Electrical equipment power ratings are important to consider when wiring, using power supplies or fitting fuses. One confusing aspect of power ratings is the usage of kilowatts (kW) and kVA, both of which express the power of the equipment in a slightly different form. The kVA value will always be higher than the "real" kW value, because in alternating current, the voltage and current are not usually in phase with each other.
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Consult the literature the equipment was provided with to find its power factor. If the electrical specifications are not included in the manual, you may wish to contact the equipment manufacturer and ask them to provide a power factor for the equipment. Failing that, a typical power factor can be used instead (see Resources). These vary depending on the type of equipment and the load it exerts. The power factor associated with different types of motors, for example, can vary from 0.90 down to 0.55, and will be even lower for heavy-duty, high-load motors. Fluorescent lamps typically have a power factor of 0.95 to 0.97.
Calculate the kilowatt value (the "real" power value) by multiplying the kVA (the "apparent" power value) by the power factor. This can be expressed in equation form as follows:
(Real power) = (apparent power) times (power factor)
Verify that your calculation was correct by doing it in reverse. Divide your previous answer by the kVA value and you should get the power factor. In equation form, this is:
(Power factor) = (real power) divided by (apparent power).
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