The contactor is a device assembly, whose contacts are closed by an electromagnet and maintained in such a state, while the coil voltage is not high enough. After stopping the coil circuit occurs the armature drop (by spring) and working the contact opens. 
Principle of operation
Design and operation of contactors almost entirely correspond to the electromagnetic relay. The difference is, contactors that are used to connect the main circuit (eg, engine), and the electromagnetic relays are designed for the connection of auxiliary circuits (eg, alarm). Contactors, in addition to the main contacts can have multiple auxiliary, used for signaling and blocking. The principle of operation of the contactor explains the following schedule:
Under the action of the current, S flowing through the contactor coil creates a force of attraction Anchor K, which leads to the closure of the main contacts Z1, Z2, Z3 and auxiliary z1, z2.
Basically, contactors are designed for the remote connection of three-phase alternating current circuits. They can also be used to connect motors and heaters.
Basic elements of the contactor
Any contactor It has a number of essential elements:
- an electromagnetic core,
- coil,
- insulating base,
- a spring bias,
- make contacts,
- interrupters.
Some contactors may be bimetallic relay, that protect them from overload.
Other types of contactors
In addition to the AC contactor exist DC contactors. They have an electromagnetic or pneumatic actuator, where both solenoid valves are controlled or constant current. They are mainly intended for railway transport, trams and batteries (in trucks).
Contactors for AC coils available in the power range from 1,5 to 238 KB, DC output range is from 2,2 to 11 kW. The apparatus may include multiple auxiliary relay. If necessary,, they can replace the thermal relay for motor protection.
Применение контакторов
Based on this, contactors can be used to pump, engines, engines, fan, lamps, heaters, alarms, and many other electrical appliances.
