When the insulation of the motor stator winding is poor, the insulation is aging, or the stator winding collides with the motor shell, the shell is charged, and the motor shell has a high voltage to the ground. If the motor has no grounding wire, when people touch the motor shell, strong current flows into the earth through the human body, which will cause personal injury and death accidents.
If the motor shell is connected with a ground wire, because the resistance of the ground wire is very small, the potential of the motor shell is equal to the earth, and people will not get an electric shock when touching the motor shell. In fact, when the electric leakage of the motor is serious, such as the stator winding collides with the shell, due to the grounding through the ground wire, resulting in a high short-circuit current, the relay protection device of the motor acts, or the fuse blows, cutting off the power supply, so that the motor stops. Other electrical equipment shells also need grounding wires, and the reason is the same. Therefore, in order to ensure personal safety, the motor is not allowed to operate without grounding wire.
