Real Power - Real power is the actual power being used in a circuit.

Apparent Power - Apparent power is the power calculated for that circuit based upon measuring only volts and amps with a volt-ammeter.

To understand power factor, you need to know that: The power (watts) available in an alternating current (AC) circuit is equal to volts times amps. A volt-ammeter measures the voltage and the amperage in an AC circuit.

If the voltage and amperage in a circuit peak at the same instant, they are said to be in sync and the power factor (PF) is 1.00. This means that the real power and apparent power are the same.

However, in electrical circuits with coils (such as induction motors, solenoids, and transformers) inductive reactance causes amperage to lag behind voltage. They are out of sync.

If the volts and amps do not reach their maximum at the same instant, the available power (volts x amps) is less than the measured power. This is because the volt-ammeter measures the mean value of volts and of amps and does not show whether they peak at the same instant.

Thus, the real power (the available power) is less than the apparent power (the measured power) and the power factor is less than 1.00.

Adapted from Basic Electricity, LAMA Books.

Publication date: 06/06/2005