The Street Articles

Because of an annoying thing called “power factor”. AC power is an alternating sine wave (or some other repeating wave form that hopefully resembles a sine wave to some degree or another). As a waveform, AC has both a frequency and, critically to this discussion, a phase, which in this case refers to how much the voltage component of the waveform either leads or lags the current component.  Purely resistive loads don’t affect phase: the voltage component remains in sync with the current component. However, reactive loads (those with either net capacitance or net inductance) affect phase, causing the voltage component to either lead (inductive loads) or lag (capacitive loads) the current component of the waveform.  This results in the true power being less than the product of the RMS voltage and the RMS current (which is called “apparent power”), precisely because the two components are out of phase. The difference between true power and apparent power is called “reactive power...