NFPA 110, 18.104.22.168* states: “Diesel-powered EPS installations that do not meet the requirements of 8.4.2 shall be exercised monthly with the available EPSS load and shall be exercised annually with supplemental loads at not less than 50 percent of the EPS nameplate kW rating for 30 continuous minutes and at not less than 75 percent of the EPS nameplate kW rating for 1 continuous hour for a total test duration of not less than 1.5 continuous hours.”
Question #1: What is the reasoning behind the 30-minute requirement at not less than 50% of the nameplate kW rating?
Answer #1: During an annual load bank test, you might not want to hit the engine with a “block load” to which the engine may not be accustomed, which could damage the engine. The only “compliance reason” you would be performing the load bank exercise is if the engine was less than 30% loaded during the monthly tests.
Question #2: If the load bank test shows not less than 75% for a full 1 hour and 30 minutes, are we in compliance?
Answer #2: Yes, 50% and 75% are minimums.
Question #3: If the minimum exhaust gas temperature requirement is to prevent wet stacking, then why is it acceptable for the monthly test to be conducted at a 31% load when our exhaust gas temperature is still well below the minimum set by the manufacturer?
Answer #3: A comparison should be made between the actual measured temperature at a 30% load, and the manufacturer’s guidelines for exhaust temperatures at a 30% load, not 100%. This information is available from the factory. Chances are you will be right on the money.