Magnetic Contactor

Magnetic Contactor Points :Definition of Magnetic Contactor An electro-magnetic device that repeatedly establishes or interrupts an electrical power circuit Contactors are required in automatic controls to transmit varying conditions in one circuit to influence of operation of other devices in the same or another electrical circuit.

A contactor is a simplified form of circuit breaker that is designed for frequent operation in the normal closing and opening of circuits under load. Contactor has a coil, which can be energized to close or open contacts in an electrical circuit. The contacts of the magnetic contactor are closed against the opposition of the spring by the magnetic pull exerted on the armature by the iron-cored operating coil. The contactor consists of a number of contacts such as main contacts and auxiliary contacts, spring, electro magnet, armature and casing. The coil and contacts of a contactor are represented by symbols on the circuit diagram, which are labeled on the contactor.

The coil is energized by separate control circuit that goes back to a push button. The coil is energized with AC or D.C V supply. The contacts, of contactor remains closed king as the current of the operating oil is maintained, but springs open when this current is interrupted. As the switch contacts separate, an are forms between the contacts. Contacts which are open, when the coil is de-energized are known as normally open contacts and indicated by two short parallel lines. Contacts which are closed, when the coils de-energized are called normally close contacts and are indicated by slant line drawn across the parallel lines.

When we press the ON push button, the coils energized and its N.O contacts are closed and N.C contacts are in open position. But when coil is de-energized, these contacts, goes back to in normal condition. These contacts (N.O, N.C) are known as auxiliary contacts. Auxiliary contacts operate with the movement of the main contact. The auxiliary contact (N.O) act as a sealing circuit around the normally open start push button, when the motor is operating. This contact is called sealing or holding contact. The main difference between magnetic contactor and magnetic starter is that, the magnetic starter is equipped with protection devices, such as a overload relay. Contactors are consists on main circuit and control circuit. The contactor is design on the method of energization to its control circuit; e.g. electromagnetic, pneumatic and electro pneumatic type.

If the contacts of a magnetic contactor are damage due to opening and closing, then replace the contacts or repair the contacts. Always use the correct size of magnetic contactor for motor circuit; if we use low rating magnetic contactor motor circuit, its contacts ate melted due to passing of high current through them.

If the coil of contactor is burned, we replace it with equal rating of new coil. Magnetic contactors are available in voltage ratings. DC contactors are same as A.C contactors. The only difference is that a blow-out coil is in series with the main contacts in D.C magnetic contactor. The function of this blow- out coil is that, when contacts are open, an arc forms between contacts, which is blown rapidly upward by the field of the blow-out coil, transfers to the arcing horns and continues to rise until it breaks the are life being of the order of 0.01 sec.