Contactors are mechanical, electromagnetically operated, and are made for a high frequency of operation, with the electric arc extinguished in the air, without affecting its operation. As can be seen Gates A61, the contactor consists essentially of a bipartite magnetic core, a movable part and the other fixed and a coil which, when fed by an electric circuit, forms a magnetic field which concentrates in the fixed part of the core and attracts the movable part .

In a simplified way we can say that the auxiliary contactors have their contacts rated for maximum current of approximately 6A and have four to eight contacts, reaching up to twelve contacts. When no current flows through the excitation coil this part of the core is removed by spring action. Electrical contacts are spread solidly to this moving part of the core, constituting a set of moving contacts. Solidarity to the contactor housing there is a set of fixed contacts and the set of fixed and movable contacts can be of the normally open (NA) type, or normally closed (NF) type. Contactors can be classified as power contactors or auxiliary contactors.