Shear type and tooth insert type motor thermal protector because of inconvenient maintenance, easy to break teeth and other reasons can not adapt to the needs of modern industrial development, has been rarely used. Ball type overload protector has been continuously enriched and developed with the development of modern industry. It is the main force of mechanical motor thermal protector in the future.

Step 1: the earliest used is shear motor thermal protector, pin installed in hardened steel sleeve, overload is cut off, once the overload cut torque can not automatically restore the ability to work, its simple structure, easy to manufacture, compact structure but not high accuracy, used for few overload occasions.

Step 2: toothed motor thermal protector, is developed from toothed clutch, safe release torque is pre-set by compression spring, clutch can be reset automatically at rest or low speed. It will produce impact force at the moment of disengagement and may break teeth. It is generally used for shafting with low speed and small rotational inertia of the driven part.

Step 3: friction motor thermal protector, overload due to friction energy consumption to ease the impact, so smooth work, adjustment and easy to use, simple maintenance, high sensitivity, overload elimination that automatic recovery, used for high speed, large moment of inertia of the transmission device, is currently more widely used products.

Step 4: ball type (steel ball type) motor thermal protector, its manufacture is simple, reliable, overload sliding friction torque is small (some almost no), high action sensitivity, high automatic recovery accuracy, its structure form is also the most abundant, is the ideal product of automatic industrial production.