AC contactor is generally classified into class I, class II, class III and class IV according to the type of load, and they are respectively recorded as AC-1, AC-2, AC-3 and AC-4. AC-1 AC contactor corresponds to non inductive or micro inductive load as its control object, such as the filament lamp, resistor furnace. AC-2 AC contactor is used for starting and stopping of wound asynchronous motor. Typical application of AC-3 AC contactor is the operation of squirrel-cage asynchronous motor and the break in operation. AC-4 AC contactor is used for starting, reverse braking, reversing and jog of cage asynchronous motor. All ATO AC contactors with 24V/110V/220V coil operating at AC-3 380V or 660V.