This compact handheld Phase Sequence Detector can help you quickly and easily verify the wiring on your 3-phase applications. Connect the Detector to any 3-phase circuit with nominal operating voltage from 188 to 660 volts (Wye or Delta with operating frequencies of 50, 60, or 400 Hz) and LEDÕs will indicate phase sequence (ABC or CBA), phases present or missing and 400Hz frequency. A Low Battery lamp is also provided to indicate when the 9V battery needs to be replaced. This unit is engineered and built in the U.S.A. and has a 5-year warranty.