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      Generator Testing

      by Bob Armbrister, on Dec 4, 2019 12:00:00 AM

      Q: We have a generator that doesn’t meet the 30% load for the monthly run so we have to do an annual run with the load at 50% for 30 min and 75% for 60 min for a 90-minute continuous run. Our contractor did the annual run but he ran it with 52% for 30 min, 75% for 30 min and 81% for 30 min, then he continued to run it for 2½ more hours dropping the percentages as he went for 4 continuous hours at not less than 30%. My question is does these meet the intent of the standards for both an annual and a 3-year load test?

       A: According to section of NFPA 110-2010, when the 3-year load test is combined with the annual load test, the first three hours shall be not less than 30-percent of the nameplate kW rating, and the remaining hour shall be not less than 75-percent of the nameplate kW rating.

      I would say the test as you described could meet both the annual requirements and the 3-year test requirements, depending on how the test was administered. It is obvious that an external load bank would be required for the annual test since the building load did not meet the minimum 30%.

      But section of NFPA 110-2010 requires the 3-year test to begin with the building's load through the ATS and only supplement the load with a load bank if the load cannot meet 30%. It is not at all that easy to combine an annual load test with a 3-year load test, because the 30% minimum load is not achieved through the building's load.

      The generator load testing requirements are minimum load settings, and it is permitted to exceed these minimums.

      Topics: Testing (Generators) Automatic Transfer Switches Inspection & Maintenance (Generators)

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