Emergency Generator Testing and Maintenance (NFPA 110)

A summer storm drops utility power on a Friday evening. The generator starts, the transfer switch moves, and the exit lights and fire alarm panel stay on. Then the engine shuts down on a fault and the building goes dark with people still inside. The service log says the unit was “exercised, OK” every month. It does not say what load it carried, for how long, or whether the transfer switch was ever operated.

That log tells the fire marshal nothing. Emergency generator maintenance under the NFPA 110 requirements is two jobs: keep the system able to carry its load, and prove it with records an inspector will accept.

This guide covers when NFPA 110 applies, the weekly-to-36-month test calendar, transfer switches, fuel and batteries, the records an authority having jurisdiction (AHJ) asks for, and the part most guides skip: air permits and run-hour limits in Virginia, Maryland and DC. Levaru schedules and documents this work as part of our electrical services, with the regulated work done by licensed electricians and manufacturer-trained technicians. This is general guidance, not legal or engineering advice; your AHJ and air regulator have the final word.

Does NFPA 110 apply to your generator?

NFPA 110 applies when a code requires an emergency power supply system (EPSS) and points to the standard. The current edition is 2025, but your AHJ enforces the edition its adopted code references, which is often older.

The National Electrical Code sorts backup power into three groups:

• Emergency systems (NEC Article 700). Life-safety loads that codes require, such as egress lighting and fire alarm systems. Virginia’s fire code generally requires them to pick up load within 10 seconds.
• Legally required standby (Article 701). Loads whose loss could create hazards or hamper rescue or firefighting, such as smoke removal and ventilation. Virginia’s code generally sets a 60-second pickup.
• Optional standby (Article 702). Loads where life safety does not depend on the system: servers, refrigeration, tenant comfort. The 2025 edition of NFPA 110 states that it does not cover these systems.

Many buildings run one generator that feeds both kinds of load. NFPA’s technical committee has stated that a generator supplying both emergency and optional loads is an emergency power supply system, so the whole unit is maintained to NFPA 110. A high-rise with a fire pump or smoke control on generator power almost certainly has an EPSS; an office with a generator only for its server room may not. The electrical drawings show which panels are which.

What do Level, Type and Class mean?

NFPA 110 rates every EPSS three ways. The codes that require the system choose the ratings, not NFPA 110, and the design documents should record them.

Rating	What it means	Common values
Level 1	Failure could cause loss of life or serious injury	Egress lighting, fire alarm, fire pumps, elevators
Level 2	Failure is less critical to life safety	Ventilation, heating, communications
Type	Maximum seconds without power at the load	U (uninterruptible), 10, 60, 120, M (manual), X
Class	Minimum hours at rated load without refueling	0.083 (5 min), 0.25, 2, 6, 48, X

Level drives the test burden: Level 1 systems carry the 36-month test and stricter battery and breaker rules. Class drives fuel. NFPA’s own summary says the fuel supply must be sized at 133 percent of what the system needs for its Class duration, so a Class 6 system with a half-empty tank cannot deliver its rating.

What is the complete generator testing calendar?

The table combines NFPA 110 minimums with manufacturer-driven tasks (“Mfr.”). NFPA 110 itself says the program must rest on the manufacturer’s recommendations, the instruction manuals, the standard’s minimums and the AHJ’s requirements.

Interval	Task	Basis
Weekly	Inspect EPSS, transfer switches, Level 1 batteries	NFPA 110
Monthly	30-minute load run, transfer switch operation	NFPA 110
Monthly	Battery testing; Level 2 inspection (2025 ed.)	NFPA 110
Quarterly	Battery load test	NFPA guidance
Quarterly	Coolant, belts, hoses, exhaust checks	Mfr.
Semiannual	Oil, fuel and air filters by hours or time	Mfr.
Annual	Fuel quality test; Level 1 breaker exercise	NFPA 110
Annual	Diesel load bank test if monthly runs were light	NFPA 110
Annual	Full service, IR scan, ATS maintenance	Mfr., good practice
Every 36 months	Level 1 extended run, up to 4 hours	NFPA 110
After major repairs	30-minute run at operating temperature	NFPA 110

Put each line on your building compliance calendar against the actual unit and its last annual and 36-month test dates.

What does the weekly inspection cover?

The weekly inspection is a visual and functional check. It does not require running the engine, and NFPA 110’s annex warns that running an unloaded diesel during weekly checks can cause wet stacking.

A useful weekly round covers:

1. Control panel: no alarms, switch in automatic, hour meter recorded.
2. Leaks, plus oil, coolant, day tank and main tank levels.
3. Block heater on and holding temperature.
4. Battery charger in float, terminals clean and tight.
5. Transfer switches: no alarms, set to automatic.
6. Room or enclosure: louvers clear, no storage, exhaust path open.

Two edition details matter. The 2025 edition lets Level 2 systems move to a monthly visual inspection, but the NFPA 110 editions referenced by Virginia’s and DC’s adopted fire codes predate that change. Plan on weekly inspections for both levels unless your AHJ says otherwise in writing. And since the 2022 edition, automated monitoring can stand in for the weekly inspection of the equipment it actually monitors. It does not replace the monthly run.

How do you run the monthly load test correctly?

Run the generator at least monthly for at least 30 minutes under load. A diesel unit must either keep its exhaust at the manufacturer’s minimum temperature or carry at least 30 percent of its standby nameplate kW. Natural gas and other spark-ignited units run with the available EPSS load.

The 30 percent figure is where many programs fall short, because a building’s real life-safety load is often far below 30 percent of a generator sized for growth. Running light leaves unburned fuel and carbon in the exhaust, which is wet stacking. NFPA 110’s annex also warns that standby and prime ratings differ: a 100 kW standby set is usually an 80 kW prime set, so 30 percent is 30 kW on one rating and 24 kW on the other. Use the standby figure and keep it on file.

NFPA’s published procedure makes a good log template:

1. Record the hour meter.
2. Start from the transfer switch test switch or by opening the normal supply.
3. Record the start time delay and cranking time.
4. Transfer the load; record voltage, frequency, amps and kW.
5. After 15 minutes, record oil pressure, charging rate and coolant temperature.
6. After at least 30 minutes, retransfer and record the time delays.
7. Return the unit to automatic.

Each test should be a cold start. With several automatic transfer switches (ATSs), rotate which one starts the test. NFPA 110 sets minimum time delays of 1 second on start, 5 minutes before retransfer, and 5 minutes of cooldown. The owner picks the test time, so schedule around tenants: a transfer can briefly interrupt loads not on a UPS.

A real outage can count. NFPA 110 lets recorded standby use substitute for a scheduled test if you keep the same record a test would produce.

When are the annual load bank and 36-month tests required?

If a diesel unit’s monthly runs miss the 30 percent or exhaust temperature criterion, it still runs monthly with the available load. It then needs one supplemental load test each year: at least 50 percent of nameplate kW for 30 minutes, then at least 75 percent for 60 minutes, for 1.5 continuous hours. A portable load bank supplies the extra load, and it must drop off automatically if normal power fails during the test.

Level 1 systems also need an extended test at least once every 36 months. It runs for the Class duration, but may stop after 4 continuous hours. For diesel units the minimum load is the same criterion as the monthly test. The test starts at the transfer switches, and loads outside the EPSS do not have to lose power.

The tests can be combined. NFPA 110 lets one event count as a monthly test, the annual load bank test and the 36-month test, provided the first part runs at the minimum load and the last hour at 75 percent or more. That saves a load bank mobilization every third year.

How should transfer switches and breakers be tested?

Operate every transfer switch monthly by moving it electrically from normal to emergency and back. The monthly test does not have to prove the 10-second Type 10 time. If it does not, the standard calls for a process to confirm that capability once a year.

Maintenance keeps the switch healthy: NFPA 110 requires a program that checks connections, looks for overheating and contact erosion, removes dust and dirt, and replaces contacts when needed.

For Level 1 systems, the main and feeder breakers between the generator and the transfer switch load terminals are exercised once a year with the generator off. Medium-voltage breakers have separate, more demanding intervals.

This work belongs to a licensed electrician. Bundle it with the annual infrared scan of switchgear and panels described in our commercial electrical maintenance guide. NFPA 70B, which became a maintenance standard rather than a recommended practice in January 2023, is the reference for that broader electrical program.

What fuel, battery and engine work keeps a generator ready?

Fuel. NFPA 110 requires a fuel quality test at least annually, using applicable ASTM methods or the manufacturer’s recommendations. The annex advises testing from the first fill to set a benchmark, watching for water at the tank bottom, and testing for degradation and microbial growth. If fuel needs cleaning, treatment or replacement, retest every 90 days until results are acceptable. Fuel sitting in a tank that rarely turns over is the main concern.

Batteries. NFPA’s guidance calls battery failure the most common cause of generator failure. Level 1 starting batteries are inspected weekly; Level 2 batteries monthly under the 2025 edition. All are tested monthly. For batteries with access to the electrolyte, record specific gravity. For sealed batteries, use a conductance, ohmic, carbon pile or cranking voltage drop test. Replace a defective battery as soon as you find it.

Engine. Block heaters, coolant, belts, hoses, filters and oil follow the manufacturer’s manual. Older units also have a federal floor. An existing emergency diesel (construction began before June 12, 2006) at a site that is not a major source of hazardous air pollutants must change oil and filter every 500 hours or within 1 year plus 30 days of the last change. The air cleaner is inspected every 1,000 hours, and hoses and belts every 500 hours, each also within 1 year plus 30 days.

After any repair that affects reliability, NFPA 110 calls for a run of at least 30 minutes at operating temperature that includes transferring the transfer switches.

How many hours can an emergency generator run under EPA rules?

Federal rules allow unlimited hours in a real emergency. For maintenance checks and readiness testing the limit is 100 hours per calendar year. Up to 50 of those hours may be used for certain non-emergency situations. The limits are in the RICE NESHAP (40 CFR 63.6640(f)) and in the engine performance standards (40 CFR 60.4211(f) for diesel, 60.4243(d) for spark-ignited).

Three points trip owners up:

• Testing must be recommended. The 100 hours cover tests recommended by government, the manufacturer, the vendor, the grid operator or the insurer. NFPA 110 testing fits.
• The 50 hours are not for income. They cannot be used for peak shaving, non-emergency demand response or supplying power under a financial arrangement, apart from narrow local-reliability exceptions. A May 2015 federal appeals court decision vacated the old emergency demand response provisions, and the regulation now shows those paragraphs as reserved.
• Break the limits and the engine stops being “emergency.” It must then meet all requirements for non-emergency engines.

NFPA 110 uses a small part of the 100 hours: twelve 30-minute monthly runs total 6 hours, plus 1.5 hours for a load bank test. Count warm-up and cooldown, because the non-resettable hour meter does. Federal rules require that meter on most emergency engines and a record of why each run happened.

Which codes and air permits apply in Virginia, Maryland and DC?

As of October 2026, fire code editions and air permit rules differ across the three jurisdictions. Check both before you buy or replace a generator.

Item	Virginia	Maryland	DC
Fire code	2021 Statewide Fire Prevention Code	State Fire Prevention Code	2017 DC Fire Code
Model code base	2021 IFC	NFPA 1 and NFPA 101, 2024 eds.	2015 IFC
NFPA 110 edition in model code	2019	Set by the 2024 NFPA codes	2013
Fire AHJ	Local fire official or State Fire Marshal	State Fire Marshal or local fire official	DC Fire and EMS
Air regulator	DEQ	MDE	DOEE

Virginia. The 2021 Virginia codes took effect January 18, 2024, and a 2024 edition is in development. The Statewide Fire Prevention Code requires emergency and standby power systems to be maintained, inspected and tested under load to NFPA 70, NFPA 110 and NFPA 111. Localities that adopt enforcement assign it to a local fire official; elsewhere the State Fire Marshal enforces. For air, 9VAC5-80-1105 exempts emergency engines from minor new source review when each runs no more than 500 hours a year, only for emergencies, maintenance and testing, and the diesel engines in the application total less than 1,675 hp (1,125 kW of generator output). Gasoline engines are exempt below 910 hp (611 kW). Keep records that show the exemption applies. Larger units may need DEQ’s Emergency Generator General Permit or an individual permit. The exemption names diesel and gasoline engines, so confirm natural gas units with DEQ.

Maryland. The State Fire Prevention Code adopts NFPA 1 and NFPA 101, 2024 editions, as amended effective June 23, 2025. It does not apply in Baltimore City except where state law says so. MDE exempts emergency engines under 500 brake horsepower (373 kW) from a permit to construct. Diesel emergency sets from 500 to 2,681 bhp (373 to 2,000 kW) that meet its eligibility terms can use MDE’s general permit to construct; other units use a standard application (MDE permit forms). The general permit applies the federal 100-hour and 50-hour limits, requires five years of records and excludes demand response. Larger sets may also need a Public Service Commission waiver. Confirm any registration duties with MDE.

DC. The 2017 DC Construction Codes took effect May 29, 2020 and are built on the 2015 International Codes. DOEE treats sites with generators as minor sources that generally need a Chapter 2 air permit, and it offers source category permits for diesel and natural gas emergency engines. The diesel permit caps the engine at under 500 hours in any 12 consecutive months for all purposes, applies the federal 100-hour and 50-hour limits, excludes demand response, requires monthly hour totals within 15 days of month end, and requires records for at least three years (five at Title V facilities). Ask DOEE before you install or replace a unit.

What records will the fire marshal ask to see?

NFPA 110 requires records of inspections, tests, exercising and repairs, and your air permit adds run-hour records. A complete file for each generator includes:

• Nameplate data: standby kW, Level, Type, Class, fuel and tank size
• Weekly inspection sheets with date, initials and hour meter
• Monthly run logs with load in kW, duration, readings and time delays
• Transfer switch operations, noting which ATS started each test
• Annual load bank and 36-month reports with interval readings
• Battery and fuel test results, with any remediation
• Breaker and transfer switch maintenance by the electrician
• Every outage run, with reason, start and stop times
• Emergency and non-emergency hours, totaled monthly and yearly
• Deficiencies, corrective actions and the air permit or exemption basis

Federal engine rules and Maryland’s general permit require five years of records; DC’s source category permit requires three (five at Title V sites). Keeping five years covers all three. File it by asset: a QR asset tag on the generator and each transfer switch that opens its history answers an inspector fastest. Our guide to fire and life safety inspection requirements covers how fire marshals review the other systems in the same visit.

Who should do which tasks?

NFPA 110 requires that EPSS components be maintained and tested by qualified persons: people with the skills, knowledge and safety training for that equipment. NFPA’s guidance notes that a trained owner or facility staff member can perform some of these tests.

Task	Typical performer
Weekly inspection, outage logging	Trained facility technician
Monthly run and log	Trained staff or generator technician
Engine service, load bank, 36-month test	Manufacturer-trained technician
ATS maintenance, breakers, IR scan	Licensed electrician
Fuel sampling and polishing	Fuel service specialist
Permits and hour reporting	Owner or manager

In buildings Levaru manages, our technicians handle the routine layer, and we schedule, supervise and document the licensed and manufacturer-trained work as part of a compliance inspection program. Each task closes as a photo-documented work order in the CMMS included with our service, tied to the asset’s QR tag.

For outages longer than any test, see our guide to emergency preparedness for property managers, which covers refueling, generator loads and tenant communication.

What extra rules apply to hospitals and nursing homes?

Medicare rules require hospitals (42 CFR 482.15(e)) and long-term care facilities (42 CFR 483.73(e)) to follow the emergency power inspection, testing and maintenance requirements of NFPA 99, NFPA 110 and the Life Safety Code. CMS surveyors check that generators are inspected weekly, exercised under load for 30 minutes 12 times a year at intervals of 20 to 40 days, and run once every 36 months for 4 continuous hours. They also check 10-second transfer capability and readily available written records.

The Joint Commission surveys the same regime under its own emergency power standard, which excludes the cooldown period from the 30 minutes. A Joint Commission surveyor has noted that some facilities log the monthly run but not the load it carried. For clinical tenants, see our approach to medical office building management.

Frequently asked questions

How often does an emergency generator need to be tested under NFPA 110?

Inspect it weekly and exercise it under load at least monthly for 30 minutes. Diesel units that cannot reach 30 percent of nameplate kW or the manufacturer’s exhaust temperature need an annual supplemental load test. Level 1 systems also need an extended test at least once every 36 months, run for the system’s Class duration but allowed to stop at four hours. Fuel is tested annually and starting batteries monthly.

What is the 30 percent rule for diesel generator testing?

During the monthly exercise, a diesel generator must carry at least 30 percent of its standby nameplate kW, or a load that keeps exhaust gas at the manufacturer’s minimum temperature. The rule targets wet stacking from light loading. If building load is too low, the unit still runs monthly, and an annual load bank test is added: 50 percent for 30 minutes, then 75 percent for an hour.

Does NFPA 110 apply to optional standby generators?

No. The 2025 edition states that it does not cover optional standby systems, which serve loads where life safety does not depend on the generator. Those systems still fall under the electrical code, federal air rules and the manufacturer’s maintenance schedule, and an insurer or lease may require testing. A generator that feeds both optional and life-safety loads is treated as an emergency power supply system and maintained to NFPA 110.

Can a real power outage count as the monthly generator test?

Yes, if you record it. NFPA 110 and Virginia’s fire code allow recorded standby use to substitute for a scheduled test, provided you keep the same record a test would produce: date, duration, load, readings and any problems. Emergency runs also do not count against the federal 100-hour limit, though you must log them as emergency hours from the non-resettable hour meter.

How many hours a year can an emergency generator run for testing?

Under federal EPA engine rules, up to 100 hours per calendar year for maintenance checks and readiness testing, and unlimited hours in a real emergency. Up to 50 of those 100 hours may cover certain non-emergency uses, but not peak shaving or paid demand response. State and DC permits can add limits, such as DC’s source category cap of under 500 total hours in any 12 months.

What belongs on a generator maintenance checklist?

Weekly: alarms, leaks, fluid and fuel levels, block heater, battery charger, transfer switch status and the hour meter. Monthly: a logged load run with kW and readings, transfer switch operation and battery tests. Annually: fuel testing, full engine service, breaker exercise, transfer switch maintenance by a licensed electrician, and a load bank test if monthly runs were light. Add the manufacturer’s tasks and your air permit’s record-keeping.

Do I need an air permit for an emergency generator in Maryland, Virginia or DC?

It depends on size. Maryland exempts emergency engines under 500 brake horsepower from a permit to construct. Virginia exempts emergency engines that run no more than 500 hours a year when the aggregate diesel rating stays under 1,675 hp. DOEE generally requires a permit in DC and offers source category permits for emergency engines. Federal hour limits and record-keeping apply in all three.