Circuit-breaking protection measures
That is, timely cut off the short-circuit high current in the motor and its running route, because the short-circuit high current will burn the motor in a very short time, and even threaten the normal operation of the entire line and other equipment, resulting in serious consequences. For motors with a voltage less than 500V, fuses or electromagnetic instantaneous releases in circuit breakers are usually used for circuit-breaking protection.

Overload protection
When the motor has a large overload current, the fuse may not be able to melt, so a separate device is required to cut it off. When the motor is overloaded by 20%, the thermal relay will cut off the power supply within 20 minutes, and it is generally protected by a thermal relay or a thermal release.

Phase loss protection
Phase loss protection is also a kind of overload protection. It is difficult for ordinary thermal relays to completely protect the motor. Therefore, if the environment permits, a separate protection device should be set up to protect it. The most commonly used methods are: using a thermal relay with a phase loss protection device for defect protection; using an undercurrent relay to implement phase loss protection; using a zero-sequence voltage relay for phase loss protection; or using a broken wire voltage relay to implement phase loss protection; using a transformer with saturated current for protection.

Protection against loss of voltage and undervoltage
The implementation of loss of voltage and undervoltage protection is mainly to prevent the machine tool motor from starting and running under very low voltage, or the motor suddenly loses power during operation and then suddenly resumes power supply, causing self-starting. The electromagnetic mechanism of the AC contactor, the loss of voltage release of the circuit breaker, or the undervoltage release of the coupled pressure reduction starter play the role of loss of voltage and undervoltage protection. When the actual voltage is lower than the rated voltage in the range of 35% to 70%, the electromagnet will automatically release, and the loss of voltage and release will cut off the power supply.

Grounding protection
When the motor casing is charged, in order to prevent workers from getting electric shock, a corresponding protection mechanism needs to be adopted to reduce the harm to the equipment and workers.