Power needs for motors, such as those powering well pumps or furnace fans, are more difficult to determine. Electric motors require more current when starting than they do in continuous operation-as much as three to six times more.

Motors are rated by horsepower (hp). A one-horsepower motor requires about one kilowatt to run and a surge of five kilowatts to get started. An electric motor rated for two-horsepower needs twice as much power. So while a motor-powered appliance may run with only one kilowatt, the generator must be able to provide five kilowatts to get it started. Again, those ratings appear on the motor’s face plates. Without sufficient starting power, motors may overheat, burn out or trip the generator’s circuit breaker.