What is the Required Code to Complete Load Bank Testing?

The Short Answer: Load bank testing makes sure that generators can handle their full electrical load during an emergency. It is important to follow codes like NFPA 110 and NFPA 99, which outline the testing frequency, duration, and specific requirements for generator load bank testing. Regular testing helps prevent issues like wet stacking and ensures your generator is ready when needed most.

For contractors and building engineers responsible for maintaining commercial generators, load bank testing is a crucial task to ensure reliable operation when the generator is needed most. However, conducting load bank testing properly requires adherence to specific codes and standards to guarantee safety, performance, and compliance. In this blog, we’ll cover the essential industry standards and codes you need to follow for generator load bank testing.

What is Load Bank Testing?

Load bank testing simulates the electrical load a generator will face during a real emergency. By applying an artificial load, contractors and engineers can verify that the standby generator is capable of producing the power it’s rated for when called upon.

This type of testing helps detect potential issues like wet stacking and ensures all components, including the exhaust system and prime mover, are functioning correctly under stress, providing peace of mind that the generator will perform when it matters most.

 

The Codes and Standards for Load Bank Testing

Following the right codes and standards is essential for compliance and reliable generator performance. The two primary standards you’ll work with are NFPA 110, which governs emergency and standby power systems for most commercial and critical facilities, and NFPA 99, which sets testing requirements for generators in healthcare environments. Together, they establish the testing frequency, duration, and load conditions your generator must meet.

In addition to these national standards, local jurisdictions may have specific requirements that go beyond NFPA 110 and NFPA 99. Always check with your local Authority Having Jurisdiction (AHJ) to ensure full compliance with local building codes.

 

NFPA 110: Standard for Emergency and Standby Power Systems

NFPA 110 is the primary code governing load bank testing for emergency power systems. It outlines testing frequency, processes, and criteria for various components of standby generators. Some key requirements from NFPA 110:

• Testing Frequency: NFPA 110 requires monthly 30-minute testing using building load or a load bank. If the generator does not reach 30% of nameplate kW during monthly testing, an annual 1.5-hour load bank test is required (30 min at not less than 50%, 1 hour at not less than 75%). Additionally, Level 1 Emergency Power Supply Systems (EPSS), which include critical systems like hospitals and data centers, must undergo full load bank testing at least once every 36 months.
• Duration of Testing: NFPA 110 specifies different durations depending on the type of test being performed.

• Acceptance testing (after new installation): A 2-hour test. It is common practice to apply the load gradually, but not required:
  • 30% load for the first 30 minutes
  • 50% load for the next 30 minutes
  • 100% load for the final hour
• Annual supplemental load testing: A 1.5-hour continuous load bank test:
  • 30 minutes at no less than 50% load
  • 1 hour at no less than 75% load
• Note: NFPA 99 aligns with NFPA 110 requirements unless otherwise directed by the AHJ. 

• Simulating Actual Loads: The test must simulate the real electrical load the generator will handle. If facility loads are insufficient, a portable load bank can be used.

NFPA 99: Healthcare Facilities

For contractors working in healthcare settings, NFPA 99 governs the testing of electrical systems, including load bank testing in hospitals and other healthcare facilities. Some NFPA 99 load bank testing details are: 

• Annual Testing: Healthcare generators follow the same conditional annual testing requirement as NFPA 110, undergoing a 1.5-hour load bank test if monthly testing does not reach 30% of nameplate kW.
• 90-Minute Test: Like NFPA 110, NFPA 99 requires a continuous 90-minute test consisting of 30 minutes at no less than 50% load and 1 hour at no less than 75% load.

Load Bank Testing and Load Types

When conducting load bank testing, different types of load banks are used depending on the generator’s intended use and the load conditions it will face. The two main types are resistive load banks and reactive load banks. It’s also important to understand the difference between the artificial load applied during testing and the actual electrical load the generator may face during a power failure.

Resistive Load Bank

• Simulates real power: A resistive load bank uses resistive elements (like heaters) to directly simulate the electrical load that the generator will handle in everyday operations.
• Used for testing: It’s the most common type of load bank used for testing, as it mimics the typical electrical demand of most buildings and facilities.

Reactive Load Bank

• Simulates reactive loads: A reactive load bank is used to simulate loads found in systems with inductive elements like motors. It introduces a magnetic field to create a reactive load, helping test the generator’s ability to support such systems.
• Used for specialized testing: These are especially useful for testing generators that power equipment like air conditioning systems or large motors, which require a reactive element.

Artificial Load

• Simulated load: An artificial load is created by electronic load banks or resistive/reactive elements. These are used when the facility’s real load is insufficient for testing.

Electrical Load

• Real-world demand: Electrical load refers to the actual power demand placed on a generator during an emergency. It includes systems like lighting, cooling, and computers, which require constant and reliable power.

Why Regular Load Bank Testing Matters

Regular load bank testing is essential for ensuring that your generator remains reliable and performs effectively under real-world conditions. This routine testing helps prevent major issues that can compromise a generator’s performance when it’s needed most.

• Preventing Wet Stacking
  • Wet stacking occurs when a generator runs at low loads for extended periods, causing unburned fuel to accumulate in the engine. This issue is especially common in diesel generators that are underused. Load bank testing forces the generator to run at full capacity, which prevents wet stacking and ensures the engine operates at optimal temperatures.
• Ensuring Generator Performance
  • Regular load testing ensures that your emergency generator can meet its output capacity when it’s called into action. It checks the generator’s ability to handle electrical energy demands and ensures it can provide the necessary backup power. Without this testing, you risk not knowing whether your generator will fail during an emergency.
• Test All Systems & Components
  • During load bank testing, all systems and components of the generator are put to the test to ensure they perform properly under full load. This includes checking the exhaust system, fuel delivery, cooling systems, and electrical components. Each part of the generator must operate effectively to ensure reliable performance during a power failure.

What Happens During a Load Bank Test?

A load bank test simulates the real-world electrical load a generator will face in an emergency, helping engineers verify it can meet power demands and operate at full capacity.

A portable load bank is connected to the generator and applies a controlled, incremental electrical load to verify performance under operating conditions. Outside of NFPA acceptance testing, routine field tests can run around 2 hours and up to approximately 80% load to adequately exercise the system, with load levels and duration adjusted as required.

Throughout the test, technicians monitor key engine and electrical parameters such as voltage, frequency, load (kW), oil pressure, coolant temperature, and exhaust temperature to assess performance and identify potential issues. Afterward, the collected data is analyzed to confirm that the generator meets its nameplate kW rating and is operating within specifications under load conditions.

 

Ensure Your Generator is Ready

Complying with NFPA 110, NFPA 99, and local building codes is essential for contractors and engineers responsible for load bank testing. Regular load tests ensure that emergency power generators are ready to perform when needed most. By adhering to these industry standards, you help prevent issues like wet stacking, maintain generator performance, and ensure reliable power for critical systems.

At Duthie Power, our expert technicians are ready to help you meet compliance standards and provide reliable backup power when you need it. For more information on generator load bank testing requirements, request a quote or give us a call at 1-800-899-3931.