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The Different types of contactors

What is a contractor?

A contractor is an electrical device that switches an electrical circuit on or off. Generally, these devices feature multiple contacts. When the contactor coil, these contacts are in most cases normally open and provide operating power to the load.


What are the contactor components?

Here are three of the contractor's crucial components:

  1. Coil or Electromagnet – The coil or the electromagnet of the contractor provides the driving force that is required to close the contacts. This is the most crucial component

  2. Enclosure – The contactors feature an enclosure, which provides insulation and protection from personnel touching the contacts. The protective enclosure is made from different materials

  3. Contacts – This is an important component of this electrical device as well. There are different types of contacts in a contactor, each type has an individual role to play – Contact springs, auxiliary contacts and power contacts. The current carrying task of the contactor is done by the contacts.

What are the different types of contactor devices?

Knife Blade Switch:

This type of contactor is probably the first contactor that was used to start or stop electric motors. The switch was made of a metal strip, which would drop onto a contact. It had a lever for pushing the switch up or pulling it down. In that time, one had to stand next to the knife blade switch, to level it into the closed position.

However, this method of switching had a problem. It was difficult to manually open and close the switch fast enough to avoid arcing, so it caused the contacts to wear out quickly. This made the soft copper switches vulnerable to moisture and dirt. Over the years, due to the increasing size of the motors, there was a serious safety concern. There was a need for larger currents to operate the motors which created potential physical danger to operate such high current carrying switches. This is why the knife blade switch couldn’t be fully developed.

Manual Controller:

After the knife blade switch became potentially dangerous to use, engineers came up with another contactor device. This device referred to as a manual controller. It offered features that were missing in the knife blade switch -

  • Physically smaller size

  • Safe to operate

  • Double break contacts

  • Properly encased unit

Double break contacts allows you to work with more current because it can open the circuit in two places at once. The power circuit is engaged when the manual controller is activated by an operator. The switch or button is attached to the controller physically. Once activated, it carries the electricity to the load. The knife blade switches was replaced completely by the manual contactors. Manual contactors are still being used today in different variations.

Magnetic Contactor:

The magnetic contractor is one of the most advanced designs It operates electromechanically and does not require human intervention. It can be operated remotely which helps to eliminate the risks of operating it manually. The magnetic contactor requires a small amount of control current to open or close the circuit. It is the most common type of contactor used.

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