Contactors

A contactor is a switch which is magnetically closed. Contactors are the fundamental constituent units of a motor starter. Contactors are also used in some other devices like furnaces, capacitors, heaters etc. The basic components of a contactor are an electromagnet, a movable core, an arc quenching structure and sets of stationary and moving contacts. There are four types of contactors. They are solenoid type, clapper type, lock-out type and inductive accelerating type. Lock-out type and inductive accelerating type are used in dc motor controls. Solenoid type and clapper type are important categories. In a solenoid type contactor, movable contacts are attached to the movable core of a magnet. On supplying energy to electromagnetic coil, movable core gets pulled towards the stationary core which forces contacts to close. To create an out of phase flux to hold the magnet closed during zero points of alternating current, pole face of the magnet are provided with shading coil. In clapper type contactors, the movable contacts are mounted on a hinged movable armature. Lock-out contactors are used for cutting the resistance of the armature circuit of a motor in steps.