The detection of faults in the outer sheath of buried cables, like the detection of faults in power cables, generally involves two steps: "initial measurement" and "fixed point". The initial measurement (distance measurement) of grounding faults in the outer sheath is generally carried out using voltage drop method and bridge method. Due to the limitations of the bridge method testing, it cannot test for multi-point grounding faults, nor can it test for faults in three-phase cable chain grounding connections. This instrument is designed to address the characteristics of outer sheath faults. It uses the voltage drop method to initially measure the grounding fault of the cable outer sheath, and then uses the step voltage method to locate the fault point. Two grounding rods are used to locate the low point of the soil potential and set the point. The test current flowing into the ground at the fault point causes a transition point between positive and negative voltage peaks. When approaching the fault point, the step voltage increases, and after crossing the fault, the step voltage decreases and the polarity changes. When directly above the ground fault point, the pointer stops at zero position, which is the accurate location of the cable fault point. The instrument is used for detecting faults in the outer sheath of cross-linked cables; It can also be used for detecting faults in buried wires and all plastic wires (cables without metal protective layers); It can also be used as a 10KV DC withstand voltage test for cables or other electrical appliances.