Electric circuits are the backbone of electronics, and they may be managed through various ways. The use of contactors is a primary method of circuit control, such components being capable of making or breaking the connection between a power supply and load. While similar to relays in their functionality, there are certain differences that set them apart. As contactor components come in various forms and are extremely common to electrical circuits, it can be useful to have a general understanding of their functionality and applications.
As a type of electromechanical switch, a contactor may be controlled electrically, generally requiring less power than the switched circuit that it is managing. Contactors may be employed for a number of systems, commonly finding use in the control of electric motors, lighting fixtures, heating, capacitor banks, thermal evaporators, and much more. In order to accommodate varying applications, contacts come in a range of sizes and capacities, some being very small while others can reach upwards of a meter in length. Additionally, breaking current may range from a few amperes to thousands.
The knife blade switch is the oldest form of contactor, taking advantage of ON and OFF electric motors for its processes. With manual operation, a lever is used to pull a metal strip up and down. Due to their various drawbacks such as their sensitivity to moisture and their safety risks, such components were soon superseded.
The manual contactor followed, improving upon various drawbacks of the previous system. With a properly enclosed unit, such devices could be manually controlled for the means of varying operations while remaining safe to use. Due to the use of double break contacts, the manual contactor is capable of opening a circuit in two places at once, increasing its ability to provide current in a smaller size package.
The magnetic contactor is the most recent addition, such devices commonly being found in various industrial applications. Unlike previous devices, the magnetic contactor is capable of automatic operation, making it quite beneficial and safe to operate. Additionally, the magnetic contact can function with the least amount of control current, allowing for the opening and closing of a circuit to be more efficient.
Across all contactors, the essential components that make them up are their contacts, a coil or electromagnet, and the frame or housing. The contacts serve to carry current, coming in the form of stationary and movable types. Generally, the materials for such components exhibit high welding resistance and stable arc resistance, also being capable of withstanding mechanical stress and erosion.
The coil, meanwhile, acts as the driving force that closes contacts. With a coil wound around an electromagnetic core, the coil can serve as an electromagnet. With the use of a fixed part, a movable component, and a spring connecting the two, the assembly can conduct operations as a spring return mechanism. An armature is also connected to the movable part, and contacts will connect when the force of the coil overtakes the spring force. Meanwhile, the contacts will disconnect when the spring force is higher. From an external source, the input of the coil is either AC or DC depending upon the application and assembly.
The enclosure is the final major component, ensuring that all internal elements of the contactor are well protected. Generally, the enclosure blocks out dust, moisture, and other various contaminants that may be detrimental to the health of the assembly. Additionally, the enclosure also prevents anyone from touching the contacts themselves, furthering safety.
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