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How does the motor thermal protector prevent dangerous overheating of the motor?
 Jul 19, 2021|View:92

When you see the term "thermal protection" or "thermal protection" used to describe an electric motor, it refers to a device within an electric motor or motor compressor designed to prevent dangerous overheating that could cause the motor to fail, called amotor thermal protector.


Use of motor thermal protector

This overheating usually occurs when the motor is overloaded, the bearings get stuck, something locks the motor shaft and prevents it from turning, or the motor fails to start properly. Failure of motor starting winding may result in failure of starting.


The motor thermal protectorconsists of one or more heat sensing elements built in the motor or motor compressor and external control devices. Thermal protection shuts down the motor when too much heat is generated in the motor circuit. This safety feature stops when the temperature rises and then burns out the motor.

motor thermal protector

Once the motor has cooled to a safe operating temperature, the motor thermal protector will usually reset itself. There is usually a visible red button on the wiring side of the motor, which is usually, though not always, located opposite the motor shaft. On a motor mounted in this manner, this button must be pressed to reset and restart the motor. On other motors that do not have a reset button, the reset occurs automatically as the motor cools.


It is inconvenient to shut down the motor because the thermal limit trips, but it is certainly better than overheating and having to replace the motor. Also, a shutdown can alert you that there is a problem with the motor or connected equipment, or that there is a problem with the load on the motor. When the motor fails to start or overheats during operation, it may indicate that the motor has reached its service life and must be replaced. But usually the fault is not in the motor at all. For example, the load attached to the motor may have obstacles that cause the load to be too large and cause heat to build up within the motor.


Motor thermal protectors are usually a good feature when buying equipment with a motor. By preventing the motor from overheating, the service life of the motor can be greatly extended.