Combined load tests on generators

Q: The AHJs who inspect my hospital require that I conduct a three-year, four-hour load test, which we do simultaneously with our annual load bank test. One AHJ says this is acceptable while another AHJ doesn’t like it and says the annual load test is required to be conducted at varying loads of 25%, 50%, and 75%, and the three-year test is required to be conducted at 30% load. Which one is correct, and where do I find the standards for this testing requirement?

A: Both The Joint Commission and CMS require the three-year, four-hour generator load test, which was introduced in the 2005 edition of NFPA 110, Emergency and Standby Power Systems. This test was further explained in the following 2010 edition of the same NFPA 110 standard. Section 8.4.9 of NFPA 110 requires the three-year test to be conducted at 30% of the nameplate rating of the generator for four continuous hours. The annual load test is only required when the monthly load tests cannot meet the 30% nameplate rating capacity. The annual load test is required to operate the generator at 25% capacity for 30 minutes, 50% capacity for 30 minutes and 75% capacity for 60 minutes for 2 continuous hours. If you combined these two load tests, then the one AHJ is correct; 25% capacity is not equal to 30% capacity for the first 30 minutes of the load test, and that AHJ would be correct for refusing to accept this combined test as evidence of meeting the three-year, four-hour load test. An easy solution to this would be to operate the first 30 minutes of the combined test at 30% capacity, as the load values given are minimum values and may be exceeded.