Did you know that there are job categories for contactors? Learn what contactor classes are, what they are and what they are used for, as well as what are the most sophisticated and modern models available on the market.
The contactors are electromechanical and magnetic devices, suitable for each application, they are one of the main equipment used in electrical commands, such as for driving electric machines and motors, where their main function is to control the passage of high currents.
There are two types of contacts, the one used in the command part and the one used for loads. The control unit is used for lower currents, having normally open contacts (NO) and normally closed contacts (NC). The contact used for loads is the power or main contact, which deals with high currents and normally has three contacts (NA). The number of contacts varies depending on the manufacturer.
According to the IEC 947-4 technical standard, job categories for the use of contractors have been established. These categories were made to establish the maximum that a given contactor should establish or interrupt. These categories or classes of contactors have the name alternating current (AC) or direct current (DC), among the most used categories are AC1, AC2, AC3, and AC4.
The categories of contactors basically depend on the type of load and the way in which each one will be activated. For example, the type of motor being started or if resistors will be connected to the contactor. It must also be taken into account the conditions under which the motor closings and openings will be carried out, whether they are in steady-state or starting, reversing the direction of rotation and countercurrent braking.
This category must be applied to all AC devices, as long as the power factor is greater than or equal to 95%. In the case of purely resistive loads, the electrical current of the contactor closing and opening is equal to the nominal current of the load, since there are no transients, that is, the interruption of the current in this type of load is easy due to the low inductive factor. This category of a contactor, as previously mentioned, is used in non-inductive or slightly inductive loads, such as resistance furnaces.
This category is used for starting and stopping, countercurrent braking and impulse starting in-ring motors. When closing, the contactor establishes a current close to 2.5 times the rated motor current. When opening, it must be able to interrupt the rated motor current at a voltage close to the mains, in this case, the interruption is more severe. Starting and stopping ring motors use this category of contactors a lot.
Category AC3 refers to cage engines, which are interrupted with the engine running. When disconnected, the contactor must withstand the motor starting current, which revolves around 5 to 7 times the rated current. Upon opening, the contactor ends up interrupting the rated motor current under a voltage of approximately 20% of the rated mains voltage.
This category of contactors is used in elevators, escalators, conveyor belts, air conditioners, compressors of all types, pumps, mixers, air conditioners, and various other applications.
Contactors of category AC4 refer to countercurrent braking systems and impulse starting systems in a cage or ring-type motors. The contactor closes under a current intensity in the order of 5 to 7 times the rated motor current when it opens. the moment it interrupts a current of the same magnitude and voltage, also when the motor speed is higher. This voltage can be equal to the mains voltage, so the disconnection is severe and demands a lot from the contactor.
Contactors in this category are used in printing machines, load lifting, metallurgy, lathes, overhead cranes, among others. The choice of the contractor category must be made on a case-by-case basis, analyzing the loads and calculating the currents and voltages involved. Currently, there are several types of contractors for motors and other loads on the market and one of the main manufacturers found in Brazil is Schneider Electric, which offers devices with the best resources for protection, safety, monitoring and motor control, in addition to the easy installation of their components.