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What is a Contactor?

A contactor is an electrical device that is used to turn on and off an electrical circuit. It is regarded as a unique sort of relay. The main difference between a contractor and a relay is that the contractor is utilized in applications that require a larger current carrying capacity, whilst the relay is used in situations that require a lower current carrying capacity. Contactors are small and easy to install in the field. These electrical devices usually have many contacts. When the contactor coil is powered, these contactors are generally open and give operating power to the load. For the most part, contactors are used to regulate electric motors.

Contactors come in a variety of shapes and sizes. Each type has its own set of characteristics, capabilities, and uses. Contactors can handle currents ranging from a few amperes to thousands of amperes, as well as voltages ranging from 24 VDC to thousands of volts. Moreover, these electrical devices come in a multitude of sizes, – from small hand-held devices to all those measuring a meter or yard on one side (approximately).

The contactor is most commonly used in high-current load applications. Contactors are well-known for their capacity to manage currents of more than 5000 amperes and high power of more than 100 kW. When a large motor current is interrupted, it produces arcs. These arcs can be decreased and controlled with a contractor.

Contactor Components-

The contactor is made up of three essential components:

1. Coil or Electromagnet: This is the most essential part of the contactor. The coil or electromagnet of the contactor offers the required driving force to close the contacts. An enclosure protects the coil or electromagnet and its contacts.

2. Enclosure: Contactors, like any other device, have an enclosure that provides insulation and protection against personnel touching the contacts. Polycarbonate, polyester, Nylon 6, Bakelite, thermosetting polymers, and other materials are used to construct the protective enclosure. In most instances, an additional enclosure is built to the open-frame contactor to protect it from severe weather, explosion threats, dust, and oil.

3. Contacts: This is another vital part of this electrical device. The contacts are currently performing the contactor's carrying role. In a contactor, there are mainly three types of contacts: contact springs, auxiliary contacts, and power contacts. Each type of contact has a certain function to perform.

Different Types of Contactor Devices-

1. Knife Blade Switch- In the late 1800s, the knife blade switch was introduced. It was most likely the very first contactor used to control (start or stop) electric motors. The switch was made out of a metal strip that slid across a contact. This switch had a lever that could be used to pull the switch down or up. The knife blade switch had to be lowered into the closed position by standing next to it back then. However, there was an issue with this way of switching. Because it was difficult to manually open and close the switch fast enough to avoid arcing, the contacts wore out quickly. As a result, the soft copper switches began to rust, increasing susceptibility to moisture and filth. The size of the motors became larger over time, requiring the use of larger currents to operate them. As a result, operating such high current carrying switches could be dangerous, posing a major safety concern. Despite the number of technical advances, the knife blade switch was never fully developed due to the challenges and risks of dangerous operation as well as the contacts' short life.

2. Manual Contactor- Engineers created a new contactor device after the knife blade switch became potentially unsafe to use. This contactor device included several functions that the knife blade switch lacked. This device was described as a manual controller.

These characteristics included:

Operation is risk-free.

A unit that is not visible and is appropriately enclosed

Smaller in size

Contacts with single breaks have been replaced by contacts with double breaks.

3. Magnetic Contactor- The magnetic contactor is operated electromechanically and does not require human interaction. This is one of the most advanced contactor designs available, and it can be remotely operated. As a result, it reduces the dangers of running it manually and placing operational staff in danger. The magnetic contactor only requires a small amount of control current to open or close the circuit. In industrial control applications, this is the most common type of contactor.

How Does the Contactor Work?

The electromagnet is activated by the current that flows through the contactor. The contactor core moves the armature due to the magnetic field produced by the excited electromagnet. The circuit between the fixed contacts and the movable contacts is completed by a normally closed (NC) contact. This allows current to flow from the contacts to the load. The coil de-energizes and closes the circuit when the current is released. Contactor contacts are recognized for their quick opening and closing action.

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