Generators installed as "Standby" power are designed to operate as back up for the normal utility power source connected to the site. They typically run infrequently for this purpose, and are also run for testing and exercise purposes. The definition is always listed as being for "continuous standby power during the interruption of normal power."  And, by definition, they are designed to operate with varying loads throughout the course of the day, and at their full power rating for no more than 1 hour in any 12 hour period, or 2 hours in any 24 hour period in some literature. There is no overload capability for standby generators.

A generator "prime power" rating also assumes it operates with varying loads, but allows for the generator set to run at its prime power rating a lot of the time, and at 110% of the prime power rating for up to 2 hours in 24 hours.  Specifications frequently call this "10% overload capability." You will notice the prime and standby rating is similar in some respects, neither rating assumes the generator set will run at the stated rating 100% of the time.

A generator's "continuous" rating assumes it will run at that load factor 100% of the time. While not a common rating on smaller systems, larger units fueled with either natural gas or diesel fueled engines, may operate at a "continuous" rating.  Systems that parallel (are connected to) with the utility power grid may operate at a constant base load to ensure heat is produced so it can be captured for other purposes.

You may want to consider coming to one of our training seminars or workshops where we discuss these differences and how all of it relates directly to today's emergency power generators. Take a look here for more information on our classes and dates.