Exercising a diesel generator without load can promote “wet stacking”; however, not exercising the diesel promotes more problems than not exercising at all.
The purpose of monthly testing is to verify that the EPSS is capable of supplying service to all emergency and equipment systems, within the prescribed time period after a power outage, and for the duration specified by the authority having jurisdiction. Most facilities perform the weekly inspection before the monthly load test because the temperature of the engine and fluids is cooler.
For starters let’s clarify three simple, but often misunderstood points about the paragraph below.
- Notice the paragraph states that an inspection only, not an exercise, shall be made on a weekly basis.
- This paragraph pertains to two activities – inspecting and testing the EPSS – activities which involve all its components, with the generator, or EPS, representing but one.
- Some inspectors believe a generator needs to run, with or without load, to be “inspected.” This is not true.
NFPA 110, 8.4.1* EPSSs, including all appurtenant components, shall be inspected weekly and exercised under load at least monthly.
NFPA 110, A.8.4.1 See Figure A.8.4.1(a) and Figure A.8.4.1(b).
Also, exercising a diesel without load can promote “wet stacking”; however, not exercising the diesel promotes more problems than not exercising at all. The other components of the EPSS, including the automatic transfer switches, day tanks, etc., must be inspected each week as well as exercised monthly.