UL 924: Emergency Lighting & Power Equipment
Safety standards for emergency lighting systems, inverters, and power equipment
Overview
UL 924 is the Standard for Safety for Emergency Lighting and Power Equipment, establishing requirements for emergency lighting equipment, unit equipment for emergency lighting, exit signs, and emergency power supply systems. This standard ensures reliable operation during power failures and provides the safety requirements for emergency lighting systems in commercial and institutional buildings.
Code Compliance: UL 924 listed equipment is required by most building codes including the IBC, IFC, and NFPA 101 Life Safety Code. Equipment must be listed by a nationally recognized testing laboratory (NRTL) to meet code requirements for emergency lighting systems.
The standard covers construction, performance, and testing requirements for emergency lighting equipment including luminaires, battery packs, inverters, generators, and central battery systems. All components must provide reliable illumination for a minimum of 90 minutes during normal AC power interruption.
Equipment Types & Categories
Emergency Lighting Equipment
- Self-Contained Units: Battery backup luminaires with integral charging circuit and battery
- Remote Head Systems: Central battery pack powering multiple remote lamp heads
- Central Battery Systems: Large battery systems serving multiple emergency lights
- Generator Systems: Engine-driven generators with automatic transfer equipment
Exit Sign Categories
- Internally Illuminated: LED or incandescent exit signs with backup battery
- Externally Illuminated: Signs illuminated by separate emergency lighting
- Photoluminescent: Self-luminous signs charged by ambient lighting
- Edge-Lit Signs: LED technology with light guides for uniform illumination
Power Equipment Types
- Emergency Lighting Inverters: Static inverters providing AC power from battery DC
- Transfer Switches: Automatic switching between normal and emergency power
- Battery Chargers: Charging equipment for emergency lighting batteries
- Control Panels: Monitoring and control equipment for emergency systems
Installation Requirements
General Installation Standards
- Mounting Heights: 7 feet minimum to bottom of fixture for vandal resistance
- Environmental Ratings: Appropriate IP rating for installation location (dry, damp, wet)
- Temperature Ranges: Equipment rated for ambient temperature conditions
- Circuit Protection: Dedicated circuit with appropriate overcurrent protection
- Accessibility: Test switches and indicators readily accessible for maintenance
Wiring & Electrical Requirements
- Installation per NEC Article 700 (Emergency Systems)
- Emergency circuits separated from normal lighting circuits
- Fire-rated wiring systems where required by code
- Proper grounding and bonding of emergency equipment
- Transfer time of 10 seconds maximum for emergency lighting
Performance Standards
| Performance Metric | Requirement | Test Condition |
|---|---|---|
| Emergency Duration | 90 minutes minimum | Full load, 77°F ambient |
| Illumination Level | 1 footcandle average | At floor level, egress path |
| Transfer Time | 10 seconds maximum | From AC failure to emergency |
| Recharge Time | 24 hours maximum | To 90% capacity after discharge |
| Exit Sign Visibility | 100 feet maximum | Clear viewing distance |
Battery Performance Requirements
- Service Life: Minimum 5 years for sealed lead-acid, 10 years for nickel-cadmium
- Temperature Range: Operating from 32°F to 104°F for most battery types
- Capacity Testing: Annual discharge tests to verify 90-minute duration
- Voltage Regulation: Maintain rated voltage within ±10% during discharge
Testing Procedures
Monthly Testing Requirements
- 30-second illumination test to verify operation
- Visual inspection for physical damage or obstructions
- Test activation of manual test switches
- Verify LED indicator status (normal/charging)
- Document test results and any deficiencies
Annual Testing Requirements
- 90-minute full discharge test at full rated load
- Measure illumination levels at required locations
- Verify automatic transfer operation timing
- Test recharge time to 90% capacity
- Battery replacement when failing capacity tests
Maintenance Requirements
Routine Maintenance Tasks
- Clean lenses and reflectors to maintain light output
- Check and tighten electrical connections annually
- Replace lamps when light output drops below requirements
- Replace batteries when capacity falls below 90%
- Maintain manufacturer documentation and test records
Replacement Schedules
- LED Lamps: 15-20 years typical service life
- Sealed Lead-Acid Batteries: 3-5 years depending on conditions
- Nickel-Cadmium Batteries: 8-12 years with proper maintenance
- Transfer Switches: 20+ years with regular inspection
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