Normally Closed Contactor: Definition, Working Principle

What is a normally closed contactor?

The normally closed contactor is a type of special product that allows the current to pass through its main contacts when the contactor coil is not energized. When voltage is applied to the coil, its main contacts open and interrupt the current. It’s mainly used in lighting, crane, and safety applications.

This contactor’s main contacts have only one rest position: Closed

The working principle of a normally closed contactor is the opposite of a normally opened contactor which is the usual type of the automation industry. In normal operation, the normally closed contacts on the contactor remain closed allowing continual power to the load. When the contactor coil is energized, the main contacts disconnect the mains power from the load.

The main structure of a normally closed contactor

Electromagnet

It can attract the moving core by controlling the attraction force. It does this by deriving magnetic flux from running current through the coil installed around the core.

Coil

To derive magnetic flux, the coil is installed around the core, derived magnetic flux changes by frequency, but in the small devices, it can be applied with one coil at 50, 60Hz.

Switching part

It is a part breaking or flowing a load current and consists of a moving point, a fixed point, and grid it has a structure to send arc to the grid and make the arc discharge by making use of electromagnetic force for breaking circuits quickly derived by running current.

Circuits of a normally closed contactor

Auxiliary circuit

All the conductive parts of a contactor are designed to be inserted in a different circuit from the main circuit and the contactor control circuits.

Control circuit

All the conductive parts of a contactor (other than the main circuit and the auxiliary circuit) are used to control the contactor’s closing operation or opening operation or both

Main circuit

All the conductive parts of a contactor are designed to be inserted in the circuit that it controls

Note that!

Sometimes a normally closed contactor can be called “a standard contactor with a normally closed auxiliary contact.”