Abstract: Provided is an apparatus that includes sensors configured to ascertain two or more alternating current voltage signals. In some aspects, a first AC voltage is sensed at a resistor branch and a second AC voltage is sensed at a resistor-capacitor branch. A processor is configured to transform the two alternating current voltage signals into two instantaneous direct current voltage values. Analysis of at least one direct current value is performed to determine whether or not the instantaneous RMS line voltage is within or outside the range of the required (or expected) RMS line voltage. If the direct current value indicates that the line voltage is outside the expected RMS voltage value, it is determined that an alternating current line fault has occurred or is occurring.