Small current grounding line selection device now has a certain reliability, but in the small current grounding system, power users are prone to single-phase grounding fault probability is high, line selection device is not accurate, operators can not quickly and accurately remove the fault line, it will damage the safe operation of the system.

In the small current grounding system, the main reason for the low accuracy of the small current grounding line selection device in the power supply system is probably that the connection of the grounding wire during the construction and installation of the cable head does not meet the requirements. Before installation, there must be a special person responsible for on-site follow-up to eliminate the inaccurate factors of the device due to incorrect wiring, otherwise the equipment can not be checked during operation, and it will be very troublesome for important users to check the power failure.

In the code for construction and acceptance of grounding device in electrical equipment installation engineering, it is required that the grounding wire should pass through the zero sequence current transformer. When the grounding point (the welding point between the cable grounding wire and the cable metal shield) is above the transformer, the grounding wire should pass through the transformer reversely before grounding. When the cable grounding point is below the transformer, the grounding wire should be directly grounded. Other installation methods are typical wrong positions, which will cause the zero sequence current can not be collected in case of grounding fault, so the line selection device can not operate correctly. In addition, it is strictly forbidden to contact the grounding line selection with the fixing clip.

The correct installation of zero sequence current transformer is related to the line selection accuracy of small current grounding line selection device. If the zero sequence current transformer has been installed, it needs to be checked one by one, carefully check the ground connection mode, and adjust the incorrect one.