WL-138 DUOYI 5102A 3 PHASE INSULATION TESTER is an instrument used to measure insulation resistance in electrical systems. This device is especially used when insulation tests need to be carried out in industrial plants, electrical panels and other electrical equipment. The 5102A model is generally designed for use in three-phase systems and can precisely measure insulation resistance. The device is used to ensure the safety of high-voltage power lines and to detect insulation faults.