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Power System Testing for Assured Performance

Does your UPS system maintain continuity during a power disturbance?

Access, Inc. Michigan suggests a load bank test at the initial start-up of any GenSet, or generator and ATS (automatic transfer switch) system. And, to maintain this equipment, an annual load bank performance test is also suggested.


A load bank provides a consistent and repeatable electrical load that can be accurately controlled, measured, and recorded. Load banks convert or dissipate the resultant electrical energy into thermal or heat energy. A basic load bank utilizes precise resistive elements cooled by an integral fan. Load banks provide a stable and controllable load for determining performance characteristics of a power system. They can be as simple as a single resistor or as complicated as a resistive/reactive load system with computer control. Their main category of use is with generator sets, however, there are a number of other applications where they may be used.


A resistive load bank can be used to fully test the generator set at 100% nameplate kW rating. It will also fully load the generator cooling, fuel, and exhaust systems. Only 80% of the generator set nameplate kVA rating can be achieved when utilizing a resistive unit. The resistive load bank will provide a unity or 1 power factor (PF) load to the system under test. Resistive units are predominantly used for AC voltages, however specifically designed DC load banks are also available.

An inductive load bank is normally used in conjunction with a resistive unit to provide a lagging power factor load test. This provides the capability to test the generator set fully at 100% nameplate kVA rating. Inductive load banks add inductance to the load and therefore reduce the PF to less than unity (lagging). Inductive load banks are rated in kilovolt-amperes reactive (kVAR). See Figure 1.

A capacitive load bank is normally used in conjunction with a resistive unit to provide a leading power factor load test. Capacitive load banks incorporate industrial capacitors and increase the PF to above unity (leading). Capacitive load banks are rated in kVAR.

A combined load bank usually consists of both resistive elements and inductors that can be used to provide load testing at non-unity PF (lagging) including the capability to test the generator set fully at 100% nameplate kVA rating. Combined load banks incorporate resistors and inductors all in one construction which can be independently switched to allow resistive only, inductive only, or varying lagging power factor testing. Combined load banks are rated in kilovolt-amperes (kVA). It’s worth noting that combined load banks can provide resistive, inductive, and if specified, capacitive functions.


The main reason for using a load bank is to test power sources. Load banks are also effectively used to verify the performance of heating, ventilation, and air conditioning systems. They can be applied to the following power testing purposes:

Maintenance and Repair Verification.
A load bank is an essential service and maintenance tool. The major reason why a generator or uninterruptible power supply system fails to perform is inadequate or improper maintenance. The correct operation of the standby power system can only be guaranteed with regular scheduled maintenance routines. Following maintenance or repair, a load bank is used to verify the functional capabilities of the entire power system.

Installation Acceptance / Commissioning / Witness Testing.
When a new power system is installed, it is important to verify that the entire system will perform as designed. When a generator set is installed into a building, load testing verifies the design and performance of the engine’s cooling, fuel and exhaust systems. Load testing is also used to verify that Uninterruptible Power Supplies can provide adequate amounts of power over required time-frames. If any of these systems are not designed and installed properly, testing using a load bank will identify performance deficiencies so that they can be proactively corrected.

OEM Product Sign Off and Engineering Design Development.
ISO8528 is the best practice for testing and verifying AC generator sets driven by reciprocating internal combustion engines for land and marine use. It specifies the test methods for characterizing the performance of an entire generator set. New product designs in engines, alternators, or batteries require verification of load carrying capabilities, fuel consumption, cooling, and the performance of exhaust systems and Automatic Voltage Regulators.

Code Compliance Verification.
Mission critical facilities are typically required to comply with various codes and standards regarding local testing. The most common load testing regulations are contained in National Fire Protection Agency (NFPA) codes as follows:

NFPA 99 – Healthcare Facilities Code – Healthcare facilities must exercise Emergency and Standby Power Systems under load and operating temperature conditions for at least 30 minutes at intervals of not more than 30 days.

NFPA 110 – Standard for Emergency Generator Systems – Monthly testing is performed on generators whose failure could result in injury or death. If a generator fails a monthly test, it should be tested annually for two continuous hours using a load bank. Under the continuous test, the generator should be operated at 25% of the nameplate kilowatt rating for 30 minutes, at 50% of the kilowatt rating for 30 minutes, and at 75% of the kilowatt rating for 60 minutes.


Load bank controls can vary from simple pilot relays, toggles, and decade switches to a multi-function embedded system that provide different types of load, full instrumentation, and data capture. Some control systems can network multiple load banks of varying capacity by a single remote controller or PC. Digital toggle control allows for synchronous load applications which is important for generator voltage regulator and governor testing.

Many manufacturers offer remote hand-held touch screen controllers that feature flexible load profiling and full digital monitoring. Various optional software packages provide sophisticated control along with transient speed instrumentation, and full data acquisition reporting with graphical displays. Software control can also log real-time data, such as crest recovery times and percentage error. These real-time values are necessry for ISO8528 compliance.

Modern load banks provide communication via MODBUS. MODBUS will allow the load bank to be integrated into existing building management systems through PLC, HMI, or SCADA platforms. 6 Site load correction and automatic load control features maintain minimum load values on the power source. These features will help prevent problems associated with light load, such as wet-stacking.

The ability to network load banks, where one remote controller or PC can control multiple load banks, can provide higher capacity testing where a single unit cannot provide adequate capacity.


Load banks are designed to dissipate a specific amount of power and must be designed to insure safety of the operator and equipment. A load bank must conform to the latest applicable International Electrotechnical Commission, National Electrical Manufacturers Association, National Electrical Code, and American National Standards Institute standards. Stationary and portable load banks should carry a third-party listing such as Underwriters Laboratory, Canadian Standards Association, or the European Union’s CE markings.


Load banks are a critical component for accurate power system testing. Emergency and backup power systems must conform to regulations which detail periodic load testing to ensure their compliance. In addition, load banks are used for maintenance and repair validation, acceptance testing of new power systems and OEM quality assurance. Major manufacturers offer load banks in various capacities, voltages and designs. Modern load banks feature many control options offering the user unmatched flexibility in precise and repeatable load profiling. Load bank testing ensures that the power source is operating properly and is performing as designed.

In conclusion, Access, Inc. is here to ensure that you get the best performace for your data center equipment. Both Access Inc. offices, Access, Inc. Wisconsin and Access, Inc. Michigan, have the know-how and experience to implement a load bank test, as well as, to provide Professional Assessment Services necessary to keep precision equipment at peak performance.

This article is adapted from the original which was posted May 1, 2019 and can be read in its entirety Here

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