AC load is generally divided into one, two, three and four categories, which are respectively recorded as AC1, ac2, AC3 and Ac4. One kind of corresponding control object is non inductive or micro inductive load, such as incandescent lamp, resistance furnace, etc.; the second kind of AC contactor is used for starting and stopping of wound asynchronous motor; the typical use of the third kind of AC contactor is squirrel cage type operation and breaking in operation; the fourth kind of AC contactor is used for starting, reverse braking, reverse and inching of cage type asynchronous motor.