Electric chain hoist is a kind of handling equipment used to lift and carry heavy objects and make them move up and down horizontally and vertically within a short distance. It is an indispensable lifting and handling equipment in the production process. The main body of the electric chain hoist is hung on a traveling trolley, and the trolley travels along the I-beam of the crane beam for in-position operation.

During the operation of the electric chain hoist, if the long-term load is too large, the operation is frequent, or the short-phase operation, etc., the electric current of the electric hoist motor may exceed the rated value. Sometimes the leakage circuit breaker will not trip in this case, which will eventually cause the motor windings to overheat, the temperature exceeds the allowable temperature rise, damage the insulation, affect the service life of the electric chain hoist, and even burn the motor. The electric chain hoist needs to be protected against overload.

The most commonly used electric chain hoist overload protection device is the use of thermal relays. The heating elements of the thermal relays are connected in series in the two-phase main circuit of the control circuit. The normally closed contacts are installed in the control circuit. When the current exceeds the rated value due to overload or other reasons After a period of time, the heating element is heated and bent, and the normally closed contact connected in series in the control circuit is disconnected. The control circuit is cut off, the coil of the contactor is de-energized, the main contact is disconnected, and the motor is separated from the power supply and stops. To the role of overload protection.