Contactor working principle

Guide: A contactor is an automatic control device that uses electromagnetic force to close or open its main contacts, allowing it to frequently switch on and off the main circuit under load. But how exactly does it work? This article will take a deep dive into the inner workings of a contactor — let's get started!

First, the Working Principle of the Contactor – Introduction

A contactor is an electrical device commonly used in industrial power systems. It works by passing current through a coil, which generates a magnetic field that pulls in the contacts, enabling them to close and control the connected load. Due to its ability to quickly disconnect the main circuit and handle high currents, it’s widely used in various electrical applications.

Second, the Working Principle of the Contactor – Classification

Contactors can be classified based on the type of current they handle. They are mainly divided into DC contactors and AC contactors. DC contactors typically use a modular design, allowing customization for specific requirements such as the number and type of contacts. These contactors operate at higher voltages and use a horizontal magnetic field for arc suppression, making them ideal for applications like programmable power supplies, uninterruptible power systems, and construction equipment.

Another way to classify contactors is by their operating mechanism. There are electromagnetic contactors and permanent magnet contactors. Permanent magnet contactors use the repulsion between same-polarity magnets to function, replacing traditional electromagnets with a more energy-efficient system. Examples include models like CJ20J, NSFC1, and NSFC2, which are widely used in modern industrial settings.

Third, the Working Principle of the Contactor – Structure

An AC contactor consists of four main components: the electromagnetic system, the contact system, the arc extinguishing device, and other accessories. The electromagnetic system includes an attracting coil, a stationary iron core, and a moving iron core. The contact system is linked to the moving iron core and usually has three sets of main contacts and one set of auxiliary contacts (normally open and normally closed). The arc extinguishing device helps prevent damage to the main contacts by quickly cutting off the power when needed. Additional parts include an insulating housing, springs, a transmission mechanism, and connection terminals.

Fourth, the Working Principle of the Contactor

When the coil is energized, the static iron core generates electromagnetic attraction, pulling the moving iron core toward it. This motion causes the three main contacts to close, while the auxiliary normally closed contact opens and the auxiliary normally open contact closes, completing the circuit and turning the power on.

When the coil is de-energized, the electromagnetic force disappears, and the spring pushes the moving iron core away from the static core. This action opens the main contacts and re-closes the auxiliary normally closed contact, while the auxiliary normally open contact opens, effectively turning the power off.

Contactor Working Principle