What is contactor?

The contactor is an electrical component that serves to connect or disconnect AC power. Contactor or often also called the relay contactor we can find on the electric control panel.

In electrical panels, the contactor is often used as a selector or transfer switch and interlock on the ATS system. Here is a form of contactor that we can meet.

Principle of Contactor:

The working principle of a contactor is like a relay, in a contactor there are several electromagnetic-controlled switches.

In a contactor there are several switches with type NO (Normaly Open) and NC (Normaly Close) and a coil or electromagnetic coil to control the switch.

If the electromagnetic coil of the contactor is given an AC voltage source, the switch on the contactor will be connected, or change its condition, the original FF becomes ON and vice versa which initially ON becomes OFF.

To understand the working principle of a contactor can be seen from the following contactor scheme image:

When the A1 and A2 terminals are given a voltage source, the coil will dance the switch lever on the contactor, each switch with type NO (03 04, 13 14, 23 24) will turn ON and each switch type NC (31 32, 41 42) will be changed to OFF.

NO type contactor switches generally have a capacity to flow larger than the NC contactor type switch.

Types of Contactor:

Contactors that are circulating in the market are generally differentiated based on their ability to control AC voltage.

In the market contactor can be divided into 2 types, namely:

  • 1 Phase Contactor
  • 3 phase contactor

1 phase contactor is used to control the AC 1 phase electric current, while 3 phase contactor is used to control AC 3 phase electricity flow.

In the 1 phase contactor there are at least 2 main switches, while the 3 phase contactor consists of at least 3 main switches.

Applications of Contactor:

  • Lighting control, in large power lighting systems such as those used in music concerts or sports stadium lighting systems with large power lights always use a contactor as a connecting component or an electric circuit breaker to the lighting lamp.
  • Control of an electric motor, a large power 3 phase electric motor such as that used in the industrial world requires contactors as a connecting component or an electric circuit breaker to the motor. The function of the contactor as a control on an electric motor is often referred to as magnetic starter.
  • Transfer switches, transfer switches are systems on ATS. This section always uses contactors because it requires large power control capacity and fast transfer speeds that contactors have.


Instrumentation Engineer

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