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A mechanical switching device used in higher current carrying capacity, having one position of rest (either open or closed) operated otherwise than by hand, capable of making, carrying and breaking overload conditions is called:
1. contactor
2. push button
3. limit switch
4. relay

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Correct Answer - Option 1 : contactor

Contactor:

  • A contactor is an electrical device which is used for switching an electrical circuit on or off.
  • The basic difference between the relay and contactor is that the contactor is used in applications with higher current carrying capacity, whereas the relay is used for lower current applications.
  • Contactors can be field mounted easily and are compact in size.
  • These contacts are in most cases normally open and provide operating power to the load when the contactor coil is energized.
  • Contactors are most commonly used for controlling electric motors.
  • There are various types of contactors, and each type has its own set of features, capabilities, and applications.
  • Contactors can break current over a wide range of currents, from a few amperes to thousands of amperes, and voltages from 24 V DC to thousands of volts.
  • In addition, these electrical devices come in varying sizes, from hand-held dimensions to sizes measuring a meter or yard on one side (approximately).
  • The most common application area of the contactor is high-current load.
  • Contactors are known for their capability to handle currents of over 5000 amperes and high power over 100 kW.
  • Heavy motor currents produce arcs when being interrupted. These arcs can be reduced and controlled using a contactor.

 

Operating Principle of a Contactor:

  • The current passing through the contactor excites the electromagnet.
  • The excited electromagnet produces a magnetic field, causing the contactor core to move the armature.
  • A normally closed (NC) contact completes the circuit between the fixed contacts and the moving contacts.
  • This permits the current to pass through these contacts to the load.
  • When current is removed, the coil is de-energized and opens the circuit.
  • The contacts of the contactors are known for their rapid open and close action.

 

Applications:

  1. Lighting Control
  • Contactors are often used to provide central control of large lighting installations, such as an office building or retail building.
  • To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils.
  • One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.

 

       2. Electric Motor Starter

  • Contactors can be used as a magnetic starter.
  • A magnetic starter is a device designed to provide power to electric motors.
  • It includes a contactor as an essential component, while also providing power-cutoff, under-voltage, and overload protection.

 

Solution:

A mechanical switching device used in higher current carrying capacity, having one position of rest (either open or closed) operated otherwise than by hand, capable of making, carrying and breaking overload conditions is called contactor.

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