Generator Load Tests

Q: What month or year did the load-bank generator testing change from 25% within 30-60 minutes to newer standard 30% at the 30-minute mark? One source stated load-bank test only needed for 1½-hours, now a vendor states it is still a 4-hour load test. Which is correct testing to document?

A: You’re confusing two different load tests. Here is what is required:

Monthly Load Test
The generator must be load-tested once every 20-40 days (i.e. monthly) for 30 minutes. For diesel generators, the load test is required to reach a minimum of 30% of the nameplate rating. For spark-ignited generators (i.e. natural gas), the load is available load. This is a required test.

Annual Load Test
If any of the monthly load tests of a diesel generator fails to reach 30% of the nameplate rating, then an annual load test is required. A load bank must be brought in and the generator operated at 50% nameplate capacity for 30 minutes, then 75% of nameplate capacity for 60 minutes, for a continuous 90-minute load test. This test is only required if any one of the monthly load tests fail to reach 30%. This annual load test is not required for spark-ignited generators.   

3-Year Load Test
Once every 3 years, all generators must be load tested for four (4) continuous hours at a minimum of 30% of the nameplate rating. This test requires the use of available connected load. If the available connected load does not equal 30%, then a load bank is permitted to be used but only as supplemental, not as a primary load.