1. Check the DC cables and grounding of the components First, the reason for abnormal insulation impedance is that the DC cables are damaged, including cables between components, cables between components and inverters, especially cables in corners and cables laid outdoors without pipes. All cables need to be carefully checked for damage. Secondly, the photovoltaic system is not well grounded, including the grounding holes of the components are not connected, the component blocks and the brackets are not in good contact, and some branch cable sleeves are flooded, which will lead to low insulation impedance.   2. Rely on the inverter to check string by string If the DC side of the inverter is multi-channel access, the components can be checked one by one. Only one string of components is retained on the DC side of the inverter. After the inverter is turned on, check whether it continues to report errors. If it does not continue to report errors, it means that the insulation performance of the connected components is good. If it continues to report errors, it means that it is very likely that the insulation of the string of components does not meet the requirements. For example, if the Growatt MAC 60KTL3-X LV inverter is connected to an 8-way string and one of the strings is unplugged, if the fault alarm disappears, it means that the string is faulty.   3. When using a megohmmeter or other professional equipment to detect each string on site, use a megohmmeter to measure the insulation resistance of the PV+/PV- to the ground on the component side string by string. The impedance needs to be greater than the threshold requirement of the inverter insulation impedance. In some projects, dedicated insulation measurement equipment can also be used.