Q: When doing monthly generator testing, do you have to maintain 30% for 30 minutes or does hitting the 30% sometime during the 30 minutes suffice? In other words, if I run for 30 minutes loaded and reach the 30% for 15 of those minutes does the test pass? Thanks in advance. I take care of an Air Force hospital and my understanding is, during the 30 minutes you capture your peak, whether it be for 10 minutes or the whole 30, as long as it reaches 30% sometime during the test. Actually, the Air Force runs for an hour instead of 30 minutes.

A: According to section 8.4.2 of NFPA 110-2010, diesel generators must be exercised at least once monthly for a minimum of 30 minutes using one of the following methods:

1. Loading that maintains the minimum exhaust gas temperatures as recommended by the manufacturer, or
2. Under operating temperature conditions at not less than 30% of the nameplate kW rating.

So, this means once the generator achieves 30% of the nameplate kW rating, then the test begins and continues for at least 30 minutes, and must maintain a minimum of 30% of nameplate kW rating for the length of the 30-minute test.

I would say the way you have been conducting the monthly load test on the generator would not meet the requirements of NFPA 110-2010, section 8.4.2.