What is the contactor? Uses, structure and principles of operation

The contactor is a device that plays an indispensable role in the industrial electrical industry. Let’s find out the basic information about this product in the following article.

What is the contactor?

The contactor is an electrical instrument. If you combine this device with another electric device such as CB, push-button,. . . It is possible to perform the switching of remote electrical equipment manually or automatically. The use of this device has the advantage of extinguishing the arc due to the fast switching of the device contacts, up to 1500 times/hour.

Uses of the contactor?

The contactor is a device with a control function to open and close the power supply to a large capacity device. This device is often used in factories, workshop and production facilities on an industrial scale in general.

Structure of a contactor

A contactor made up of 3 parts:

  • The contacts are parts that carry the current of the contactor. This includes resource contacts, auxiliary contacts, and springs of contacts.
  • Electromagnet (or “coil”) provides power to close the contacts. The casing is the frame containing the contact and electromagnet.
  • The case is made of insulating materials such as Bakelite, Nylon 6. Or they can be made of thermoplastic resins to protect and insulate contacts. This helps protect people safely when exposed to these contacts.

The detailed construction of contactor

Contactor classification:

There are many ways to classify contactors. Some can be mentioned as:

Classifying according to the operation principle:

  • Electromagnetic type
  • Pneumatic type
  • Hydraulic type

Classifying according to the electric current

  • DC
  • AC

Classifying according to the contacts

  • The contact is usually closed
  • The contact is usually open

Contactor Fuji FJ-B32

Contactor Fuji FJ-B32

Contactors’ principles of operation

When powering the contactor coil, the magnetic circuit and coil form an electromagnet. That is, the magnetic circuit is sucked into the magnetic circuit. Due to a dynamic magnetic circuit that interacts with dynamic contacts and control contacts. So the contact system is changed state and maintains this state until the coil loses power. The reason that the magnetic circuit is attracted to the static magnetic circuit is that the electromagnet’s magnet is larger than the spring thrust.

When the power supply is disconnected from the contactor coil, the magnetic circuit will be lost. From this moment, the attraction of the electromagnet is smaller than that of the spring. So the magnetic circuit is pushed upward, causing the contact system to change status. That is, the dynamic contacts open.

Choosing a contactor

Icontactor = Idm Loading *(1,2-1,5)


  • Icontactor is the working current of the contactor.
  • Idm is the rated current of the load when working stably.

Hopefully, the contactor information in this article is useful to you. Don’t forget to read many other articles to update new knowledge every day.