Why a Structured Maintenance Schedule Matters
Emergency generators sit idle for the vast majority of their operational life. When utility power fails, that idle machine must start and pick up load quickly -- within 10 seconds for a Type 10 system serving emergency or healthcare loads -- and then carry the load for as long as the outage lasts. The only way to ensure that level of reliability is through disciplined, scheduled preventive maintenance.
NFPA 110, the Standard for Emergency and Standby Power Systems, does not merely suggest maintenance. Chapter 8 requires a routine maintenance and operational testing program, including weekly inspection, monthly exercise under load, and specific requirements for starting batteries, fuel quality, circuit breakers, and records. Engine-specific tasks such as oil, filter, and coolant service come from the manufacturer's recommendations. The Authority Having Jurisdiction (AHJ) will verify compliance during inspections, and incomplete records are a common finding.
This guide provides an interval-based maintenance schedule for diesel-powered emergency generators that combines NFPA 110 requirements, EPA recordkeeping obligations, and common industry practice. Where a task is required by NFPA 110, the table shows the section; where it comes from manufacturer guidance or practice, the table says so. Section numbers are from the 2016 through 2025 editions unless noted (the 2010 edition, which CMS enforces for healthcare, numbers the battery and fuel sections 8.3.7 and 8.3.8). Adapt the tasks to your manufacturer's recommendations and your AHJ's adopted edition.
Weekly Maintenance Tasks
Weekly inspections are brief, visual checks designed to catch developing problems before they become failures. NFPA 110 Section 8.4.1 requires the EPSS, including transfer switches and other appurtenant components, to be inspected weekly. Level 1 starting batteries must also be inspected weekly (Section 8.3.6).
| Task | Description | NFPA 110 Reference | Time Estimate |
|---|---|---|---|
| Visual walk-around | Inspect for fluid leaks (fuel, oil, coolant), physical damage, pest intrusion, and unusual conditions | 8.4.1 | 5 min |
| Check engine heater | Verify the engine jacket water heater is energized and holding the temperature the manufacturer specifies for cold start and load acceptance | 8.4.1; 5.3.1 | 2 min |
| Battery and charger status | Confirm the battery charger is operating and displaying a float charge; check battery condition, connections, and (where accessible) electrolyte levels. Note any fault indicators | 8.3.6 (weekly for Level 1) | 5 min |
| Control panel indicators | Check for active alarms, fault codes, or warning lights on the generator control panel; confirm the control switch is in automatic | 8.4.1 | 2 min |
| Transfer switch | Check the ATS controller for alarms and confirm it is in automatic mode | 8.4.1 | 2 min |
| Enclosure/room condition | Verify louvers are unobstructed, room is clean, no storage items blocking airflow or access | 8.4.1 | 3 min |
| Security verification | Confirm access doors are secure, emergency shutdown signage is visible, and fire extinguisher is in place | Practice | 2 min |
| Hour meter reading | Record the current non-resettable hour meter reading in the operations log | Practice; EPA (see Documentation) | 1 min |
Engine Heater Temperature
NFPA 110 requires the generator to be heated as needed to keep the water jacket and battery at the temperature the manufacturer specifies for cold start and load acceptance. Use your manufacturer's value, not a generic number. The 2019 edition sets the low coolant temperature alarm at 20 degrees F (11 degrees C) below that regulated temperature, so a low-temperature alarm usually means a heater or thermostat problem that needs attention before the next start.
Monthly Maintenance Tasks
Monthly maintenance includes the most important single activity in your generator program: a loaded exercise test. NFPA 110 Section 8.4.2 requires monthly exercise under load.
| Task | Description | NFPA 110 Reference | Time Estimate |
|---|---|---|---|
| Exercise under load | Run the generator for a minimum of 30 minutes. Diesel units must carry at least 30% of nameplate kW or a load that maintains the manufacturer's minimum exhaust gas temperature. Healthcare facilities must test 12 times a year at intervals of 20 to 40 days | 8.4.2 | 45 min |
| Transfer switch operation | Electrically operate each automatic transfer switch (ATS) from the normal position to the emergency position and back | 8.4.6 | Included in exercise |
| Battery testing | Maintainable (flooded) batteries: test and record electrolyte specific gravity, or use an approved alternative method. Non-maintainable batteries (2025 edition): test by conductance, ohmic, carbon pile, or cranking voltage drop methods | 8.3.6 | 15 min |
| Engine oil level | Check oil level on the dipstick with the engine off and level. Top off if below the full mark | Manufacturer | 5 min |
| Coolant level | Inspect coolant level in the expansion tank or radiator (engine cool). Top off with correct coolant mixture if low | Manufacturer | 5 min |
| Fuel level | Verify the day tank and main fuel storage tank levels. Confirm fuel supply valve positions are correct | Manufacturer; see Class requirements | 5 min |
| Belt inspection | Inspect drive belts for cracking, glazing, fraying, or improper tension. Check belt alignment | Manufacturer | 5 min |
| Hose inspection | Examine coolant hoses and fuel lines for softness, bulging, cracking, or evidence of leaks | Manufacturer | 5 min |
| Air intake inspection | Check the air filter restriction indicator if equipped. Verify the air intake is unobstructed | Manufacturer | 3 min |
| Record operational data | Log oil pressure, coolant temperature, battery voltage, output voltage, frequency, and load during the exercise test | 8.4.2 | Included in exercise |
Monthly Exercise Testing: Getting It Right
The monthly exercise test is more than a checkbox item. It serves multiple purposes:
- Reduces wet stacking: Running under adequate load helps prevent the buildup of unburned fuel that occurs during extended no-load or light-load operation
- Exercises the fuel system: Cycles fuel through injectors, pumps, and filters
- Tests the ATS: Verifies the complete transfer switch sequence functions correctly
- Generates baseline data: Monthly operating parameter records reveal gradual changes that indicate developing problems
Important
If a diesel generator's monthly tests do not reach 30% of nameplate kW or the manufacturer's minimum exhaust gas temperature, NFPA 110 (Section 8.4.2.3 in the 2010 edition) still requires monthly exercise with the available load, plus an annual test with supplemental load: at least 50% of nameplate for 30 minutes, then at least 75% for 60 minutes, for 1.5 continuous hours. Extended light-load operation causes wet stacking in diesel engines, which degrades performance over time.
Quarterly Maintenance Tasks
Quarterly tasks focus on systems that degrade slowly and require less frequent attention but are critical to reliable operation. These intervals come from common practice and manufacturer guidance, not NFPA 110; follow your manufacturer's schedule where it differs.
| Task | Description | NFPA 110 Reference | Time Estimate |
|---|---|---|---|
| Coolant concentration test | Test coolant for freeze point protection, pH, and supplemental coolant additive (SCA) concentration using test strips or a refractometer. Correct as needed | Manufacturer | 15 min |
| Battery connections | Clean battery terminals and cable connections. Check for corrosion, tighten to manufacturer torque specifications, and apply anti-corrosion treatment | Manufacturer; 8.3.6 | 15 min |
| Exhaust system inspection | Inspect the entire exhaust system from the engine manifold to the discharge point for leaks, corrosion, loose clamps, and damaged insulation or rain caps | Manufacturer | 20 min |
| Fuel system inspection | Inspect fuel lines, fittings, day tank float switches, and fuel transfer pumps for leaks or deterioration | Manufacturer | 15 min |
| Verify emergency stops | Test all remote and local emergency stop buttons to confirm they shut down the engine | Manufacturer | 10 min |
| Inspect vibration isolators | Check engine and alternator mounting pads and vibration isolators for deterioration or excessive compression | Manufacturer | 10 min |
Battery Testing Detail
Starting batteries are a frequent cause of failure to start, which is why NFPA 110 Section 8.3.6 sets specific requirements:
- Level 1 starting and control batteries must be inspected weekly (the 2025 edition allows monthly inspection for Level 2) and maintained in full compliance with the manufacturer's recommendations, including electrolyte levels and battery voltage
- Maintainable (flooded) batteries must be tested monthly with a record of electrolyte specific gravity; the alternative test methods listed for non-maintainable batteries are permitted in its place where applicable
- Under the 2025 edition, non-maintainable batteries (no electrolyte access) must be tested monthly by conductance, ohmic, carbon pile load, or cranking voltage drop testing
- Defective batteries must be replaced immediately upon discovery of defects
- Confirm charger output voltage matches the battery manufacturer's requirements
Replace batteries on the schedule your battery and generator manufacturers recommend, and sooner if testing shows declining performance.
Semi-Annual Maintenance Tasks
Semi-annual maintenance addresses consumables and components with moderate service intervals. Many manufacturers set these intervals by calendar time or operating hours, whichever comes first, so check your engine's maintenance manual.
| Task | Description | NFPA 110 Reference | Time Estimate |
|---|---|---|---|
| Change engine oil and filters | Drain engine oil and replace the oil filter(s). Refill with manufacturer-specified oil grade and quantity. Take an oil sample if you trend oil condition | Manufacturer | 45 min |
| Replace fuel filters | Replace primary and secondary fuel filters. Bleed the fuel system per manufacturer procedure. Check for water contamination | Manufacturer | 30 min |
| Clean or replace air filter | Remove and inspect the air filter element. Replace if dirty or at the manufacturer-specified interval, whichever comes first | Manufacturer | 15 min |
| Inspect starter motor | Check the starter motor for proper engagement, unusual noise, and secure mounting. Inspect wiring connections | Manufacturer | 15 min |
| Check governor and voltage regulator | Verify frequency stability and voltage regulation are within the manufacturer's specifications during loaded operation | Manufacturer | Included in exercise |
| Inspect fuel tank integrity | Check main fuel storage tank for water accumulation, corrosion, and structural integrity. Drain water from the tank sump | Manufacturer; SPCC where applicable | 20 min |
Oil Analysis Program
Sending oil samples to a laboratory for analysis at each oil change can give early warning of internal engine wear, coolant contamination, fuel dilution, and other developing problems. Label each sample with the unit identifier, hour meter reading, and oil hours so results can be trended over time.
Annual Maintenance Tasks
Annual maintenance includes the most comprehensive inspections, the annual fuel quality test, and -- if your monthly tests do not reach the minimum load -- the supplemental load test required by NFPA 110.
| Task | Description | NFPA 110 Reference | Time Estimate |
|---|---|---|---|
| Supplemental load test (if required) | Required only if monthly tests do not reach 30% of nameplate or the manufacturer's minimum exhaust temperature: at least 50% of nameplate kW for 30 minutes, then at least 75% for 60 minutes (1.5 continuous hours), usually with a load bank. Record readings at regular intervals | 8.4.2.3 (2010 edition) | 2-3 hours |
| Fuel quality test | Test fuel at least annually using appropriate ASTM standards or the manufacturer's recommendations. Polish or replace fuel as the results indicate | 8.3.7 | 1 hour plus lab time |
| Circuit breaker exercise | Exercise EPSS circuit breakers annually with the generator off (Level 1, 600 volts or less); breakers over 600 volts are exercised every six months and tested under simulated overload every two years | 8.4.7 | 1 hour |
| Coolant system service | Service or replace coolant and replace the thermostat at the intervals the engine manufacturer specifies | Manufacturer | 2 hours |
| Comprehensive ATS service | Inspect ATS contacts for pitting and wear, test all sensing and timing functions, verify bypass isolation capability, and exercise the manual transfer mechanism | Manufacturer; NFPA 70B where adopted | 2 hours |
| Inspect and clean alternator | Inspect alternator windings for contamination, check bearing condition, test insulation resistance against the manufacturer's acceptance value, and clean as needed | Manufacturer | 1 hour |
| Inspect and test all sensors | Verify calibration and operation of oil pressure, coolant temperature, coolant level, and other engine protection sensors | Manufacturer | 1 hour |
| Tighten all electrical connections | Check torque on all power connections at the generator, ATS, and distribution panel; NFPA 70B also calls for infrared thermography at least every 12 months | Manufacturer; NFPA 70B where adopted | 1 hour |
| Inspect enclosure and ventilation | Check weatherproofing, door seals, louver operation, cooling airflow path, and exhaust discharge condition | Manufacturer | 30 min |
| Review compliance documentation | Audit the maintenance log, operating log, and test records for completeness. Verify EPA hour tracking. Confirm your next 36-month test date (Level 1). Prepare for AHJ inspection | 8.4; EPA | 1 hour |
Annual Supplemental Load Test Protocol
When monthly exercises do not reach the minimum load, the annual supplemental test is how you meet NFPA 110 and burn off the effects of light-load running. Level 1 systems also need a 4-hour test at least once every 36 months (Section 8.4.9), which can be combined with the annual supplemental test: the first 3 hours at not less than 30% of nameplate (or the minimum exhaust temperature) and the final hour at not less than 75%. See our 36-month 4-hour load test guide.
Pre-test checklist:
- Verify oil and coolant levels are correct
- Confirm fuel supply is adequate for the test duration plus reserve
- Ensure the load bank is properly connected and rated for the planned load steps
- Brief all personnel on safety procedures and emergency shutdown locations
During the test, record the following at regular intervals (for example, every 15 minutes):
| Parameter | Acceptable Range |
|---|---|
| Output voltage (each phase) | Within the manufacturer's regulation tolerance |
| Output frequency | Within the manufacturer's tolerance for rated frequency |
| Engine oil pressure | Manufacturer specification |
| Coolant temperature | Manufacturer's normal operating range |
| Exhaust temperature | Per manufacturer specification |
| Load (kW) | At least 50% of nameplate for 30 minutes, then at least 75% for 60 minutes |
| Battery charging voltage | Per charger and battery manufacturer |
Safety Warning
Load bank testing involves high-voltage electrical connections and extreme heat from the load bank resistive elements. Only qualified personnel should perform load bank connections. Maintain all required clearances from the load bank during operation and ensure adequate ventilation to dissipate heat.
Documentation and Logging Requirements
NFPA 110 requires records of inspections, tests, and maintenance, including the date, the servicing personnel, and any unsatisfactory condition with the corrective action taken. In healthcare, CMS surveyors look for written records of maintenance and testing that are maintained and readily available. Your documentation program should include the following elements; a printable NFPA 110 test log can help standardize them.
Operations Log
Maintain a chronological log of every generator start, whether planned or unplanned:
| Field | Description |
|---|---|
| Date and time | Start and stop time of each operating period |
| Hour meter reading | Reading at start and stop |
| Reason for operation | Emergency, scheduled test, maintenance, demand response, or other |
| Load carried | Approximate kW or percentage of rated load |
| Operating parameters | Voltage, frequency, oil pressure, coolant temperature at steady state |
| Operator initials | Person responsible for the operating period |
| Anomalies noted | Any unusual conditions observed during operation |
Maintenance Log
Document every maintenance activity performed:
| Field | Description |
|---|---|
| Date | Date the maintenance was performed |
| Hour meter reading | Current reading at time of service |
| Task performed | Specific description of the work completed |
| Parts replaced | Part numbers and quantities of any replaced components |
| Fluid quantities | Oil, coolant, or fuel quantities added or replaced |
| Technician | Name and company of the person performing the work |
| Next scheduled service | Date or hour meter reading for the next required service |
Record Retention
- NFPA 110 and accreditors -- Confirm the retention period your AHJ and accreditor expect. At minimum, keep enough history to show your most recent 36-month test (Level 1) and every monthly test since your last inspection or survey
- EPA RICE NESHAP -- For engines subject to 40 CFR Part 63, Subpart ZZZZ, records must be kept for five years after each occurrence. Owners of emergency engines must also record hours of operation from a non-resettable hour meter, separating emergency and non-emergency hours; maintenance and readiness testing is limited to 100 hours per calendar year
- State and local permits may specify additional retention requirements
- Store records in a format that is readily accessible for AHJ inspections
Integrating the Schedule Into Your Facility Program
A maintenance schedule is only effective if it is consistently executed and documented. The following strategies help ensure compliance:
Use a CMMS or work order system. Enter all scheduled tasks as recurring work orders with appropriate frequencies. Assign responsible personnel and set up automated notifications for upcoming and overdue tasks.
Establish a dedicated generator log. Whether physical or digital, maintain a single comprehensive log at or near the generator that captures all inspections, tests, and maintenance activities. AHJ inspectors expect to find this log readily available.
Train multiple staff members. Ensure at least two facility staff members are trained and authorized to perform weekly and monthly inspections and exercise tests. Reliance on a single individual creates risk when that person is unavailable.
Contract what you cannot perform in-house. Semi-annual and annual tasks often require specialized tools, training, and test equipment. Establish a service contract with a qualified generator service provider for these intervals.
Schedule annual maintenance before your AHJ inspection. If your fire marshal or other AHJ conducts annual inspections on a predictable schedule, complete your annual generator maintenance well before the inspection so that records are current and any deficiencies identified during maintenance can be corrected first.
Summary Maintenance Calendar
The following summary provides a quick-reference view of all maintenance intervals:
| Interval | Key Tasks | Typical Duration |
|---|---|---|
| Weekly | Visual inspection (NFPA 110), engine heater, battery and charger (weekly for Level 1), control panel and ATS check | 15-20 minutes |
| Monthly | Loaded exercise test (30+ min), ATS transfer test, battery testing, fluid levels, belt/hose inspection | 60-90 minutes |
| Quarterly | Coolant test, battery connections, exhaust inspection, emergency stop test | 60-90 minutes |
| Semi-Annual | Oil and filter change, fuel filter change, air filter service, fuel tank check (or per manufacturer hours) | 2-3 hours |
| Annual | Fuel quality test, circuit breaker exercise, supplemental load test if monthly loading falls short, ATS comprehensive service, alternator inspection | 8-12 hours (may span multiple days) |
| Every 36 months | 4-hour load test for Level 1 systems | 4+ hours |
Consistent execution of this maintenance schedule, adjusted to your manufacturer's recommendations and your AHJ's adopted edition, supports NFPA 110 compliance and EPA recordkeeping, and most importantly helps ensure your emergency generator will perform when your facility depends on it. The cost of preventive maintenance is a fraction of the cost of a generator that fails to start during a critical power outage.
Sources and References
- NFPA 110: Standard for Emergency and Standby Power Systems -- National Fire Protection Association. https://www.nfpa.org/codes-and-standards/nfpa-110-standard-development/110
- NFPA 110 Maintenance and Testing -- Curtis Power Solutions. https://www.curtispowersolutions.com/nfpa-110-maintenance-testing
- NFPA 110 for Emergency Power Systems: 2025 Updates (PowerHour, August 21, 2025) -- Cummins Inc. https://www.cummins.com/sites/default/files/2026-04/2025-aug-nfpa-110-for-emergency-power-systems.pdf
- NFPA 110 Levels 1 and 2 Standards for Generator Systems (Information Sheet 25) -- Clifford Power Systems. https://cliffordpower.com/wp-content/uploads/2024/02/IS_25_NFPA110_Level1_2-REV-11-1-19.pdf
- Complying with Inspection, Testing and Maintenance for Electrical Systems -- Health Facilities Management (HFM) Magazine. https://www.hfmmagazine.com/articles/4461-complying-with-inspection-testing-and-maintenance-for-electrical-systems
- Form CMS-2786R, Fire Safety Survey Report, 2012 Life Safety Code, Health Care (K918) -- Centers for Medicare and Medicaid Services. https://www.cms.gov/Medicare/CMS-Forms/CMS-Forms/downloads/cms2786R.pdf
- Diesel Generator Maintenance: Feasibility and Benefits of No-Load Exercising (Power Systems Topics 130) -- Kohler Co. https://resources.kohler.com/power/kohler/industrial/pdf/NoLoadMaintenanceWP.pdf
- 40 CFR 63.6640 -- Emergency stationary RICE operating limits -- Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/cfr/text/40/63.6640
- 40 CFR 63.6655 -- Records for stationary RICE -- Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/cfr/text/40/63.6655
- 40 CFR 63.6660 -- Record retention for stationary RICE -- Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/cfr/text/40/63.6660
- 40 CFR Part 63, Subpart ZZZZ -- EPA RICE NESHAP for Stationary Reciprocating Internal Combustion Engines. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-63/subpart-ZZZZ
- NFPA 70B: Standard for Electrical Equipment Maintenance -- National Fire Protection Association. https://www.nfpa.org/codes-and-standards/nfpa-70b-standard-development/70b
- ASTM D975: Standard Specification for Diesel Fuel -- ASTM International. https://store.astm.org/d0975-26b.html
- NFPA 70E: Standard for Electrical Safety in the Workplace -- National Fire Protection Association. https://www.nfpa.org/codes-and-standards/nfpa-70e-standard-development/70e
