What is Current Crest Factor

Horace He

Last Updated: August 28, 2023

What is Current Crest Factor

Current crest factor is the ratio between the peak current and the root mean square (RMS) current. It is a measure of the amplitude of the current waveform and plays a crucial role in accurately measuring and monitoring electrical loads.

Different types of loads exhibit different current waveforms, resulting in varying crest factors. Resistive loads, such as heaters and incandescent lights, typically have nearly sinusoidal current waveforms with a crest factor close to 1.4. Power factor corrected loads, like electronic lighting ballasts and computer power supplies, generally have crest factors ranging from 1.4 to 1.5.

However, nonlinear loads, including battery chargers and VSD motor controls, can have significantly higher current crest factors, often ranging from 2.0 to 3.0 or even higher. These loads produce current waveforms with pronounced peaks, which can impact the accuracy of measurements if not properly accounted for.

When metering individual loads with high current crest factors, it is essential to select the appropriate current transformer (CT) rated current. The peak current of a load with a high crest factor can exceed the capacity of the CT inputs, leading to inaccurate readings due to clipping. To ensure accurate measurements, a CT with a higher rated current should be chosen to accommodate the peak current.

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