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A contactor is an electrical component that is similar to a relay in many way but it typically used in larger scale applications.

Contactors are essentially switches that can be controlled remotely. They can be designed to operate at voltages similar to the control devices that control their state or they can be designed to operate at voltages similar to the loads that they control.

Contactors have features that distinguish it from a standard relay. In most cases, a contactor is designed specifically with high current usage in mind. Other differentiators to relays are as follows:

  • Most contactors are designed to be used in the normally open position. Relays can typically be used in two configurations; normally open or normally closed. There are variations to this but this is typically the norm.
  • Contactors are typically larger than a relay in physical size. Small contactors are typically around the size of a person's hand. Contactors can get much larger than that and are sometimes large enough to require heavy equipment to move from place to place and install.
  • Due to the operating conditions in which contactors are used, there are vastly different considerations that go into their manufacture than go into the manufacture of their smaller cousins, relays. Most contactors have some sort of an arc suppression system included in their design that greatly increases their lifespan.

What is meant by ’normal state’ configuration of a contactor?

The normal configuration of a contactor describes the disposition of the contacts when current is not applied to them. Most contactors are normally open, meaning that they close in the presence of current. There are variations, but this configuration is one of the defining characteristics of contactors and one of the things that separates them from standard relays.

Contactor uses

Contactors are typically used for very heavy duty industrial scale applications and their ratings systems is designed to reflect this. They come in different classifications under IEC 60947-4-1. These classifications are expressed as AC numbers, from AC-1 to AC-4. Other classification systems are also used.

The applications of contactors include starting motors, providing control over furnaces, controlling the speed of very large motors and other large-scale applications.

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