What Is a Load Bank?

Testing power sources, such as uninterruptable power sources (UPS) and diesel generators, ensure that these devices will provide the required amount of power when needed. A load bank tests these power sources by developing an electrical load. Various load configurations permit testing under different conditions.

A load bank is a self-contained device that has the load elements, controls and cooling systems it needs to operate built-in. Power is delivered to a load bank, which then consumes the electrical power by applying it to a power source and either converting or dissipating the source's power output. Load banks use the energy produced to protect, support or test a power source while a "real" load or actual building load uses energy output productively.

What Is the Purpose of a Load Bank?

Load banks ensure the quality and reliability of your emergency power sources. They verify the accuracy of the generators' output capacities by creating a variety of different loads that replicate real-world use.

If you own, sell or operate generators, especially for backup power, you need to test them regularly. Without testing, you cannot be assured the generator will provide the required power when the lights go out. Many facilities require load tests of all backup power sources. Prime power generators benefit from load bank use, particularly in lightly loaded situations.

What Does a Load Bank Do?

A load bank develops an electrical load. Load banks are absolutely essential for emergency sources of power, as they verify the power source's rated output capabilities before the power source is called into actual use. A load bank should mimic the real load a power source would see during an actual use scenario. The devices usually have different levels of load, which allows critical systems to be tested under a variety of conditions.

Who Uses Load Banks?

You need this type of testing bank if you have generators or uninterruptable power sources in your business. Best practices for testing emergency power sources is regular load bank tests.

If you have diesel generators on-site, you may use a load bank to augment lightly loaded situations and keep your generator running properly. Wet stacking occurs when unburned fuel remains inside the system. The unburned diesel condenses and combines with soot in the exhaust system, leading to wet deposits on exhaust components. Left unchecked, wet stacking reduces engine efficiency until it requires a complete overhaul to restore its former power.

The best way to prevent this from occurring is to test the generator with a load bank, which enables you to complete two maintenance tasks with one action. Monthly testing is a requirement from the National Fire Prevention Association, in its Standard for Emergency and Standby Power Systems. You must test the generator at full load to maintain the minimum exhaust temperature recommended by the manufacturer. An alternative test allows you to use 30% more than the rating on the generator's nameplate for at least half an hour.

A novel use for these banks is for renewable energy sources. The Hawai'i Natural Energy Institute (HNEI) has incorporated a load bank into the power system on the island of Moloka'i. The island could not add more photovoltaic cells because it posed the threat of producing too much electricity and dropping the power produced by the island's diesel generators too low. The addition of a resistive load bank allows the island to add more solar cells because the load bank moderates the amount of power the island gets by absorbing any extra electricity produced.

Difference Between Resistive & Reactive Load Banks

Load banks come in many different forms based on the load they apply to the power sources they test. Resistive and reactive load banks are two primary forms. Each of these has its benefits for specific situations. Understand the differences between resistive and reactive load banks to find the best options for running tests on your power sources.

Resistive vs. Reactive Load Banks

Depending on your generators and how you use them, you may need resistive, reactive or both types of load banks. These devices put different kinds of loads on the generators. Resistive models are the most common, while reactive include inductive and capacitive power loads.

1. Resistive Load Bank Uses

Resistive load banks draw power from a generator in the same way lights or appliances would. These testing devices work well with generators used for general power purposes that involve transforming electricity into heat or light. Light bulbs, lamps and space heaters are examples of tools that convert electrical energy into heat.

These types of load banks draw a specified real power load, in kW, on the generator to ensure the operation of the power supply's cooling system, exhaust and engine operation. They do not test the generator for full apparent power in kVA, which is what a reactive load bank tests.

2. Reactive Load Bank Uses

Reactive load banks can simulate inductive loads, often used commercially in construction or in backup power supplies. Inductive loads create a lagging power factor, whereas capacitive loads generate a leading power factor. Of these two types, inductive appears more commonly in objects that turn power into motor operation through magnetism.

For facilities that rely on emergency generators to run equipment for business-critical operations or life support, such as data centers and hospitals, reactive load bank testing is the most effective.