What is Crest Factor

What is Crest Factor

Crest factor is the ratio between the peak value and the root mean square (RMS) value of a current or voltage signal. It is a measurement instrument specification that describes the size of the dynamic range of a waveform or signal. Crest Factor is used to indicate the quality of an input signal and can be a measure of the peak-to-RMS ratio.

In the lighting industry, different types of loads exhibit different current waveforms, which can have varying crest factors. Resistive loads, such as heaters and incandescent lights, have nearly sinusoidal current waveforms with a crest factor near 1.4. Power factor corrected loads, like electronic lighting ballasts and computer power supplies, typically have crest factors ranging from 1.4 to 1.5. Nonlinear loads, such as battery chargers and VSD motor controls, can have crest factors ranging from 2.0 to 3.0 or even higher.

The crest factor becomes particularly important when measuring individual loads with high current crest factors. If the peak current exceeds the capacity of the measuring instrument, such as a current transformer (CT), the readings can become inaccurate. Therefore, it is crucial to select a CT with a rated current that can handle the expected peak current.