What Is the difference between Horsepower and Kilowatts?
AC motors manufactured in the United States are generally
rated in horsepower, but motors manufactured in many other
countries are generally rated in kilowatts (kW). Fortunately it is
easy to convert between these units.
power in kW = 0.746 x power in HP
For example, a a motor rated for 25 HP motor is equivalent to a
motor rated for 18 .65 kW.
0.746 x 25 HP = 18 .65 kW
Kilowatts can be converted to horsepower with the following
formula.
power in HP = 1.34 x power in kW
What does the Service Factor on a Motor Mean?
Service factor is a number that is multiplied by the rated
horsepower of the motor to determine the horsepower at
which the motor can be operated. Therefore, a motor designed
to operate at or below its nameplate horsepower rating has a
service factor of 1.0.
Some motors are designed for a service factor higher than 1.0,
so that they can, at times, exceed their rated horsepower. For
example, this motor has a service factor of 1.15. A 1.15 service
factor motor can be operated 15% higher than its nameplate
horsepower. Therefore a 30 HP motor can be operated at
34.5 HP. Keep in mind that any motor operating continuously
above its rated horsepower will have a reduced service life.
Starting Current and Full-Load Current:
Starting current, also referred to as locked rotor current, is
the current supplied to the motor when the rated voltage is
initially applied with the rotor at rest. Full-load current is the
current supplied to the motor with the rated voltage, frequency,
and load applied and the rotor up to speed. For a NEMA B
motor, starting current is typically 600-650% of full-load current.
Knowledge of the current requirements for a motor is critical for
the proper application of overcurrent protection devices.
