How to wiring with a 3-phase contactor

The contactor is an intermediate electrical device used to switch off a loading device through the controller. This is a very popular switchgear in the industry. This article will introduce how to start from 3 phases.

Structure and function of the contactor.


A contactor consists of two main parts. The dynamic contact used to shorten the current for the load and suction coil to control the contacts.

what different between A contactor and a CB is they are used to close the load continuously according to the controller’s signal. The contactor controlled by the electric circuit carries the much lower current than switching current. In fact, large power starter kits are more complex. They consist of many enclosed parts to guarantee durability for low-voltage electric tools.


Contactor contacts are divided into main contacts, auxiliary contacts and springs of contacts. The spring acts as the carrier of the current passing through the load. The goal is to seal the arc generated when switching off the large load current. Thereby ensuring durability for the main contact. Auxiliary contacts used to maintain, reduce the current through the coil after the main contact is closed. Because the original energy provided to close the starter is much larger than the energy used to maintain them. That reduces the amount of power significantly, and always maintains the coil in a cool state. In fact, these saving circuits are always available at high power start-up.

Electromagnets (often called suction coils) provide the force to attract dynamic contacts. This includes many wire rings wrapped on an electrical engineering steel core. The current flowing from it will magnetize the iron core to turn into an electromagnet.

Magnetic suppressor consists of coils used to destroy the electric arc. This is important because the arc is always produced when there is a large current change between the contact points of the motor. It creates wholes and wounds the extreme points. Especially for the DC power line. So large ampere contactors are often made much more complicated

How to wiring a 3-phase contactor

Cách đấu khởi động từ 3 pha

The image above shows details of how to wiring a 3-phase contactor in civilian electricity to control water pumps.

The dynamic part of the contactor has 2 input points connected to the power source. Two output contacts are connected to the motor (load). A time timer is adjusted according to the selected user time frame to be connected in series with the suction coil of the magnetic boot.

The process works as follows: When the timer is closed, the circuit will power the suction coil. The electrical contactor will be applied to the pump which will operate for a set period of time then release and finish.

The current in the signal control circuit is much smaller than the dynamic circuit. Therefore it ensures safety for operation and flexibility in a pairing.

Note when wiring the contactor

Clearly, differentiate and isolate the dynamic circuit and control circuit for convenience in later repair. The Cos connectors connect to make sure, safe and aesthetic.

Select the contactor suitable for the capacity of the load, avoid wasting in the selection of electrical equipment. And finally, you should have a diagram of the principle and assembly for the later maintenance and repair more convenient.

Sơ đồ và cách đi dây

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