Load Bank Testing for Standby Generators: Frequently Asked Questions

In load bank testing, a standby generator system receives an electrical load from a load bank. This tests system performance under simulated power outage conditions. Load banking is also used to resolve wet stacking – a condition in which diesel generators collect fuel in their exhaust pipes. If your facility has a diesel generator that may need load banking, but you need information about the process, the answers below could help.

How do I know if a generator needs load banking?

The need for testing is determined by a generator’s performance during its monthly test, which should last a minimum of 30 minutes. If a generator operates at less than 30 percent of its nameplate Kilowatt rating at any point during a 30-minute test period, it should be “exercised” annually by a load bank.

What does annual load banking consist of?

Annual testing guidelines are contained in National Fire Protection Association code 110 (NFPA 110). In brief, they require two consecutive hours of testing in which a generator performs as follows: 30 minutes of operation at 25% of the nameplate Kilowatt rating, 30 minutes of operation at 50% of the nameplate Kilowatt rating, and 60 minutes of operation at 75% of the nameplate Kilowatt rating.

Is different equipment used for different types of loads?

Depending on the characteristics of a facility’s load, there are five types of equipment that could be used:

1. Resistive banks, which deliver resistive loads;
2. Inductive banks, which deliver inductive loads;
3. Capacitive banks, which deliver non-linear loads;
4. Electronic banks, which deliver a solid state load;
5. Combination resistive/inductive banks, which are used for “full power system testing.”

Prime Power can determine the needs of your facility, supply the right equipment, perform testing, and supply you with a detailed report of your emergency power supply system’s (EPSS) performance.

How can I tell if a generator is experiencing wet stacking?

Clear signs of wet stacking in standby generators are: the accumulation of black ooze around exhaust pipe connections, and exhaust that remains black. If left unresolved, wet stacking could create a fire hazard. It could also reduce the lifespan of a generator motor by years. Prime Power can identify and resolve wet stacking.

Are there benefits to implementing a load bank onsite?

In most cases, outsourcing to a power service provider is more cost effective than buying a unit. However, when a load bank is needed for things in addition to generator testing, purchasing a unit may be the best option.

Why should I choose Prime Power?

Prime Power offers a mixture of experience and expertise that few industrial and commercial power service providers can match. In addition to having almost 30 years of experience in load banking and generator maintenance, we also deploy superior technology and hire only the best technicians in terms training and experience.

If you need:

• load banking,
• breaker testing,
• healthcare utility management,
• modernization and retrofits,
• new installations,
• arc flash analysis and training,
• infrared scanning, generator rentals,
• scheduled maintenance,

— Call Prime Power today.


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