A decrease to between 10 percent and 90 percent of the normal voltage at the power frequency for durations of 0. 5 cycle to 1 minute. (If the voltage drops below 10 percent of the normal voltage, then this is classified as an interruption. ) It is further classified into three categories: (1) Instantaneous — 0. 5 cycle to 30 cycles; (2) Momentary — 30 cycles to 3 seconds; and (3) Temporary — 3 seconds to 1 minute.