Loading of a diesel generator

Depends on the size and speed. Get a fuel consumption curve to find best economy, and you be surprised that it might be lower load or speed than you expect. For engine 'health' do not go lower than 25% or above 100% of the "continuous 24/7 uninterrupted" rating. Too low and there isn't enough heat to keep things happy (too complex to explain in a quick post) and rings will not seat and blow by will go up. The key to maximum rating is the definitions the supplier has. Get a perfect definition for ratings. 'Standby' is normally 20% above continuous, Prime means you can overload it 10% for a hour and is normally 10% above continuous. Suppliers have different definitions, but all will tell you. And watch how confusing the rating definitions will be. Low load kills chemically; hi load kills thermally and mechanically.

In addition to "PetroPower"'s explanation, please consider the block loading characteristics of the engine and generator....too much instantaneous load will drag the engine RPM's down and reduce generator Hertz, tripping the output breaker if lower than your paralleling gear setpoint. My experience was recent during commissioning of new UPS units....engineer required block loading of UPS on bypass in addition to UPS on-line where the UPS would step in the load. Interesting.....