Magnetic contactor is not a protection device. It does not protect a circuit under any circumstances like the circuit breaker does. The purpose of magnetic contactor in a circuit is switching. This switching might associated with high power handling, frequent operations etc. With magnetic contactor we can operate motor of any rating from a distance. There are magnetic contactor of kilo ampere range in the market.
Magnetic contactor is different from relay and circuit breaker:
Magnetic contactor is a switchgear device like a relay but it has the higher current capacity and hence has some extra use in power circuits. Where relay can be operated by below 1 amp, magnetic contactor may be used in over 1KA power circuits. It is made for frequent switching operation even might be switched on & off 1000 times in a day. Hence it is mechanically robust and strong to withstand such switching and capable of handling high power.
Magnetic contactor is the robust version of relay. Relay handles small power for its weak contacts, but magnetic contactor can handle high power. So this protection device can be used in power circuit. A magnetic contactor can not actuate or operate by itself it always needed an external signal like relay. On the other hand Circuit breaker is not made for frequent operation, but it can operate or actuate by itself or send some signal to external circuit.
Construction of magnetic contactor:
Magnetic contactor has three parts. 1.power coil, 2.Auxiliary coil, 3.Spring mechanism. The power coil carry high current and auxiliary contactor receives signal to make the contactor open or close or send the status of the contactor(on or off) to external systems like PLC, SCDA. The spring mechanism provides mechanical force to make the contact on or off.
Enclosures are made of insulating materials like Bakelite, Nylon 6, and thermosetting plastics to protect and insulate the contacts and to provide some measure of protection against personnel touching the contacts.