Contactors, what are they?

Contactors are one of the main components in the area of ​​electrical and electromechanical controls. Used in drives and protection (in conjunction with other accessories and components) of electrical machines. Its use is primarily in motors because its contacts allow the switching of high currents activated by simple buttons and remote controls.

They work through an electromagnetic effect, have three load contacts directly feeding the motors, and four auxiliary contacts (which may vary according to the model and manufacturer) for automation and simplification of work, for example avoiding unnecessary going to the machine to perform work that can put worker safety at risk, which adds greater practicality and comfort when using the machine, in addition to allowing the equipment to be handled remotely without direct contact with the company’s machinery, thus providing a degree of protection and security to the professional, who can perform his work without any risk to his integrity.

The contactors are nothing more than a set of contacts activated by an electromagnet, which can be NO (Normally Open), NC (Normally Closed) contacts or NAF switching contacts (Switch between Open and Closed). It should be noted that there are no multi-position switch contacts in the contactors, having only switch contacts in two switching states, activated or at rest, which are NO and NC.

In addition to the three power contacts for powering the motor, all of the NA, there is the auxiliary contact block, used to increase the automation capacity in the command to be executed, making it possible to fix it on the front or side of the contactor.

Main parts of a contactor:

  • Coil:  It is a copper winding that creates an electromagnetic field when fed through terminals A1 and A2 and as a result, it promotes the displacement of the ferromagnetic core.

Contactor coil.

  • Core: It is built-in sheets of ferromagnetic material and consists of two parts. These parts are separated by the mechanical action of springs. One of the parts of the core is coupled to the contacts, so the movement of the core activates the control and load contacts of the contactor .

Core of the Contactor.

  • Contacts: They are metal blades with the function of switching and responsible for conducting load currents and control currents. When the contactor coil is de-energized, the contacts are at rest, when powered, the contacts are switched through the movement of the core to which they are mechanically coupled.

Contactor and Auxiliary Contacts.

The figure below shows the symbology of contactors used in multifilar diagrams. The dashed line represents the electromechanical actuation of the coil (terminals A1 and A2) on the main contacts (terminals L and T) and an auxiliary contact (terminals NO).

Contactor contacts.

The name of the trminals of a coil is always (A1 / A2), that of the contacts will depend on its purposes.

  • Spring: The spring is responsible for placing the contacts in the rest position as soon as the coil is disconnected from the power source. In this condition the force exerted by the magnetic field on the core becomes less than the force of the spring, causing the parts of the core to move apart.

Some of the advantages of using the contactor are its low energy consumption, in addition to being a device that makes it possible to control loads remotely, which avoids unnecessary investment in cables that support high currents and that present a disproportionate voltage drop.

Contactors are used to drive machines and motors, providing safety and convenience in the handling of equipment that may pose risks to the professional’s integrity.