Testing
Load Bank Testing for Generators in Gauteng
A load bank test connects an artificial electrical load to the generator and raises it in steps towards the set’s rating, while voltage, frequency, temperatures and pressures are recorded. It proves what a no-load run cannot: that the engine, cooling system, fuel supply, governor and AVR will hold up when the building depends on them. We arrange and quote load bank testing for each site across Gauteng.
- Stepped load up to the rating, or to the load you need proved
- Voltage, frequency, temperatures and pressures recorded at each step
- Finds faults that only appear under sustained load
- Helps burn off wet stacking in lightly loaded diesels
Established 2006
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1 kVA–20,000 kVA capability
Why a no-load test is not enough
Many standby generators are exercised without load: the controller starts the set on a schedule, often once a week, it runs briefly and stops. That proves the battery, starter and controller, but it says nothing about whether the cooling system copes after an hour at full output, whether the fuel system delivers at full demand, or whether the alternator holds its voltage when a large motor starts.
Load shedding added a second problem. Many sets now run for hours every day on a fraction of their rating: a generator sized for a whole building may carry only the lights and a few computers overnight. A diesel run that lightly never gets hot enough to burn all its fuel, and unburnt fuel and carbon collect in the exhaust. That is wet stacking, and a sustained run at a higher load on a load bank is a standard way to burn it off.
What a load bank test proves
| Check | What it proves |
|---|---|
| Output at the rated or required load | What it provesThe engine reaches the kW you need without labouring, smoking or tripping |
| Voltage on each phase at every step | What it provesThe alternator and AVR hold voltage as load rises |
| Voltage dip and recovery when load is switched on | What it provesHow quickly the AVR responds to a sudden load, such as a motor starting |
| Frequency at each step and after load changes | What it provesThe governor and fuel system hold frequency close to 50 Hz as load rises, within the droop the governor is set for, and recover quickly after a step |
| Coolant temperature over a sustained run | What it provesThe radiator, fan and coolant hold temperature at full output, not just for a few minutes |
| Oil pressure and engine behaviour | What it provesWear and faults that only show when the engine works hard |
| Exhaust colour and residue | What it provesWhether wet stacking clears, or whether smoke points to injection or air-supply problems |
| Alarms and the output breaker | What it provesNo warnings or nuisance trips at normal load, and a breaker that carries its rated current |
Types of load bank
Resistive and reactive load banks
Resistive load banks
Resistive elements cooled by fans absorb real power (kW) at a power factor of 1. This loads the engine, fuel system and cooling fully, and suits most routine tests and wet-stacking burn-offs. It does not stretch the alternator to its full kVA rating: at a power factor of 1, the rated kW draws less current and needs less excitation than a real building load does, so the alternator and AVR are not fully tested.
Reactive load banks
A resistive-reactive load bank adds inductive load so the generator runs at a lagging power factor, typically 0.8, which is how most sets are rated. This tests the alternator and AVR at full kVA as well as the engine at full kW, and is used for commissioning and for critical sites where the whole set must be proved.
Testing on the building load instead
A building load test switches off the mains, or simulates a mains failure, and lets the generator take the real load through the changeover. It is valuable because it also proves the start sequence and the automatic transfer switch, and every standby site should do one from time to time.
Its limit is that the load is whatever the building happens to draw at that moment, often well below the generator’s rating, and it cannot be stepped or held at a chosen level. A load bank gives a controlled, repeatable test up to the rating, without putting the building onto generator power.
- Building load test: proves the changeover and the real load
- Load bank test: proves the full rating, step by step
- Many maintenance plans use both
Who needs a load bank test
Not every generator needs one every year. These are the situations where it earns its place.
- Critical sites such as clinics, server rooms, cold rooms, water pumping and security systems, where a generator failing under load is not an option
- After major repairs: injector or injection pump work, an engine overhaul, a rewound alternator, or a new governor or AVR
- At commissioning, to prove a new generator installation before handover
- As part of a maintenance plan, often once a year for standby sets
- Sets that run lightly for long periods and show oily residue or black dribble at the exhaust joints
- Before relying on a used or long-idle generator
- Where the load has grown since the set was chosen; the kVA sizing guide shows how to check the headroom
Factories, mines and plants that run production on standby power are covered under industrial generator services.
Process
How a load bank test is done
- 01
Plan the test
We confirm the generator’s rating, voltage and phases, where the load bank can connect, the cable route, and a time that will not disturb the site.
- 02
Check the set first
Oil, coolant, fuel level, belts, battery and leaks are checked before any load goes on, so the test never pushes a set with a known fault.
- 03
Connect
The load bank is connected at the generator’s output, separate from the building’s circuits, and its hot air discharge is kept clear of people, vehicles and anything that can burn.
- 04
Step the load
Load is applied in stages, for example a quarter of the rating at a time, and each step is held while the readings settle and are recorded.
- 05
Hold and watch
The highest step is held long enough for temperatures to stabilise, which is where cooling and fuel problems show themselves.
- 06
Cool down and report
The load comes off, the engine runs unloaded to cool, and you receive the readings, our findings and a free quotation for any repairs.
FAQ
Frequently asked questions
How often should a generator be load bank tested?
For standby generators protecting critical loads, once a year is a sensible default, plus after any major repair. Generators that regularly carry a heavy real load may need it less often; sets that run lightly and show signs of wet stacking may need it more often.
Will the test interrupt my power?
The load bank is connected to the generator rather than the building, so the test does not need the building on generator power. Connecting and disconnecting may need a short planned interruption on some installations, and we agree that with you first.
Can a load bank test damage my generator?
A generator in sound condition is built to carry its rating, and the load is raised gradually with the readings watched throughout. If a temperature or pressure moves out of range, the test stops. A test can expose a weak part, such as a tired radiator or a worn injector, but finding it during a planned test is far better than finding it during an outage.
Does a load bank test fix wet stacking?
A sustained run at higher load usually burns off the build-up. If it keeps coming back, the set is probably running too lightly for its size day to day, which our page on wet stacking explains.
How long does a load bank test take?
It depends on the generator’s size, how many steps are tested and how long the full-load hold runs. Much of the visit is setting up, connecting and stepping the load. We agree the test plan and its timing before the day.
Does the test have to reach 100% of the rating?
Not always. A routine test can stop at the load your site actually needs proved, plus headroom. For commissioning, after a major repair or on a critical site, testing up to the rating is normal.
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