Saturday, September 12, 2015

What is Magnetic Contactor and How It's works

We know that for power wiring / 3 phase motor wiring we use mostly the magnetic contactor or motor starter. In this post we will study the magnetic contactor importance, working / function and it's uses in electrical technology. I also share post about M contactor wiring diagram but this post specially for function and working of 3 phase contactor or motor starter.

What is Magnetic Contactor?

We can also said that a contactor is type of electrical relay which we use for power electric motor to start or stop. Contactor make easy to controlled 3 phase induction motors. We know that 3 phase motor required three phase supply to run, 3 phase supply is two dangerous which we can not handle with a circuit breakers for induction motor. Contactor make easy to handle the 3 phase motor controlling. The parts of the magnetic contactor are coil, iron core, 3 contacts points and NC, NO points.

magnetic contactor

How a Magnetic contacor Works

The function of a contactor or motor starter is simple, when the AC supply goes to the contactor coil, the coil make a strong magnetic field and field pulls the iron core to the coil and make a electrical contacts.

What are NC, NO in Contactor
The NC means the Normally close electric circuit or we can said it is a normally close contacts and NO meas normally open contacts. In normal state when contactor coil does not energize the NC point is normal close state and when the coil energized these these NC contacts create a NO contacts between one another, after coil deenergized NC contacts make a close circuit.
Same the NO contacts change on coil energizing to the NC contacts.

Also read

Advantages of Contactor

There are many advantages of 3 phase contactor but some are very important which are below.
You can controlled power motors easily by pushing a small button.
You can ON/OFF electrical 3 phase motor in small time.
You can safe him self for electric shock in 3 phase motor starting.


  1. Thanks a lot for this easy read.

  2. Sir thank you
    Sir i want to make wireless sensor network based drip irrigation system. Soil moisture sensors will be installed in the field. In system motor size is 7.5 hp and 440 volt water pump. Sir how i can automate this water pump by Contractors or Relay