What is Contactor?

Definition of contactor:


It is a cutting and control device generally driven by means of an electromagnet, designed to perform a large number of manoeuvres, in circuits with currents and powers that can reach relatively high values.

It is a mechanism whose mission is to close contacts, to allow the passage of current through them, and to open other contacts to prevent the passage of current through them. This occurs when the contactor coil receives electrical current, behaving as an electromagnet and attracting said contacts

They can be controlled remotely by means of push-buttons or automatically by means of detectors such as thermostats, limit switches, buoy, etc.,

Construction of Contactor:

Main Components:

  • Main contacts or poles: Their purpose is to open or close the force or power circuit. These contacts are identified by the standardized indexes for each contact with the numbers: 1L1, 3L2 and 5L3 for the part where the voltage supply lines are connected and 2T1, 4T2 and 6T3 for the side where the load is connected.

  • Auxiliary Contacts: They are used in the control circuit or maneuvers, for this reason they will support less current intensity than the main contacts. These contacts are identified by the standardized indices for each contact with the numbers: 13-14, 43-44 for open contacts (NO) and 21-22, 31-32 for closed contacts (NC).

They are of 2 types:

  • Normally Open (NO) - the contacts are open and close when the electromagnet is powered.

  • Normally Closed (NF) - the contacts are closed and open as soon as the electromagnet is powered.

  • Electromagnet: it is the motor organ of the contactor. It comprises a magnetic circuit and a coil


As soon as the control circuit is closed (by pressing a push-button, for example), the current flows through the electromagnet coil of the contactor. This chain creates a magnetic field that will pull the entire structure up and overcome the force spring, causing the contacts fixed and moving contacts to touch.

Under these circumstances, the IO current can flow from the left (phase) to the right (charge/motor) and put the power circuit (motor) running.

As soon as we interrupt the control circuit (by pressing another push-button, for example), the current stops crossing the coil of the contactor electromagnet, which causes it to stop exerting force on the above structure and thus the force of the moving contact is pulled upwards and is no longer in contact with the terminals fixed contact, which causes the IO current to stop flowing and the load/motor is no longer fed and stops.