Diesel Generator FAT Staged Load Test Procedure

A diesel generator FAT load test should start with an approved test plan, safety and connection checks, and no-load stabilization. Apply load progressively, hold each agreed stage, and record electrical, engine, thermal, alarm, and observation data. Perform transient or overload tests only when the contract, rated operating category, manufacturer limits, and approved procedure require them.

Define load stages, hold periods, acceptance criteria, instruments, and witness points before starting.
Record synchronized readings at no load, every load stage, transients, and shutdown.
Stop safely when an alarm, leak, unstable reading, unsafe temperature, or agreed limit is reached.

Approve the test plan

Confirm the tested configuration, rated voltage, frequency, power factor, operating category, load stages, hold times, acceptance limits, and witness responsibilities. Use the complete diesel generator FAT guide to place this test within the wider factory inspection.

Complete safety and equipment checks

Verify fuel, oil, coolant, ventilation, exhaust, guards, grounding, cable rating, phase sequence, emergency stop, protection settings, load-bank capacity, and instrument calibration. Record completion in the FAT test item checklist. Only authorized personnel should control energized equipment.

Start and stabilize at no load

Start the set, confirm oil pressure and charging, inspect for leaks or abnormal vibration, and allow voltage, frequency, temperatures, and pressures to stabilize. Test protective functions only as permitted by the approved plan.

Apply progressive load stages

Apply the contract-defined sequence rather than assuming universal percentages. At every stage, wait for the specified stabilization condition and record kW, kVA, power factor, phase voltage and current, frequency, oil pressure, coolant temperature, fuel indication, alarms, smoke, vibration, and ambient conditions.

Run steady-state, transient, and overload checks

Observe stability during each hold. Apply step loads and measure voltage and frequency dip and recovery only where specified. An overload run is not automatic: confirm that it matches the declared rating, engine and alternator capability, contract, and approved test method.

Unload and shut down under control

Reduce load in planned stages, open the load connection, run the prescribed cool-down period, and stop the set. Record final temperatures, pressures, alarms, leaks, abnormal conditions, and post-test fluid levels.

Resolve deviations and sign the record

Identify failed readings without deleting original results. Document the cause, corrective action, affected test scope, and retest result. Witnesses should sign an agreed load test report format with instrument IDs and attachments.

Are fixed 25%, 50%, 75%, and 100% stages mandatory?

No. They are common planning points, but the signed specification and approved procedure must define the actual sequence and duration.

When should overload testing be performed?

Only when contractually required and permitted by the declared rating and manufacturer limits. The load, duration, safeguards, and acceptance criteria must be approved beforehand.

What evidence should the buyer receive?

Request the approved procedure, calibration evidence, timed readings, alarm and deviation records, photographs where agreed, retest results, and signed witness acceptance.

Standards, safety, and acceptance evidence

The International Organization for Standardization explains in ISO 8528-5 that generating-set performance includes steady-state and transient characteristics. This supports defining the performance class and agreed limits before FAT rather than judging a test from rated kW alone. ISO standards are voluntary unless incorporated into a contract or applicable rule.

The ISO test-method framework in ISO 8528-6 supports using an agreed measurement and test basis. For buyers, this means the report should identify the method, operating conditions, instruments, and results needed to reproduce the acceptance decision.

For workplaces under United States jurisdiction, the Occupational Safety and Health Administration's 29 CFR 1910.147 hazardous-energy rule defines controls for servicing where unexpected energization could cause injury. OSHA's 29 CFR 1910.333 addresses work practices around live electrical parts. These sources support controlled access, qualified personnel, isolation procedures, and a documented emergency response during load-bank work; local rules must also be checked.

Minimum data table

Phase	Essential evidence
No load	Start time, voltage, frequency, pressures, temperatures, leaks, alarms
Each stage	Time, kW, kVA, power factor, phase voltage/current, frequency, thermal and engine readings
Transient	Applied step, minimum/maximum values, recovery time, response
Shutdown	Unloading sequence, cool-down, alarms, final inspection