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Difference Between Relays and Contactors

Updated on March 29, 2016

Introduction

Relays and contactors are electrically operated switches basically used in control circuits. These are controlled by an external power source or signal. Even though they are performing switching operations they are different from each other in terms of construction, characteristics and operation. Here are the similarities and dissimilarities between Relays and contactors. Let us see one by one.

Constructional details of Relays

Schematic diagram of a relay
Schematic diagram of a relay
Parts of a relay
Parts of a relay

Relays- Operational Pricinciple

Relays are used for the switching in control circuits and switching of light loads (up to 20A). A relay consists of set of contacts, an armature, an electromagnetic coil and an external envelope to protect the internal parts from the external environment. When ever the operational voltage is applied applied to its electromagnetic coil, the coil gets magnetized and attracts the armature which in-turn closes the coil. This is the operational principle of relays. The contacts of a relay are usually marked as NO/NC (Normally Open/ Normally Closed). This defines the status of the relay contact when its coil is de-energized. Selection of relays depends upon its application.

Contactors

Contactors - Operating priciple

Contactors are used for the switching of power circuits such as motor supply, lights etc. They are designed to carry heavy currents and extinct the arcs formed during switching operations. The operating principle of contactors and relays are the same. A contactor contains an electromagnetic coil, an armature, and contacts enclosed in an air tight container. Whenever the electromagnetic coil is excited, it attracts the armature and closes the contacts. Contactors have more rugged construction than relays. Based on the application contactor power ratings are chosen. Hence contactors have the capacity to bare heavy loads for which it has been designed. Contactors are available upto 12500A. One can find these contactors in pump starters at home.

Differency between relays and contactors

Relays
Contactors
Relays are small switching devices used in control circuits
Contactors are also control devices used to switch heavy loads such as traction motors, pumps, capacitor banks, lights etc
Relays contacts can allow only a small current i.e. upto 12A
Contactors are designed to carry heavy current up to 12500A
Smaller and compact when compared to contactors
Contactors are larger than relays

Operation of Relays and contactors

Credit: Electrical Classroom
Credit: Electrical Classroom

What is common with Relays and Contactors?

The facts that are common to relays and contactors is their operating principle, constructional features and the fact that both of them are electrically controlled switching devices.

Summarizing the differences between relays and contactors

I would like to summarize the difference between relays and contactors as below:

  • Relays and Contactors are electrically controlled switching devices.
  • They are operated using an external supply.
  • The only difference between them is their power rating.
  • Power rating of contactors are more than the relays.
  • Hence contactors are used in the switching of heavy loads and power circuits whereas relays are used in the switching of lighter loads and control circuits.

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Comments

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    • goodnews11 profile imageAUTHOR

      OSBERT JOEL C 

      3 years ago from CHENNAI

      Thank you Larry.. Keep reading..

    • Larry Rankin profile image

      Larry Rankin 

      3 years ago from Oklahoma

      I always enjoy learning about this technical information from you.

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