Abstract: The Detector Module derives a synchronization signal from the half-wave crossovers of the AC power line. A half-wave peak detector detects the peak voltage of each half wave. An impulse detector detects the voltage of any impulses occurring during a half-wave. A common mode detector detects the peak value of each half-wave across the common mode terminals. A microcomputer is provided together with a clock/calendar for recording threshold values and for each half-cycle if a SAG or SURGE is detected; the time that the SAG or SURGE was initiated; the voltage of the half cycle of greatest SAG or SURGE during the event and the number of cycles is recorded. For LO and HI AVERAGE an average resistor stores the average of the peak values for each of the last thirty-two half cycles and that average is compared with the threshold to determine if an event has occurred. If an event has occurred, the duration and the lowest average occurring during the event is stored.