Best Practices for Testing and Commissioning Industrial Generator Systems

A newly installed or freshly overhauled industrial generator is not a reliable asset the moment it lands on your pad. It becomes one only after a disciplined program of testing and commissioning proves, on paper and under load, that the engine, alternator, fuel system, controls, transfer switches, and protection settings all behave exactly as specified when the utility drops.

Skipping or shortcutting that program is how facilities end up with a $250,000 generator that starts, runs, and then trips offline the first time it sees a real step load during a hurricane. It is also how hospitals lose accreditation, data centers lose tenants, and plant managers lose jobs.

This guide is for facility engineers, contractors, consulting specifiers, and the operations teams who have extensive experience with the system. We will walk through the full testing and commissioning lifecycle for industrial diesel and natural gas generator sets, from Factory Acceptance Test through Site Acceptance Test, load bank verification, NFPA 110 compliance testing, and the documentation handover that closes the project out.

Why Testing and Commissioning Matter More Than the Generator Itself

Industry studies on equipment commissioning consistently show that defects caught at the factory cost roughly an order of magnitude less to fix than the same defects caught after site installation, and another order of magnitude less than those discovered during an actual emergency. A loose fuel line identified on a test stand is a ten-minute repair; the same loose line found during a utility outage at 3 a.m. is a critical-load event.

Beyond economics, three forces make rigorous commissioning non-negotiable for most commercial and industrial installations:

1. Code and accreditation compliance. NFPA 110 (Standard for Emergency and Standby Power Systems), NFPA 99 (Health Care Facilities Code), NFPA 37 (Stationary Combustion Engines), and the Joint Commission environment-of-care standards all require documented acceptance testing, ongoing operational testing, and retrievable records. An Authority Having Jurisdiction (AHJ) inspection that can’t find the records is effectively the same as never having tested.
2. Warranty activation. For most manufacturers, including Caterpillar, Cummins, Kohler, MTU, Generac, and John Deere, the warranty clock starts at commissioning, not at delivery. An improperly commissioned unit can void coverage entirely.
3. Insurance and business continuity. Many property and business-interruption carriers now require proof of annual load bank testing and a documented maintenance schedule as a condition of coverage for critical facilities.

In short: the generator is the asset. Commissioning is what converts it from a large metal object into a reliable power system.

The Commissioning Lifecycle: Five Phases

Industrial generator commissioning follows the same five-phase pattern used for any major capital equipment, scoped specifically to rotating electrical machinery and emergency power systems.

Phase	What Happens	Where	Who Owns It
1. Factory Acceptance Test (FAT)	Verify the generator performs to specification before shipment	Manufacturer’s test cell or supplier’s yard	Supplier and purchaser’s witness
2. Pre-Installation and Receiving	Inspect on arrival, verify no transit damage, confirm scope	Job site	Contractor and owner
3. Pre-Commissioning Checks	Mechanical, electrical, and fluid verification before first start	Job site	Installation contractor
4. Site Acceptance Test (SAT) and Load Bank	First start, functional testing, load testing, protection testing	Job site	Commissioning engineer and AHJ for EPSS
5. Handover and Documentation	Burn-in period, final reports, training, maintenance plan launch	Job site	Owner takes possession

Each phase gates the next. Deficiencies are tracked on a punch list categorized as Type-A (must be cleared before proceeding), Type-B (must be cleared before handover), or Type-C (cosmetic, tracked but not blocking). Moving forward with open Type-A items is the single most common way commissioning goes wrong.

Phase 1: Factory Acceptance Test (FAT)

The FAT is the last controlled environment in which to catch defects before they travel to the job site at the end of a truck or ocean container. A proper FAT for a generator set covers:

• Visual and dimensional inspection against the purchase order and approved submittal drawings, including the frame, skid, subbase tank, enclosure, control panel model, alternator rating, and nameplate data.
• No-load start test to confirm the engine cranks, builds oil pressure, reaches rated speed, and stabilizes voltage and frequency.
• Load bank test at rated capacity. Typical sequence: 25% for 30 minutes, 50% for 30 minutes, 75% for 30 minutes, 100% for at least 60 minutes, and where applicable 110% for 10 minutes. Parameters recorded every 5 to 15 minutes include kW, kVA, power factor, voltage (all phases), frequency, coolant temperature, oil pressure, exhaust gas temperature, fuel pressure, and ambient temperature. This is the heart of the FAT; see our load bank testing guide for the full procedure.
• Step load acceptance test per ISO 8528-5, verifying the generator can accept its specified block loads within the allowed voltage and frequency dip and recovery windows.
• Alarm and shutdown verification for low oil pressure, high coolant temp, overspeed, overcrank, emergency stop, low fuel level, high fuel level, battery charger fault, and any site-specific alarms.
• Controls and communications. Verify the genset controller (for example, Cummins PowerCommand, Caterpillar EMCP, DSE, ComAp) displays correct values and that Modbus, BACnet, or other BMS protocols communicate with simulated upstream devices.
• Insulation resistance (megger) test on the alternator windings, with readings corrected to a standard temperature.

For buyers purchasing new or surplus units from a reseller, FAT practice varies. A reputable power-generation dealer, and this is part of what Depco’s 30,000-square-foot Houston yard is built around, will run the equivalent of a FAT in-yard before shipment, including a load bank test and a written test report. Always ask for a copy of the test sheet with the unit’s serial number on it. If a dealer cannot produce one, treat the unit as untested and budget accordingly.

Witnessing the FAT

For critical installations like data centers, hospitals, and oil and gas facilities, the owner’s representative or commissioning agent (CxA) should physically witness the FAT. Remote witnessing via video is acceptable for smaller projects but should be a documented video with test data overlays, not a live stream that evaporates at the end of the call.

Phase 2: Pre-Installation and Receiving Inspection

The generator arrives on site. Before the rigging crew drives off, and before the equipment gets bolted down, complete these checks:

• Photograph the unit on the trailer from every angle. Transit damage claims are won and lost on timestamps and photos.
• Verify the nameplate matches the purchase order: kW rating, voltage, phase, Hz, standby vs. prime rating, alternator model, engine serial number. (See our generator power ratings guide for what each rating means.)
• Check fluid levels (coolant, oil, fuel) and confirm that shipping-plug blanks on the exhaust, air intake, and crankcase breather have not been left in place.
• Inspect for physical damage to the radiator fins, alternator terminal box, control panel door, enclosure panels, and fuel tank.
• Confirm accessories. The battery, battery charger, jacket water heater, louvers, silencer, flexible exhaust connector, and remote annunciator ordered with the unit are all present.

Any deficiencies go on the punch list immediately, before the freight carrier is released.

Phase 3: Pre-Commissioning Checks

Pre-commissioning is the point at which the generator is installed, connected, and fueled, but has not yet been started for the first time on site. This is the highest-risk moment in the entire project. A single wrong wire, a forgotten shipping plug, or a mis-torqued fuel fitting can destroy an engine on its first start.

Mechanical verification

• Vibration isolators are installed correctly, shimmed level, and shipping blocks are removed
• Exhaust piping is complete, supported, and has a proper flexible connector at the engine manifold; long-radius elbows are used where applicable; muffler and rain cap are correctly sized and placed
• Air intake path is unobstructed, air cleaner and clamps inspected, and louvers operate
• Fuel piping is pressure-tested, leak-checked, and primed; day-tank level controls, transfer pump, and base-tank components are verified; fuel system is bled before first start
• Coolant is filled to the manufacturer’s specification in both HT and LT circuits; antifreeze concentration, DCA concentration, and freeze point are recorded
• Lube oil is at the full mark on the dipstick, quality verified, and filtration system inspected
• All shipping plugs, stops, and tags are removed
• Belt tensions, hose clamps, and all fluid connections are verified leak-free
• Rotating components are free of debris and have adequate clearance for service access

Electrical verification

• Insulation resistance of alternator windings is re-measured and compared to the FAT reading
• All power cables are landed, torqued to specification, and labeled; neutral connection is verified correct for the system grounding configuration
• Phase rotation is confirmed with a rotation meter. This is critical, because reversed rotation can destroy motor-driven loads.
• Ground conductors and ground rods are installed and continuity-tested
• Control wiring between the generator, ATS, remote annunciator, and BMS is landed and rung out point-to-point
• Battery is fully charged; DC wiring to battery and starter terminals verified; charger AC connection and float voltage are correct
• Jacket water heater and any oil-sump heater are energized and the block is at manufacturer-recommended temperature (typically 90 to 120°F) before first start
• Alternator and control panel heaters are wired and functional
• Block heater and battery charger circuits have reliable power

Safety verification

• Emergency stop buttons (local at the genset, remote at the control room, and any required in the generator room exit) are wired, tested for continuity, and clearly labeled
• Fire suppression and detection systems in the generator room are operational
• Ventilation louvers, fans, and dampers operate correctly
• Signage and warning notices are posted
• Fuel spill containment is in place
• “Do Not Use” tags are placed on starter switches during any maintenance work
• All guards and covers are secured; access is restricted to authorized personnel

Only after every item on the pre-commissioning checklist is signed off does the unit move to first start.

Phase 4: Site Acceptance Test (SAT) and Load Testing

The SAT proves that the generator, the transfer switches, the distribution equipment, and the loads all work together as a system, in the real environment, under real loads. It is the most visible and most scrutinized part of the commissioning program.

Step 4.1. Pre-Start and First Engine Start

Before cranking the engine, run the pre-lube cycle for at least 60 seconds to fill the main oil gallery. Confirm main oil pressure reaches the manufacturer’s minimum (typically 30 kPa / 4.4 psi or higher) and holds for the full pre-lube duration. Verify the ECM is energized, the fuel priming cycle is complete, and no ECM alarms or faults are active.

Start the engine locally, at the genset control panel, in manual mode. Do not connect load yet. Verify and record:

• Oil pressure builds within the manufacturer’s specification within a few seconds
• Engine reaches rated speed (1800 rpm for 60 Hz, 1500 rpm for 50 Hz) smoothly with no hunting
• Alternator voltage stabilizes at the set point on all three phases (line-to-line and line-to-neutral)
• Frequency stabilizes at 60.0 Hz (or 50.0 Hz) with no measurable drift
• Fuel pressure, coolant temperature, exhaust operation, rain cap movement, battery charge rate
• No abnormal noises, vibration, or visible smoke beyond a brief initial puff
• No leaks develop; walk around the unit with a flashlight
• No ECM alarms or fault codes

Let the unit run for 10 to 15 minutes at no load, then shut down normally and inspect. Check for leaks, verify fault codes, and confirm control settings return to standby mode.

Step 4.2. Protection and Alarm Testing

With the unit off or in a known state, simulate each alarm and shutdown condition and verify the correct response:

• Emergency stop (local, remote, and any fire-alarm-initiated stops)
• Low oil pressure
• High coolant temperature
• Overspeed
• Overcrank. Disable fuel injection, attempt start, and confirm the controller locks out after three crank cycles (10 seconds cranking, 10 seconds rest).
• Low fuel
• Battery failure or charger failure
• Transfer switch failure

Verify that alarms annunciate locally, at the remote annunciator, and at the building management system. For NFPA 110 Level 1 installations, the remote annunciator is required.

Step 4.3. Automatic Transfer Switch (ATS) Testing

The generator is only half of the emergency power system. The ATS, and the full signal chain from utility loss detection through engine start through load transfer, has to work flawlessly. For background on how ATS equipment fits into the broader power distribution architecture, see our ATS vs. switchgear comparison and our explainer on how transfer switches work.

Best practice:

• Initiate all transfer tests from the ATS test switch, not the generator control panel. Starting from the ATS tests the entire signal chain from loss-of-power detection forward, which is what actually happens during a utility event.
• Verify the engine start signal is generated as soon as the programmed utility loss time delay expires
• Verify transfer occurs only after the generator has reached rated voltage and frequency (typically ~90% voltage, ~95% frequency)
• For NFPA 110 Type 10 installations, the entire sequence from utility loss to load transfer must complete within 10 seconds
• Verify all control wiring terminations: remote start, load controls, voltage and current ratings for normal and emergency power connections, cabinet seal
• Simulate utility return and verify the time-delay-return-to-normal and engine cool-down sequences operate correctly

Step 4.4. Load Bank Testing

The load bank test is the heart of site acceptance. It verifies that the generator can actually deliver its nameplate output in the real installation, with the real cooling air path, the real exhaust back-pressure, and the real ambient conditions.

A standard acceptance load profile looks like this:

Step	Load	Duration	Purpose
1	25%	30 min	Warm-up, initial data capture
2	50%	30 min	Mid-range stability
3	75%	30 min	Cooling system verification
4	100%	60 to 120 min	Full capacity, heat soak, NFPA 110 acceptance
5	Step load	Per ISO 8528-5	Voltage and frequency dip and recovery
6	Cooldown at 25 to 30%	10 to 15 min	Preventing thermal shock

Why resistive (not just reactive) load banks matter. A resistive load bank loads the engine. A reactive load bank loads the alternator. For true capacity verification, and for any installation with motor loads, VFDs, or UPS inputs, the acceptance test should include both unity power factor and 0.8 lagging power factor loading if the service will see that profile. See our power factor guide for more on why this matters for sizing and testing.

Why this catches real problems. A wet-stacked engine running at 30% for years will look fine on a weekly exercise but smoke heavily at 75% and fail at 100%. Undersized cooling air paths, clogged radiator cores, restricted exhaust systems, and marginal fuel delivery all reveal themselves in the last 30 minutes of a 2-hour full-load run, not in the first 30 seconds.

For a deeper walkthrough of the load bank procedure, step loads, and what to record, see our complete generator load bank testing guide.

Step 4.5. NFPA 110 Acceptance Testing (Emergency Power Supply Systems)

For any installation classified as an Emergency Power Supply System (EPSS) under NFPA 110 (hospitals, high-rises, many commercial buildings, most data centers, life-safety applications), there is an explicit on-site acceptance test required before the AHJ will sign off. The test protocol in NFPA 110 Chapter 7 requires, at minimum:

• A cold start: the engine must start and accept full rated load without any pre-warming period or idle time
• A 2-hour continuous load test with the AHJ present
• Demonstration of the full EPSS (generator, transfer switches, distribution equipment, and controls) carrying all emergency loads that will be connected in service
• For Type 10 systems (healthcare), restoration of power to critical loads within 10 seconds of a utility failure

Requirements are updated periodically and exact paragraph citations vary by edition. Always confirm the current edition adopted by your local AHJ. Some jurisdictions are still on NFPA 110-2010 while others have adopted 2016, 2019, 2022, or 2025. Your AHJ’s adopted edition is the one that governs your project.

NFPA 110 also requires that the manufacturer’s maintenance and testing recommendations be followed unless the AHJ specifies otherwise, and that written test procedures and records be retained and available for inspection.

Phase 5: Handover and Documentation

A generator that is tested but undocumented is a generator that hasn’t been tested. Handover closes the commissioning project and starts the asset’s operational life.

Required Documentation Package

At a minimum, the owner should receive:

• Signed FAT report with test data sheets
• Signed SAT report with test data sheets
• Load bank test report with recorded parameters at each load step
• NFPA 110 acceptance test report signed by the AHJ (for EPSS installations)
• As-built one-line diagrams and control schematics (red-lined from the original design if field changes were made)
• Alarm and protection set-point report with all values as installed
• Manufacturer’s O&M manuals (NFPA 110 requires at least two sets for EPSS)
• Spare parts list with recommended stocking quantities
• Training attendance sign-in sheet
• Warranty registration confirmation
• Written maintenance and testing schedule derived from manufacturer recommendations and NFPA 110 Annex A where applicable

Operator and Maintenance Training

Schedule training for operations staff and the facility maintenance team covering:

• Normal start and stop procedures (local and remote)
• Reading and interpreting the controller display
• Emergency stop procedure and restart
• Reading the annunciator
• Monthly and weekly inspection procedures
• Fuel, oil, coolant, and battery checks
• What to do (and not do) during an actual utility event

For a practical maintenance framework to hand to the operations team at this stage, our generator maintenance guide provides a starting point.

Ongoing Testing Schedule

The commissioning program doesn’t end at handover. It transitions into an ongoing operational testing program. For NFPA 110 EPSS installations, recent editions of NFPA 110 Chapter 8 require, generally:

• Weekly inspection of the EPSS, including fuel, oil, coolant, and battery levels; control panel indications; and ambient conditions. Inspection does not require running the unit. In fact, NFPA 110 Annex A specifically warns that weekly unloaded running can cause wet stacking.
• Monthly exercise under load for at least 30 minutes, at either a minimum of 30% of nameplate kW or at the manufacturer-recommended minimum exhaust gas temperature, whichever is applicable to the specific installation.
• Annual load bank test if the monthly load thresholds aren’t consistently met. The step profile depends on the edition of NFPA 110 your AHJ enforces. Earlier editions required 25% / 50% / 75% over 2 hours; NFPA 110-2025 requires 50% for 30 minutes plus 75% for 60 minutes.
• Triennial 4-hour load test for diesel EPSS, which can be combined with the annual test per NFPA 110 provisions for combined testing.
• Annual fuel quality testing to ASTM D975 or equivalent for diesel systems. (See how long diesel fuel lasts for the practical side of fuel aging.)
• Periodic circuit breaker exercise and testing. Annual exercise of main and feed breakers, with breakers rated over 600 V requiring more frequent exercise and periodic simulated-overload testing.

Healthcare facilities face additional scrutiny under Joint Commission standards and CMS Conditions of Participation, which impose their own testing and documentation requirements layered on top of NFPA 110.

Common Commissioning Failures and How to Prevent Them

After decades of watching commissioning projects across oil and gas, data centers, telecom, healthcare, marine, and crypto mining installations, the same failure modes appear over and over:

Failure	Root Cause	Prevention
First-start oil starvation	Pre-lube step skipped; shipping plug left in	Mandatory 60-second pre-lube with pressure verification
Voltage dip exceeds tolerance on motor start	Alternator or engine undersized for step load	ISO 8528-5 step load test during FAT, before shipment
Overheat at 75% load	Restricted airflow, wrong radiator, obstructed louvers	Full-duration 2-hour 100% load test in installed configuration
ATS fails to transfer	Control wiring pulled to wrong terminals	Point-to-point ring-out during pre-commissioning
Reversed phase rotation	Cables landed without rotation check	Phase rotation meter check before load is applied
Warranty denied after failure	Commissioning report missing or incomplete	Signed FAT and SAT documents filed with OEM
AHJ rejection at occupancy	NFPA 110 test skipped or undocumented	2-hour load test scheduled with AHJ witness
Wet stacking in first year	Monthly test at <30% load only	Load bank when the service load is too light
Fuel gelling in winter or water contamination	Tank never sampled; fuel older than 12 months	Annual ASTM D975 fuel quality test
Battery failure at 18 months	Charger float voltage wrong; battery age unknown	Verify charger output during commissioning; record battery date

Testing Considerations for Used and Surplus Generators

New installations aren’t the only place commissioning matters. Buyers of used, rebuilt, or surplus industrial generators, which is a large share of the oil and gas, marine, crypto mining, and distributed-power markets, need a slightly different testing approach.

Before purchase, a used unit should come with:

• Hours of operation, verified from the ECM download where available
• Original OEM manuals and, if possible, service history
• A recent load bank test report, ideally within the last 12 months
• Insulation resistance readings
• Engine oil analysis results (for diesel units)
• Photos of the unit running with the controller display visible

On receipt, re-run the full pre-commissioning checklist. Transit shock on a used unit can dislodge fasteners, crack radiator tanks, or shift alternator alignment. Re-megger the windings. Re-test protection set-points because previous settings may not match your application.

During SAT, load-bank a used unit to at least 100% for at least 2 hours. A generator that has been sitting in a yard for 18 months at 30% of its original service load will reveal any latent problems inside the first hour of full-load operation, which is exactly when you want to know about them: before the asset is in service.

This is the reason Depco’s yard process in Houston includes bench testing and certification on a significant portion of its inventory before shipment, and it’s the reason a buyer should always ask for the test sheet by serial number. For more on what to check when evaluating a used industrial engine or generator, see our buyer’s guide to sourcing industrial diesel engines and rebuilding vs. buying new.

Who Should Be on the Commissioning Team?

A properly staffed generator commissioning effort has five roles, even on smaller projects. One person can wear more than one hat on a simple installation, but the roles themselves don’t go away:

1. Commissioning agent (CxA). Leads the process, owns the test procedures, witnesses critical tests, signs the final report.
2. Installation contractor. Responsible for mechanical and electrical installation, pre-commissioning punch list completion.
3. Manufacturer’s factory representative. Configures controls, sets protection, performs first start, signs off on warranty activation.
4. Owner’s representative. Witnesses tests, accepts handover, ensures operations and maintenance staff are trained.
5. Authority Having Jurisdiction (AHJ). Witnesses the NFPA 110 acceptance test and signs off for occupancy (for EPSS installations).

For complex installations (paralleling systems, multi-genset plants, data center 2N topologies), add a controls integrator for the switchgear and paralleling controls, and consider an independent third-party testing firm for the load bank work.

Standards and Codes to Have on Hand

The documents below are the working references for any professional generator commissioning program. Know which editions your AHJ has adopted.

• NFPA 110: Standard for Emergency and Standby Power Systems
• NFPA 99: Health Care Facilities Code
• NFPA 37: Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines
• NFPA 70 (NEC): National Electrical Code, particularly Articles 445 (generators), 700, 701, 702, and 708
• NFPA 30: Flammable and Combustible Liquids Code (fuel storage)
• NETA ATS: InterNational Electrical Testing Association Standard for Acceptance Testing Specifications
• IEEE 115: Test Procedure for Synchronous Machines
• ISO 8528-5: Reciprocating Internal Combustion Engine Driven Alternating Current Generating Sets, Part 5: Generating Sets (performance)
• ISO 8528-6: Test methods
• ASTM D975: Standard Specification for Diesel Fuel Oils
• Joint Commission EC standards: for healthcare facilities
• CMS Conditions of Participation: for Medicare/Medicaid-participating facilities

Frequently Asked Questions

Below are commonly asked questions related to testing and commissioning lifecycle for industrial diesel and natural gas generator sets.

What is the difference between testing and commissioning a generator?

Testing is any individual verification activity: measuring an insulation resistance, running a load bank, checking an alarm. Commissioning is the structured, documented process that strings those tests together in the correct order, gates progression on their results, and produces a written record that the entire system works as specified. Testing is the activity; commissioning is the program. For the load bank portion specifically, see our guide to generator load bank testing.

How long does generator commissioning take?

For a single standalone generator in a straightforward installation, full commissioning from arrival on site through handover typically runs 3 to 5 working days, including the NFPA 110 2-hour load test with the AHJ. Complex paralleling systems, multi-genset plants, or installations with large switchgear can take 2 to 4 weeks. FAT at the factory is usually 1 to 2 days per unit.

Do I need a load bank for a generator that will always see the full facility load?

Yes, for two reasons. First, even a fully loaded facility rarely presents exactly the right load profile for a structured acceptance test: you need the ability to hold a precise percentage for a measured duration. Second, ongoing annual load bank testing is required by NFPA 110 for any EPSS that does not reliably reach 30% of nameplate kW during monthly exercise, and by many insurance carriers regardless.

Who is the Authority Having Jurisdiction for my generator?

The AHJ is whichever agency is responsible for enforcing the applicable codes at your location. It can be the local fire marshal, the state health department, a CMS surveyor, The Joint Commission, or a combination. For healthcare facilities, multiple AHJs often have overlapping authority, and you must satisfy all of them. Identify your AHJ(s) early in the design phase, not during commissioning.

What if I’m buying a used generator? Is commissioning still required?

Yes. A used generator arriving on your site is, from the code and warranty perspective, indistinguishable from a new one. It needs to be installed, pre-commissioned, acceptance-tested, and handed over with a full documentation package. The FAT equivalent is the dealer’s in-yard load bank test and certification report. The SAT is the same as for a new unit. Skipping commissioning on a used unit is the single most common source of in-service failures.

Closing Thought

Commissioning is where a generator purchase stops being a capital expense and starts being an insurance policy. It is the only point in the asset’s life when the system is in the shop, under controlled conditions, with the right people present, and with the budget and calendar to fix what is wrong before it matters. Every hour spent on a thorough FAT, SAT, and load bank program is an hour that pays back the first time the utility drops.

If you’re specifying a new install, evaluating a used generator for purchase, or building out a testing program for an existing fleet, the principles above (clear phases, written procedures, measured data, documented handover) are the same across diesel, natural gas, prime, and standby applications. What changes are the exact load profiles, the applicable code editions, and the test durations. The discipline is constant.

Depco Power Systems buys and sells commercial and industrial diesel and natural gas generator sets, engines, power units, and transfer switches worldwide, with bench testing and certification on a significant portion of inventory before shipment. To learn more about our testing and certification process or to discuss a generator purchase, contact our sales team in Houston.