At the distribution transformer, disconnect the fuse on the phase line of the AC contactor that controls the low-voltage line. If the residual current operated protector can be put into operation normally at this time, it proves that the residual current operated protector is good. Otherwise, the residual current operated protector should be repaired and replaced.

At the distribution transformer, disconnect the neutral wire on the outgoing side of the AC contactor that controls the low-voltage line, and then install the removed fuse core on one of the phases. Use a clamp ammeter to measure the phase, and the measured current is the leakage current of that phase. To prevent the presence of phase grounding on the line (such as someone using the one line, one place method to steal electricity, etc.) causing high current damage to the instrument, first place the clamp type ammeter in the high current position during testing; If the detection value is very small, then switch the clamp ammeter gear to milliampere gear for detection.

At the distribution transformer, insert a fuse core into the phase line to be inspected, disconnect the neutral line and the fuses of the other two phases, and use a clamp type ammeter to detect the live phase line on the pole to determine the leakage position. In the case of low voltage line power transmission, clamp type ammeters can also be used to detect low-voltage user connection lines within the suspected range. During detection, the phase and neutral wires of single-phase users should be placed in the jaws of the clamp ammeter at the same time, and the three phase and neutral wires of three-phase users should also be placed in the jaws at the same time. If there is no leakage fault, the clamp ammeter indicates zero, otherwise it is not zero.

Measure the leakage current at the incoming line of the user's power supply using a clamp type ammeter, and at the same time, put the user's electrical equipment and lamps into and out one by one. Check the changes in leakage current by looking at the clamp type ammeter to find the leaking equipment. If all devices are in good condition, or if devices with leakage have exited, but the clamp ammeter shows that the user still has leakage current, it is possible that the user's low-voltage line has leakage, and it should be handled according to the specific situation.

1. When searching for leakage faults, the AC contactor controlling the low-voltage line needs to be forcefully powered on for a short period of time.

2. When searching for leakage faults, attention should be paid to safety, and someone must supervise and take safety measures. When reading clamp ammeter data, it is important to maintain a safe distance between the human body and live parts.

3. High order harmonics may interfere with a few residual current operated protective devices, which may cause them to malfunction. If there are users of large harmonic sources such as intermediate frequency furnaces in the substation area, such users should be removed from operation during detection.

4. This method is particularly effective for finding "one line, one ground" electricity thieves. Its characteristic is that the clamp ammeter displays a large leakage current, reaching several hundred milliamperes to several amperes. For unknown electricity thieves, the above method can be used to search, and for those suspected of such electricity theft, they can be directly checked at their connection line using a clamp ammeter.