In Short
A load bank is equipment that draws a controllable electrical load from a generator, a UPS or a switchboard so the system can be tested without real consumers. It is used for factory acceptance, commissioning and regular exercise of standby plant, proving that a generator can carry its rated load before it is needed.
A generator that has never carried its rated load has never been proven. A load bank is the equipment that proves it: a bank of resistors - and, for a full test, reactors or capacitors - that draws a controllable electrical load from a generator, a UPS or a switchboard so that the whole system can be run at any load up to its rating, for as long as the test requires, without needing the real consumers. Factories use it to accept a set; sites use it to commission and to exercise standby plant that otherwise runs unloaded.
Resistive, Reactive and Resistive-Reactive
A resistive load bank converts the electrical power into heat in resistor elements cooled by its own fans; it tests the engine, the governor and the alternator, which is what most acceptance tests ask for. A reactive load bank adds inductive load - reactors - so that the set is tested the way real motors and transformers load it, which stresses the alternator and the voltage regulator in a way a resistive load does not. A resistive-reactive load bank combines both in one unit.
Capacitive load banks test the kind of load that UPS systems and some data center loads present. A load bank is built in steps, so the test can move through the load curve point by point.
The Tests a Load Bank Serves
At the factory, the acceptance test of a generator set runs it at stepped loads up to full load, records voltage, frequency, temperatures and fuel consumption, and applies sudden load steps to check how the set responds. On site, the commissioning test repeats this through the real switchgear and transfer switches, and a data center or a hospital usually runs the complete standby system for hours under load bank before it is accepted.
Afterwards the load bank keeps the set healthy. A diesel that runs unloaded or lightly loaded during monthly tests never reaches its operating temperature; unburnt fuel and carbon collect in the exhaust - wet stacking - and the injectors, the turbocharger and the exhaust system suffer. A periodic run under load on a load bank burns it off, which is why standby plants have a load bank test in their maintenance schedule.
Portable, Trailer or Permanent
Portable and trailer-mounted load banks are brought to the site for commissioning and for the yearly test, connected to the generator breaker with cables. Permanent load banks are installed next to the set or on the container, wired through a dedicated breaker, and run from the generator control or the building management system on a schedule; they are chosen where the monthly test must be done under load without bringing equipment in - data centers, hospitals, remote sites and generator containers delivered as complete plants.
The size of a permanent load bank is a decision: a full-rating bank tests everything but costs more and takes space; a smaller bank prevents wet stacking and exercises the system without proving the full capacity. AXON builds dummy load banks as stand-alone units and integrated into generator containers, matched to the test regime of the site.
In short
- A load bank draws a controllable load so a generator can be tested without consumers
- Resistive for the basic engine test, reactive for motor-type loads, capacitive for UPS-type loads
- Factory and site acceptance tests: load steps, transient response, hours under load
- Prevents wet stacking in standby sets that otherwise run unloaded
- Portable for commissioning and yearly tests; permanent for scheduled testing
- AXON builds dummy load banks stand-alone or built into containers
What to send with an enquiry
- Generator rating in kW / kVA, voltage and frequency
- Resistive only or resistive-reactive
- Portable, trailer or permanent installation
- Control: local, from the generator controller, or from the building management system
- Ambient temperature and the space available for the hot air
- Test regime: monthly exercise, yearly full test, commissioning
Questions we are often asked
What size load bank do I need?
It depends on the test. An acceptance test calls for the full rating of the set; routine exercising can use a smaller bank. Send the generator rating and the test regime and AXON proposes the size.
Is a resistive load bank enough?
For most engine and generator acceptance tests, yes. A reactive load tests the alternator and the voltage regulator the way real loads do; specifications for critical sites often ask for it.
Where does the heat go?
Into the air: everything the load bank draws from the generator leaves as hot air. It needs open space or a duct to the outside, and its intake must not be the generator's cooling air.
Can a load bank be used on a UPS?
Yes; load banks test UPS systems and battery autonomy as well as generators. Capacitive or resistive-reactive units cover the power factors UPS loads present.
How often should a standby generator be tested under load?
A regular short run, a periodic run under load bank and a full-load test every year are common schedules; the site's standard and the engine maker's recommendation decide.