional "low voltage" thresholds
• May trigger electrical permit requirements
• Check with local AHJ before bidding

Technology Evolution

Class 4 is still maturing:

• Standards continue developing
• Products entering market
• Best practices establishing
• Code interpretations clarifying

Getting Started with Class 4

Education

1. Read Article 726 - Understand the code requirements
2. Manufacturer training - Required for most systems
3. Industry resources - BICSI, NECA publications
4. Code update courses - Include Class 4 in 2023/2026 updates

Small Project Experience

Before bidding large Class 4 projects:

• Install a demonstration system
• Work with manufacturer support
• Document lessons learned
• Build inspector relationships

Strategic Positioning

Position your company for Class 4 opportunities:

• Market as technology-forward
• Highlight power + data convergence capabilities
• Develop relationships with Class 4 equipment vendors
• Track permit activity for applicable projects

The Future of Class 4

Industry Trajectory

Class 4 is positioned to grow as:

• Smart building adoption increases
• Energy management demands rise
• Installation labor costs push toward efficiency
• Technology improves and costs decrease

NEC Evolution

Expect continued development:

• NEC 2026 expanded Class 4 provisions
• NEC 2029 likely to refine further
• More products entering market
• Inspection practices standardizing

Your Opportunity

Low voltage contractors who master Class 4 early will have competitive advantages as the technology matures. The convergence of power and data continues—those who can deliver both will win.

Stay Ahead of Emerging Technology

Class 4 projects are appearing in permit systems now. Get early intelligence on opportunities.

LVN Signal monitors permit activity and alerts you to projects before they hit bid boards.

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Last updated: January 2026. Class 4 technology and code requirements are evolving. Consult current NEC and manufacturer documentation for specific installations.