Which USB line has a 220V casing? USB has 4 lines. In normal state, the two on the side are 5V power supply and the two in the middle are signal lines. The casing is the bottom line and is directly connected to the chassis. Generally, it is normal to have about 100V. This is caused by the power supply. The live wire of the safety capacitor in the power supply is connected to the ground wire, and the neutral wire is also connected to the ground wire. If your 3-phase plug-in board is connected to a ground wire, it won't work. If you don't pick it up, wear slippers or shoes with poor insulation, which will feel numb to the touch. If it's not the shell, you've got a big problem. You can use elimination to find out whose problem it is. Simply put, it's either the monitor or the power supply.