The power contactors are for maximum currents up to approximately 600 A. In general, they have three main contacts of the NA type – normally open, for the operation of three-phase loads and can also be provided with coupled auxiliary contacts. An important factor to be verified in the use of the contactors is the sparks produced by the impact during the switching of the contacts, as this causes the natural wear of the contacts, besides constituting risks to human health. The intensity of the sparks can be aggravated in humid environments and also with the intensity of electric current circulating in the panel. In this way different forms of protection are applied, resulting in a classification of these elements. Basically there are four main categories of employment of contactors:
– AC1: it is applied in ohmic or little inductive loads, as heaters and furnaces the resistance;
– AC2: for drive of induction motors with winding rotor; air motor
– AC3: it is application of motors with cage rotor in normal loads like pumps, fans and compressors;
– AC4: is for heavy maneuvers, such as driving the induction motor under full load, reversing in full gear and intermittent operation.