You've raised a few key points, and the answer is nuanced and depends on how strictly your AHJ interprets and enforces NFPA 110. Let's break it down

Understanding NFPA 110 and Load Bank Testing
NFPA 110 8.4.2 (Load Bank Testing)

This section primarily focuses on generator performance under load. It mandates periodic testing (typically annually) at a percentage of the generator's nameplate kW rating. The goal is to ensure the generator can deliver its rated power and maintain voltage and frequency stability. You are correct that 30% is a common minimum target.

ATS Testing

NFPA 110 does require regular testing of automatic transfer switches, but not necessarily under a full load bank condition.

Rotational Tests (NFPA 110)

You are right; Monthly testing of the ATS is generally required. Usually, this testing simply involves simulating a power loss and observing the ATS transfer to the generator. It confirms that the ATS functions correctly and transfers to the generator upon a simulated power failure. This can often be done without a load bank.

Addressing Your Questions1. Docking Station Size & 30% Load Bank for Both Generators

Yes, your approach of sizing the docking station to handle at least 30% of the combined capacity of both generators is a reasonable interpretation of NFPA 110 8.4.2 when they are operating in parallel. You treat the paralleled system as a single larger unit for this load bank test.

Important Caveat

Check with your AHJ. Some might insist on testing each generator individually at a specified percentage of its rating, even if they are designed to operate primarily in parallel. This is the most conservative interpretation and would require a larger docking station or the ability to switch the load bank between generators.2.

Required testing of separate ATS branches? Not usually during the NFPA 110 8.4.2 generator load bank test

The primary purpose of the generator load bank test is to verify the generator's performance. While the ATSs will be operating during this test (transferring the load to the generator), you are not specifically testing the ATSs under load as the primary objective.

The key thing to clarify with your AHJ is whether or not the AHJ views the load bank test as serving a dual purpose. If it does, then this will likely involve setting up each ATS branch and making sure each branch is properly exercised as well. This is not uncommon, especially in facilities dealing with health care and the need for very reliable generator performance. If the AHJ wants to ensure each ATS can carry at least the legally required load, then you'll have to test each branch individually.3. Load Banking Each Branch Separately? Typically Not Required (But Check with AHJ)

In most scenarios, separately load banking each ATS branch to verify the ATS capacity is not a typical requirement of NFPA 110, provided that the generator load bank test provides a sufficient load across the whole system. The generator testing is usually designed to verify the generators' output. The ATS test is designed to ensure the ATS switches on a failure and stays in position and that it's connections are firm.4.

Generator-Only Testing vs. ATS Testing You're on the right track. The generator load bank testing and ATS rotational testing are distinct activities. The docking station is primarily for the generator load bank test. The monthly ATS tests are generally low-load/no-load operational tests.

Recommendations and Considerations1. Consult with Your AHJ (Authority Having Jurisdiction)

This is crucial. Clarify their expectations for load bank testing and ATS testing in parallel generator systems. Ask them specifically: Do they require individual generator testing even with a parallel system? Do they require ATS verification under load as part of the NFPA 110.2.

Comprehensive Testing Plan

Develop a written testing plan that clearly outlines: Generator load bank test procedure (including the percentage of rated kW, test duration, and parameters to be monitored – voltage, frequency, etc.) ATS testing procedure (including the method for simulating power failure, the expected transfer time, and verification of transfer).3.

Future Scalability

Consider if your load requirements are likely to increase in the future. Oversizing the docking station a bit now could save money later.4.

Docking Station Features

Look for docking stations with features like: Metering to accurately measure kW, voltage, and frequency. Load control (manual or automatic) to adjust the load during the test. Safety interlocks to prevent accidental overloads or incorrect connections.5.

ATS Inspection and Maintenance

Don't neglect regular inspection and maintenance of your ATSs. Check for loose connections, signs of overheating, and proper operation of the transfer mechanism.

In summary: Plan for a docking station that can load bank at least 30% of the combined capacity of your parallel generators. However, always* confirm your approach with your AHJ to ensure compliance. The generator load bank test is primarily for verifying generator performance, while separate ATS testing is typically a low-load or no-load operational check. Your AHJ will define whether the load bank test serves as a dual check for both generators and ATS's. Remember to develop a comprehensive testing plan and maintain your equipment properly. Flag for review