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When you see the term "thermal protection" in the description of an electric motor, it refers to a device in the motor or motor compressor.Motor thermal protectorDesigned to prevent dangerous overheating that could cause motor failure.

Purpose of motor thermal protector:

This overheating usually occurs when the motor is overloaded, the bearings seize, the motor shaft locks and prevents it from turning, or the motor fails to start properly. Failure to start can be caused by a faulty start winding in the motor.

A motor thermal protector consists of one or more heat sensing elements built into the motor or motor compressor and an external control device. Thermal protection exists to shut down the motor when too much heat is generated within the motor circuit. This safety feature stops the temperature climb before the motor burns out.

The motor thermal protector will usually reset itself once the motor has cooled to a safe operating temperature. There is usually a visible red button on the wiring side of the motor - usually (but not always) on the opposite side from the motor shaft. On motors equipped this way, you must press this button to reset and restart the motor. On other motors that do not have a reset button, the motor will reset automatically as it cools.

Having a motor shut down because a thermal limiter tripped is inconvenient, but it is certainly better than having to replace the motor because it overheated. A shutdown can alert you to a problem with the motor or the connected equipment, or load connected to the motor. When a motor fails to start or overheats during operation, it may be a sign that the motor has reached the end of its useful life and must be replaced. But often the fault is not with the motor at all. For example, the load connected to the motor may have an obstruction that is causing too much load, which in turn causes heat to build up in the motor.

bringThermal protector for motorExample

Sump pumps are one motor where this often happens. If a sump pump is delivering debris-laden water, the debris can get stuck in the impeller and lock the pump motor's rotation, causing it to overheat very quickly. On pumps equipped with a motor thermal protector, the device will trip and shut off the current to the motor windings. This will allow the motor to cool down and may save it from total failure. Since the motor shuts down to alert you to the problem, you can clean out the impeller and keep the sump pump motor running for a while before it needs to be replaced.

What are motor windings?

The motor windings are the wires within the motor that carry the current. The windings are placed in coils, usually wrapped around a ferromagnetic core, which form magnetic poles when current is energized through them.

The same thing can happen to other motors that handle variable loads, such as garbage disposals, washing machines, or vacuum cleaners. Without thermal protection, such motors are more likely to burn out.

Thermal protection is often a nice feature to have when buying equipment with electric motors. By protecting the motor from overheating, it can greatly extend the life of the motor.