When the insulation of the motor stator winding is poor, the insulation is aging or the stator winding collides with the extruded aluminum motor housing, the shell is charged and the extruded aluminum motor housing has a high voltage to the ground. If there is no grounding wire for the motor, when people touch the extruded aluminum motor housing, strong current flows into the ground through the human body, which will cause personal injury and death.
If the motor case is grounded with a ground wire, because the resistance of the ground wire is very small, the potential of the motor case is equal to that of the ground, and people will not get electric shock when contacting the motor case. In fact, when the motor leakage is serious, such as when the stator winding collides with the shell, a high short-circuit current is caused due to grounding through the ground wire, the relay protection device of the motor acts, or the fuse is blown, the power is cut off, so that the motor stops. The case of other electrical equipment also needs grounding wire, the principle is the same. Therefore, in order to ensure personal safety, the motor is not allowed to run without grounding wire.
