Difference between Relay and Contactor

There is a lot of confusions and misinterpretations regarding the difference between relay and contactor around the industry as they are two closely related terms. Many times these two terms are used nearly interchangeably. Both of them are electrically operated switches and mainly used for control and switching of loads. Although the basic principle of operation of the relay and contactor are the same.

By this article, we can provide a clear picture regarding the differences between relay and contactor in terms of their application and where they are exactly used.

Difference between Relay and Contactor in tabular form

Relay Contactor
It is used for low voltage switching purposes because relays are usually rated to only 250V. It is used for high voltage switching purposes because contactors are commonly rated for up to 1000V.
The size of a relay is small. The size of a contactor is large.
It cannot be repaired. It can be repaired.
A relay has a common contact that connects to a neutral position A contactor joins two poles together, without a common circuit between them.
It is used in circuits with lower current capacity (maximum 20A) It is used in circuits with low and high current capacity up to 12500A
Relays do not have an arc suppression system built-in. Contactors have inbuilt arc chutes for suppression.

What is Relay?

Relays are basically sensing device, which detects abnormal conditions in an electric circuit such as faults and sends a signal to operate circuit breaker to isolate faulty equipment from the entire system as quickly as possible.

Types of Relay

Now depending upon the time of operation and construction, a relay may be classified as follows:

1. Based on the time of operation

  1. Instantaneous relay
  2. Definite minimum time relay
  3. Inverse relay
  4. Inverse definite minimum time relay

2. Based on the construction

(i) Electromagnetic attraction type

  1. Balanced beam type
  2. Moving plunger-type
  3. Attracted armature type

(ii) Electromagnetic induction type

  1. Shaded pole type
  2. Induction cup type
  3. Wattmeter type

(iii) Gas-operated relay: Example – Buchholz relay.

(iv) Thermal relay: mainly used for overload protection.

(v) Static/microprocessor-based relay

What is Contactor?

A contactor is basically a special type of relay which is mainly used for switching an electrical circuit on or off. When the contactor coil is getting energized then it will provide operating power to the load. They are most commonly used for controlling electric motors and lighting applications. Contacts are a very important component of the contactor. The contacts are classified as power contact, auxiliary contact, and contact spring. The materials used for the contacts have stable resistance and high welding resistance. There are also two types of power contact; stationary and movable contact.

Types of contactor

Depending upon various contacts, It may be classified into three types i.e.

(i) Power contactor

(ii) Auxiliary contactor

(iii) Definite purpose contactor

Author
Susmita Ghosh

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