A
voltage sag (U.S. English) or
voltage dip (British English) is a short duration reduction in
rms voltage which can be caused by a
short circuit,
overload or starting of
electric motors. A voltage sag happens when the rms voltage decreases between 10 and 90 percent of nominal voltage for one-half cycle to one minute. Some references defines the duration of a sag for a period of 0.5 cycle to a few seconds, and longer duration of low voltage would be called a "sustained sag".