Today’s topic is about contactors! Have you ever wondered what a contactor is? How does a contractor work? And what is the application of a contactor? These questions are very common and in this article, we will answer them, come on guys!
What is a contractor?
Contactors are among the main components in the area of electrical and electromechanical controls. They are used in drives and protection, usually working in conjunction with other accessories and components. Contactors are widely used in motors since their contacts allow the switching of high currents triggered by simple buttons and remote controls.
The contractors are nothing more than a set of contacts that are activated by an electromagnet. They can be Normally Open (NO), Normally Closed (NC) contacts, or switch contacts that switch between Open and Closed (NAF). It is important to make it clear that there are no multi-position switch contacts between the contactors. Then they only have switch contacts in two switching states that are activated (NO) or at rest (NC).
How does a contractor work?
The contactors work through an electromagnetic effect, having three load contacts directly feeding the motors. There is also a block of auxiliary contacts that are used to increase the automation capacity in the command to be executed. It can be fixed to the front or side of the contactor, these characteristics may vary according to the model and manufacturer.
An example of the benefit of using contractors is to avoid unnecessarily going to the machine to perform any type of work that could endanger the safety of the worker. Therefore, we can affirm that there is greater practicality, besides the comfort in the use of this equipment. With the use of contractors, the possibility of handling equipment remotely opens up, that is, you do not need to have direct contact with the company’s machinery, increasing the levels of protection and safety.
What are the main parts of a contractor?
- Coil – Basically it is a copper winding that creates an electromagnetic field. When the coil is fed through terminals A1 and A2, it promotes the displacement of the ferromagnetic core.
- Core – Basically it is built by sheets of ferromagnetic material and has two parts separated by mechanical action of springs. One of these parts of the core is coupled to the contacts and when there is movement of the core, the command and load contacts of the contactor are activated.
- Contacts – Basically they are metal sheets that have the function of switching, being responsible for the conduction of load currents and control currents. Then, when the contactor coil is without power, the contacts are at rest. And when the coil is energized, the contacts are switched through the movement of the core to which they are mechanically coupled.
- Spring – Basically it is the spring responsible for placing the contacts in the rest position when the coil is disconnected from the power source. Therefore, in this condition the force exerted by the magnetic field on the core is less than the force of the spring, causing the parts of the core to move apart.
Types of contactors
There are several types of magnetic and electromagnetic contactors, and each is suitable for each type of application. Categories AC1, AC2, AC3, and AC4 specify suitable contractors for each type of load and drive. In the sequence, we will talk in detail about each one of them.
AC1 is the category used when the power factor is at least 0.95, purely resistive loads, heating, resistances and others. The interruption of current in this type of load is easy, due to the low inductive factor.
AC2 is the category aimed at starting and disconnecting, countercurrent braking and impulse starting in-ring motors. The contractor is prepared to withstand a current up to 2.5 times the nominal current. The interruption is much more severe and the contactor must withstand.
AC3 is the category for cage engines whose shutdown occurs with the engine running. The starting current can be 5 to 7 times greater than the rated motor current. They are used, for example, in elevators, conveyor belts, escalators, elevators, pumps, mixers or air conditioning.
AC4 is the category for even heavier maneuvers such as on lathes or overhead cranes.
It is very important to understand that the choice of the contactor category must be made on a case-by-case basis. Therefore, it is essential to take the loads into account and calculate the currents and voltages involved. Proper sizing is the most important step to avoid future problems!