Electrical ac contactor is a kind of intermediate control element. It has the advantage of frequent switching on and off, and controlling high current with small current. With the thermal relay work, but also to the load equipment to play a role in overload protection. Because it is on the electromagnetic suction switch on and off work, compared with the manual opening and closing circuit, contactors is more efficient, more flexible use, can simultaneously, multiple load circuit, and short circuit self-locking function, through manual pull, can enter the self-locking state continuous work.

Electrical ac contactor is the most common low voltage control appliance used in electric drive and automatic control system. As an actuating element, it is used for switching on, breaking off lines, or frequently controlling the movement of motors and other equipment. Electrical ac contactor consists of movable and static main contacts, arc extinguishing cover, dynamic and static iron core, auxiliary contact and support shell. When the electromagnetic coil is electrified, the movable iron core is attracted by the electromagnetic force, and the movable contact is contacted with the static contact directly or through a lever to switch on the circuit. When the electromagnetic coil is powered off, the movable iron core is automatically returned under the action of a reset spring, which is commonly called release, and the contact is separated and the circuit is broken.

More than 90% of automation control power systems are using contactors, which shows how wide it is used.