One of the most common mistakes we see from Kenyan businesses is testing a generator by simply starting it and letting it idle for a few minutes. The engine runs. The lights come on. Everyone is satisfied. But when the next blackout hits and the building switches to generator power at full load — the unit overheats, trips on overcurrent, or shuts down on a fault it has never shown before. Load bank testing prevents exactly this scenario.
What Is a Load Bank?
A load bank is a self-contained device that creates an artificial electrical load — purely resistive, inductive, or a combination — that can be dialled up to any percentage of the generator's rated capacity. It connects directly to the generator's output terminals (or breaker panel) and draws real power, just like the building's actual electrical loads would.
Unlike running a generator on building load, a load bank gives the engineer complete, precise control over exactly how much load is applied and for how long. This makes it possible to test the generator at 25%, 50%, 75%, and 100% of its rated kVA in a controlled, measurable, and repeatable way.
Resistive Load Bank
Simulates heating and lighting loads. Pure resistive load, unity power factor. Used for basic capacity verification.
Inductive Load Bank
Simulates motor and compressor loads. Creates reactive power demand, testing the alternator's excitation system under realistic conditions.
Combination Load Bank
Combines resistive and inductive loads to simulate real-world mixed loads — the most accurate test for commercial facilities.
Why Idling Doesn't Prove Anything
A diesel engine that runs at low or no load is not being exercised properly. Several problems only appear under full load conditions:
Wet Stacking
When a diesel engine runs for long periods below 30% load, it cannot reach the combustion temperatures needed to fully burn the fuel. Unburned fuel (hydrocarbons) accumulates in the exhaust system, turbocharger, and sometimes the engine cylinders. The engine smokes excessively, loses power, and the injectors and piston rings become coated with carbon. Load bank testing at 75–100% capacity for 30 minutes clears wet stacking.
Cooling System Faults
A faulty thermostat or partially blocked radiator may not cause overheating at idle — the engine simply doesn't generate enough heat to expose the fault. Under full load, the same fault causes the engine to overheat and shut down. This is particularly common in generators that have sat unused for several months.
AVR and Voltage Stability Issues
The Automatic Voltage Regulator (AVR) controls the output voltage under varying load conditions. At low load, most AVRs perform well. At full load — especially with inductive motor loads — a poorly tuned or ageing AVR may allow voltage to sag or swing. This is only detectable under load bank conditions.
Fuel System Pressure Drops
A partially blocked fuel filter or a failing lift pump may deliver adequate fuel at idle but cause the engine to starve under full load. The symptoms — engine speed hunting, black smoke, or shutdown — only appear when the fuel demand is at its highest.
ATS Transfer Failure Under Load
The Automatic Transfer Switch (ATS) manages the transition from mains to generator power. Some ATS faults — particularly contact overheating and timing issues — only appear when the switch is carrying full current. Testing the ATS under no-load gives false assurance.
What Happens During a Load Bank Test
Pre-Test Inspection
The engineer checks oil level, coolant level, battery voltage, and fuel supply before starting. A baseline set of readings (voltage, frequency, current) is taken at no load.
Staged Load Application
Load is applied in stages — typically 25%, 50%, 75%, and 100% of rated kVA. At each stage, the generator is allowed to stabilise (usually 5–10 minutes) and a full set of readings is recorded.
Full Load Run
The generator runs at 100% load for a minimum of 30 minutes, or up to 2 hours for healthcare and critical facilities. This clears wet stacking and fully tests the cooling system.
Load Rejection Test
The load is suddenly removed (simulating a circuit breaker trip). The generator's governor and AVR must bring voltage and frequency back to stable levels within a few seconds. If they don't, a fault is identified and investigated.
Post-Test Report
The engineer produces a written report with all readings at each load stage, temperature logs, and any faults identified. This report is the evidence that your generator has been fully tested.
How Often Should You Carry Out a Load Bank Test?
The standard recommendation is once per year as part of your annual maintenance schedule. However, for facilities where power continuity is mission-critical — hospitals, data centres, telecommunications infrastructure — we recommend testing every 6 months.
Additionally, a load bank test should always be performed:
- After any major engine repair (to verify the repair before the generator returns to service)
- After a generator has been inactive for 3 months or more
- When there is unexplained black smoke or fuel consumption above expectations
- When a new generator is commissioned (factory acceptance testing)
- Before expiry of a generator warranty period
PowerProKe Load Bank Testing Service
We provide load bank testing services across Nairobi using calibrated combination load banks. All tests include a detailed written report with voltage, current, frequency, and temperature readings at each load stage. Our load banks cover single-phase and three-phase outputs from 30kVA to 1,000kVA.
Book a Load Bank Test — 0762 816 825
Eng. Okumu
Lead Technical Reviewer & Auditor
Specialization
Alternator Rewinding & Precision Servicing
Experience
18+ Years Industrial Power Systems
All information in this guide has been field-verified by our engineering team to meet current Kenyan Energy Regulatory Authority (EPRA) standards and manufacturer-specific diagnostic protocols for Perkins, Cummins, and Caterpillar systems.