NFPA 110: Level 1 vs Level 2 Emergency Power Systems
Standards for generators, transfer switches, and emergency power supply systems
Last updated: May 4, 2026
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Overview
NFPA 110 is the standard for emergency and standby power supply systems (EPSS): the rules for how generators, transfer switches, and fuel systems must be installed, tested, and maintained. It classifies systems as Level 1 (failure could cause loss of life) or Level 2 (less critical), and sets the testing schedule, fuel storage capacity, and room separation requirements. NFPA 110 does not decide which buildings need emergency power, that comes from NFPA 101, NFPA 99, or local building codes.
Critical Note: NFPA 110 does not determine which facilities require emergency power. Those requirements come from NFPA 101 (Life Safety Code), NFPA 99 (Healthcare Facilities), and local building codes. NFPA 110 specifies how to properly install and maintain the systems once required.
The standard applies to permanently installed emergency and standby power systems including generators, transfer equipment, controls, supervisory equipment, and associated electrical and mechanical auxiliary systems.
Level, Type, and Class Classifications
NFPA 110 uses three parameters to classify Emergency Power Supply Systems:
Level - Application Criticality
- Level 1: Where failure could result in loss of human life or serious injuries
- Level 2: Where failure is less critical to human life and safety
Type - Restoration Time
| Type | Restoration Time | Typical Application |
|---|---|---|
| Type U | Uninterruptible (UPS) | Critical computer systems |
| Type 10 | 10 seconds | Emergency lighting, life safety |
| Type 60 | 60 seconds | Less critical systems |
| Type 120 | 120 seconds | Equipment protection |
| Type M | Manual (no time limit) | Portable generators |
Class - Runtime Duration
- Class 0.083: 5 minutes (UPS systems)
- Class 0.25: 15 minutes
- Class 2: 2 hours
- Class 6: 6 hours
- Class 48: 48 hours
- Class X: Other time as required (typically 72-96 hours)
Level 1 vs Level 2 Requirements
Level 1 Systems (Life Safety Critical)
- Emergency lighting for means of egress
- Fire detection and alarm systems
- Fire pumps
- Elevators for high-rise buildings
- Critical ventilation systems (smoke control)
- Healthcare facility critical branches
- Emergency communication systems
Level 2 Systems (Less Critical)
- Heating and refrigeration systems
- Communication systems (non-emergency)
- Sewage disposal
- Industrial processes
- Data processing systems
Key Differences in Requirements
| Requirement | Level 1 | Level 2 |
|---|---|---|
| Fuel Storage | 96 hours typical | As specified |
| Testing Frequency | Weekly/Monthly | Monthly |
| Room Separation | 2-hour fire rating | 1-hour typical |
| Temperature Control | 40°F minimum | Per manufacturer |
System Components
A complete EPSS includes these essential components:
Energy Converters (EPS)
- Prime Mover: Diesel, natural gas, or bi-fuel engines
- Generator: Alternator producing electrical power
- Cooling System: Radiator or heat exchanger
- Exhaust System: Mufflers and emissions controls
- Starting System: Batteries and charging system
Transfer Equipment
- Automatic Transfer Switch (ATS): Transfers load between normal and emergency power
- Bypass Isolation Switch: Allows ATS maintenance without interruption
- Load Bank Connection: For testing without building load
- Paralleling Gear: For multiple generator systems
Controls and Annunciation
- Local and remote annunciator panels
- Automatic starting controls
- Battery monitoring systems
- Remote monitoring capabilities
- Load management controls
Fuel Systems & Storage
Fuel Storage Requirements
- Main Tank Capacity: 133% of required runtime (safety factor)
- Day Tank: 1 hour minimum supply at full load
- Fuel Transfer: Automatic refill from main tank
- Fuel Quality: ASTM-compliant diesel or natural gas
- Fuel Polishing: Recommended for long-term storage
- Natural Gas: Dual fuel connections where available
Fuel System Components
- Fuel Pumps: Redundant pumps for Level 1 systems
- Filters: Primary and secondary filtration
- Water Separators: Remove moisture from fuel
- Fill Connections: Accessible for emergency refueling
- Fuel Polishing: Recommended for long-term storage
- Natural Gas: Dual fuel connections where available
Generator yard spill response. NFPA 110 sets the performance and storage rules for the EPSS itself. The complementary spill-response equipment (drum spill pallets, oil-only sorbents, drip pans, drain covers) and the EPA SPCC eligibility test (1,320-gallon aboveground threshold) live alongside it. See Data Center Support-Area Safety for the generator-yard checklist.
Testing & Maintenance Requirements
| Test Type | Level 1 Frequency | Duration | Load Requirements |
|---|---|---|---|
| No-Load Test | Weekly | 5-10 minutes | None |
| Monthly Test | Monthly | 30 minutes | Available load |
| Annual Test | Annual | 4 hours | 100% nameplate |
| Triennial Test | 36 months | 4 hours | With load bank |
| Transfer Test | Monthly | Complete cycle | Actual loads |
Maintenance Requirements
- Weekly Inspection: Visual check of all systems
- Oil & Filter Changes: Per manufacturer or oil analysis
- Coolant System: Annual flush and refill
- Battery Maintenance: Monthly specific gravity tests
- Fuel Testing: Annual quality testing
- Documentation: Written logs of all tests and maintenance
Installation Requirements
Location & Environment
- Indoor Installation: Separate room with proper ventilation
- Fire Rating: 2-hour separation for Level 1 systems
- Temperature: Maintain minimum 40°F (Level 1), 32°F (Level 2)
- Ventilation: Combustion air and cooling requirements
- Working Space: 3 feet minimum around equipment
- Outdoor Installation: Weather enclosures meeting Type ratings
Electrical Installation
- Separate feeders for emergency loads
- Proper grounding and bonding systems
- Surge protection devices
- Selective coordination of overcurrent devices
- Remote annunciator in attended location
- Integration with building management systems
Frequently Asked Questions
What is NFPA 110?
NFPA 110 is the Standard for Emergency and Standby Power Systems. It sets the installation, testing, and maintenance requirements for emergency power supply systems (EPSS), including generators, transfer switches, fuel systems, and controls. NFPA 110 does not determine which buildings require emergency power. That decision comes from NFPA 101 (Life Safety Code), NFPA 99 (Healthcare Facilities), and local building codes. The current edition is NFPA 110-2025.
What is the difference between NFPA 110 Level 1 and Level 2?
Level 1 systems serve loads where failure could cause loss of human life or serious injury, such as emergency lighting on means of egress, fire alarm, fire pumps, and high-rise elevators. Level 2 systems serve less critical loads such as heating, sewage disposal, and industrial processes. Level 1 has stricter rules: longer fuel storage, more frequent testing, 2-hour fire-rated room separation, and a 40 degrees F minimum room temperature. Level 2 typically requires 1-hour separation and monthly testing.
Can unrelated systems share the life safety generator room?
No. NFPA 110 requires the EPS room to be dedicated to the emergency power supply system and its directly supporting equipment. Equipment unrelated to the EPSS, such as building HVAC equipment, normal-power switchgear, or general-purpose storage, is not permitted in the same room. The separation rule protects the generator from a fire or failure originating in unrelated systems and keeps the room clear for testing and service access.
What is the NFPA 110 load bank testing requirement?
Level 1 generators that fail to reach 30 percent of nameplate kW during a monthly test must run an annual load bank test for 4 hours: 30 minutes at 25 percent, 30 minutes at 50 percent, and 3 hours at 75 percent of nameplate kW. Every 36 months, all Level 1 generators (regardless of monthly load) must run a triennial load bank test for 4 hours at full nameplate kW. Document every test in writing and keep records for the life of the system.
NFPA 110 Compliant Products
We don't have a curated product set for NFPA 110 yet. Search the catalog or browse related categories.
Search the catalogRelated Standards
Fire alarm systems require emergency power backup per NFPA 72 Fire Alarm Code. Fire pump controllers covered under NFPA 13 Sprinkler Systems also require emergency power connections.
For generator testing and inspection requirements by jurisdiction, see our Fire Inspection & Compliance Guide.
Hospitals, nursing homes, and ambulatory care facilities carry additional emergency-power obligations under CMS surveys and NFPA 99. See our sister site's healthcare fire-protection compliance overview.
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