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Load Bank Team Saves the Day for Generator Services Contractor

Standby generators may not serve their purpose unless businesses ensure their operation through regular preventive maintenance. Load bank testing is an integral part of best maintenance practices. These tests help extend a generator’s engine life and ensure it runs reliably at the rated horsepower if utility power fails. Most maintenance organizations call in a generator services contractor at least once a year to perform load bank tests.

A commercial building required preventive maintenance on three 2500-kW standby generators. The property manager asked their generator services contractor to perform the necessary annual testing and maintenance. 

Failure during critical testing

The generator services contractor experienced challenges with a supplier whose equipment failed during the tests of standby generators. The supplier could not provide a technician to repair the equipment in time to complete the test. The delayed response created a major disruption for the client, which faced the additional expense of rescheduling maintenance personnel and inconvenience of conducting the test on a subsequent weekend.

Given the circumstances, the contractor lost faith in the supplier and decided to contact Sunbelt Rentals. 

Right response, right equipment

The generator services contractor provided the project scope and information on the generators to be tested. In consultation with the contractor, the Sunbelt Rentals team spec’d the project and provided a solution recommendation on short notice.

The solution included a 3-MW load bank, 2500-Kva transformer, cabling, and accessories. For standby generators in service, bringing a generator up to full load can take anywhere from 4 hours to 8 hours or more. A Sunbelt Rentals technician remained on site during startup to ensure everything ran smoothly and to resolve any issues that might arise. In addition, the technician assisted with setup, cable rollout, and conducting the test. Helping with cable rollout reduced the need for contract labor, saving time and money. Aside from load testing the generators, the service contractor also performed other routine annual maintenance tasks, such as changing the oil, filters, and belts. 

Although maintenance managers exercise generators frequently throughout the year, they are typically run at less than their rated full load capacity. This can result in “wet stacking,” which is why load bank testing is critical to the life of standby generators.

Wet stacking

Diesel engines use hot compressed air in the cylinder to vaporize and ignite the fuel. If the engine is run without sufficient load, the air never reaches the optimal temperature and the fuel doesn’t burn completely. Vaporized fuel and soot then accumulate in the exhaust and form a dark, thick liquid. When a diesel or other engine drips this viscous substance from the exhaust pipes—which are also known as “stacks”—the result is wet stacking. Over time, wet stacking can seriously impair engine performance.


The load bank test ran smoothly over the weekend, and the building was back in business the following Monday. The maintenance manager and generator services contractor were extremely pleased with the quality of the Sunbelt Rentals equipment and customer service provided. As a result, the generator services contractor now uses Sunbelt Rentals as their trusted equipment provider. The year following the initial tests, Sunbelt Rentals was asked to return for tests that proved equally successful.

Sunbelt Rentals provides load banks to simulate real world conditions for power supplies and critical power systems, wind and solar farms, substations and transformers, naval and marine generators, and Integrated Systems Testing (IST) of grid power. We have comprehensive solutions to protect your facility and keep your projects on schedule from start to finish.