Critical NFPA 110 Load Bank Testing Requirements: Annual vs. Triennial Testing
Load bank testing is an important part of maintaining the reliability and performance of an emergency generator system. However, there is often confusion about how long a generator must be tested, what load levels are required, and whether annual and triennial load bank testing requirements can be combined.
Many facility managers and building owners have recently asked about the difference between two-hour and four-hour load bank tests, as well as whether a test must follow a stepped-load sequence such as 30%, 50%, and 80%.
The answer depends on the specific NFPA 110 testing requirement being performed.
At Weld Power Generator, we have historically standardized our load bank testing approach by performing stepped-load testing whenever practical. This provides valuable operating data and allows us to evaluate generator performance at multiple load levels beyond the minimum requirements.
However, as more facilities choose to separate their annual supplemental load bank testing from their required 36-month testing, it is important to understand what each test actually requires.
Table of Contents
Why Understanding the Testing Requirements Matters
Not every load bank test has the same purpose or requirements.
The appropriate test duration and load profile depend on factors including:
- Whether the generator achieves sufficient loading during its monthly exercise
- Whether annual supplemental load bank testing is required
- Whether the test is being performed as part of the required 36-month testing cycle
- The assigned Class duration of the emergency power supply system (EPSS)
- The amount of building load available during testing
- Whether annual and triennial testing are being combined
Understanding these differences helps facility managers request the appropriate scope of work and ensures testing is performed at the correct parameters.
1. Annual Supplemental Load Bank Testing
When Is It Required?
Supplemental load bank testing is required when the generator does not achieve at least 30% of its nameplate kW rating, or the manufacturer’s recommended exhaust gas temperature, during its monthly exercise.
The purpose of this testing is to ensure the generator operates under sufficient load to help verify performance and address the potential effects of extended operation at light load.
Annual Test Requirements
When supplemental testing is required, the test is performed annually and includes:
- 50% of the generator’s nameplate kW rating for 30 continuous minutes
- 75% of the generator’s nameplate kW rating for 60 continuous minutes
The required loaded portion of the test is 1.5 continuous hours.
A warm-up period of approximately 30% load for 10 to 15 minutes and an unloaded cool-down period of at least 5 minutes are commonly recommended. However, these periods are not included in the required 1.5-hour test duration.
2. Triennial 36-Month Independent Testing
The second major testing requirement is the independent 36-month test, commonly referred to as the triennial test.
Purpose of the Triennial Test
The purpose of this test is to verify that the emergency power supply system can sustain operation for the required duration of its assigned Class.
For a Level 1 EPSS, this testing is performed every 36 months.
Test Duration
The generator must operate continuously for the system’s assigned Class duration, up to a maximum of four continuous hours.
The actual required duration depends on the Class designation of the system.
Diesel Generator Load Requirements
For diesel-powered generators, the generator must maintain a minimum load of:
- 30% of the generator’s nameplate kW rating, or
- The manufacturer’s recommended exhaust gas temperature
for the duration of the test.
If the facility does not have sufficient building load to reach the required minimum loading, a supplemental load bank may be used.
Does a Standalone Triennial Test Require Stepped Loading?
No.
When the 36-month test is performed as a standalone triennial test, NFPA 110 does not require the generator to be tested using a 30%-50%-80% stepped-load sequence.
The test also does not automatically require the generator to reach 75% or 80% load.
If the building load is already sufficient to maintain at least 30% of the generator’s nameplate kW rating, a supplemental load bank may not be necessary.
3. Combining Annual and Triennial Testing
In many cases, the annual supplemental load bank test and the 36-month triennial test can be combined into a single testing event.
This is often the most efficient approach because one test can satisfy both requirements.
Combined Test Requirements
The combined test is performed every 36 months and consists of:
- The first 3 hours: Maintain at least 30% of the generator’s nameplate kW rating
- The final 1 hour: Increase the load to at least 75% of the generator’s nameplate kW rating
The total test duration is four continuous hours, or the system’s assigned Class duration, whichever is less.
This combined approach allows the test to satisfy both the 36-month endurance testing requirement and the annual supplemental load bank testing requirement.
What Does This Mean for a “4-Hour Load Bank Test”?
One of the most important distinctions is that a request for a “4-hour load bank test” does not automatically mean the generator must be tested using a 30%-50%-80% stepped-load sequence.
Before performing the test, it is important to determine the intended scope:
Standalone Triennial Test
A standalone 36-month test generally requires the generator to maintain the minimum required load, typically at least 30% of nameplate kW for a diesel generator, for the required duration.
A stepped-load sequence is not automatically required.
Combined Annual and Triennial Test
When the annual supplemental test and the triennial test are combined, the test includes the required higher-load portion at the end of the test.
For the combined approach, the generator operates at a minimum of 30% load for the first three hours and then at least 75% load for the final hour.
Why Weld Power Often Performs Stepped Load Testing
Although stepped-load testing is not required for every test scenario, Weld Power has historically used stepped loading whenever practical.
Testing at multiple load levels can provide additional operating data and give technicians a more complete picture of generator performance.
Depending on the scope of work, a stepped-load test may help evaluate how the generator performs as load is progressively increased. This can provide valuable information beyond simply verifying that the generator can maintain a minimum required load.
However, the appropriate test profile should always be based on the specific testing requirement and the scope of work being performed.
The Bottom Line
Not all load bank tests are the same.
The testing requirements depend on whether the generator is undergoing:
- Annual supplemental load bank testing
- A standalone 36-month triennial test
- A combined annual and triennial test
The most important thing is to identify the purpose of the test before determining the test duration and load profile.
If a facility is scheduled for a “4-hour load bank test,” the test should not automatically be assumed to require a 30%-50%-80% stepped-load sequence. The testing scope should first be reviewed to determine whether the test is a standalone triennial test or a combined annual and triennial test.
Understanding the difference helps ensure that emergency generators are tested properly, that facilities meet applicable testing requirements, and that customers receive the appropriate scope of work for their specific emergency power system.
If you have questions about your generator’s load bank testing requirements or need help determining which testing approach is appropriate for your facility, contact Weld Power Generator. Our team can help evaluate your emergency power system and develop a testing program based on your equipment, facility load, and applicable requirements.