Most motors are run continuously with little variation in load. A continuous duty motor is energized and loaded for an extended period of time. When the motor is started, the temperature increases, and then the temperature stabilizes after some time. If the motor was designed with a service factor, it is possible to run the motor at a higher-than-rated load for short periods of time without significant thermal damage to the windings, rotor or bearings. A motor to be used with a continuous load is sized based on that load rating. There are, however, many applications where a motor is not loaded consistently throughout its duty cycle, or is energized intermittently. Some motors are started and stopped often, while others are loaded lightly for some time, then more heavily for some time, and the applied load can vary greatly. If there are periods of time where the motor is operating at less than full load, then it may be possible to size the motor smaller than the maximum load level.
Contrary to popular opinion, bigger is not always better. A case in point is the electric motor, the workhorse of industry. There is a natural tendency to want a little extra power, "just in case." That's why auto makers still sell cars with 300 hp engines, even though the speed limit may be under 70 miles per hour. But, just like those gasguzzlers, operating an oversized electric motor may cost additional money; sometimes, a lot of money. Here is a simple procedure for determining the actual hp required by a load, without expensive equipment or engineering.
Contrariamente a la opinión popular, no siempre, lo más grande es mejor. Un buen ejemplo es el motor eléctrico, el caballo de trabajo de la industria. Existe una tendencia natural a reservar un poco más de potencia, “por si acaso.” Es por esto que la industria automotriz sigue vendiendo vehículos con motores de 300 hp, a pesar que el límite de velocidad está muchas veces por debajo de las 70 millas por hora. Pero así como sucede con estos depredadores de gasolina, el funcionamiento de un motor sobredimensionado puede costarnos dinero extra; algunas veces, una gran suma. Aquí presentamos un procedimiento sencillo para calcular los hp reales requeridos por una carga, sin emplear equipos e ingeniería costosa.