As contactors are used for high-current load applications they are designed to control and reduce the arc produced when the heavy motor currents are interrupted. Other than the low current contacts, they are also setup with Normally Open contacts. These are devices which handle more than 20 Amperes current and over 100 Kilo Watts power.

The contactor has an AC/DC supply driven coil input. This will depend on the requirement. This coil will mostly be controlled by a lower voltage PLC. They can also be controlled by the motor voltage. The motor may have series of coils connected to either control the acceleration or even the resistance.

When current is passed through the contactor, the electromagnet starts to build up, producing a magnetic field. Thus the core of the contactor starts to wind up. This process helps in energizing the moving contact. Thus the moving and fixed contacts make a short circuit. Thus the current is passed through them to the next circuit. The armature coil brings in high current in the initial position. This reduces as soon as the metal core enters the coil. When the current is stopped, the coil gets de-energized and thus the contacts get open circuited.


When selecting contactors, you’ll use one of two common standards: NEMA or IEC. Both match a contactor with the job it has to do, but they do so in different ways.

The NEMA selection process always results in a choice of a contactor you can use over a broad range of operating conditions. For example, you could use a NEMA Size 5 contactor to run a 50-hp motor operating at 230V or a 200-hp motor at 460V.

Using IEC standards, however, you can size contactors very close to their ultimate capabilities. In many cases, this precision allows you to predict how long they’ll last. For example, an IEC-rated contactor may run a motor that draws 40A at full load. In that duty, it should last for more than two million operations. But, if you used it for consistent jogging and plugging, you’d have to replace it after just a few thousand operations.

A contactor is a relay that is used for switching power.
They usually handle very heavy loads like an electric motor, lighting and heating equipments and so on.
Though their output is used for switching very high loads, they are controlled by a circuit with very less power.
According to the loads they handle, they vary in sizes from a small device to as huge as a yard.
Though they are used for switching purposes, they do not interrupt a short-circuit current like a circuit breaker.
They have ratings ranging from a breaking current of a few amperes and 24 DC volts to thousands of amperes with many kilo volts.