Abstract: The low-voltage power distribution IT system meets the needs of stable and continuous production and operation of giant enterprise equipment. The single-phase grounding voltage optical plate and single-phase grounding current signal indicating device are incomplete in the insulation monitoring function. France and Italy 4Hz AC insulation monitoring device measures the insulation resistance value of the power distribution system and motors under the live operation condition, and also monitors the single-phase grounding fault. In line with IEC-61557 and GB/T 18216, with a complete insulation monitoring function, it is necessary to study the implementation of standards.