Standby power generators are most often used in emergency situations, such as during a power outage.  It is ideal for applications that have another reliable continuous power source like utility power.  It’s recommend usage is most often only for the duration of a power outage and regular testing and maintenance. Prime power ratings can be defined as having an “unlimited run time”, or essentially a generator that will be used as a primary power source and not just for standby or backup power.  A prime power rated generator can supply power in a situation where there is no utility source, as is often the case in industrial applications like mining or oil & gas operations located in remote areas where the grid is not accessible.    Continuous power is similar to prime power but has a base load rating.   It can supply power continuously to a constant load, but does not have the ability to handle overload conditions or work as well with variable loads.  The main difference between a prime and continuous rating is that prime power gensets are set to have maximum power available at a variable load for an unlimited number of hours, and they generally include a 10% or so overload capability for short durations.