What is Relay and How it works in detailed explanation

What is Relay?

A Relay is an electromagnetic switch that is used to turn on and turn off a circuit by a low power signal, or Simply relay is a switch which controls (open and close) circuits electromechanically. The main operation of this device is to make or break contact with the help of a signal without any human involvement in order to switch it ON or OFF. It is mainly used to control a high powered circuit using a low power signal.

A relay is an electromechanical device having electrical, magnetic and mechanical components. The relays control the electric circuit by opening or closing the contacts of that circuit. An electromechanical relay consists of three terminals namely common (COM), normally closed (NC) and normally opened (NO) contacts. These can either get opened or closed when the relay is in operation. These relays can work on both AC and Dc supply sources.

When No Current Passes:

com always connected to Nc
When no Current passes through COil, the Com/pole is always connected to NC(Normally connected)pin .


When Current Passes:

As  current is passed through the coil, the pole gets connected to NO pin of the relay.(Normally open)when current passes com to no

How Relay Works

In any type of electromechanical relay of the relay, the major components are coil, armature and contacts. A piece of wire is wound around a magnetic core so it forms an electromagnet

When the supply is given to this coil, it becomes energized and produces an electromagnetic field. An armature is a movable part and its main function is to open or close the contacts. It is attached with a spring so that under normal working condition this armature comes back to its original position and the contacts are the conducting parts which connects the load and source circuits.
how relay works

Relay Basics

The basics for all the relays are the same. There are two colours shown. The green colour represents the control circuit and the red colour represents the load circuit. A small control coil is connected onto the control circuit. A switch is connected to the load. This switch is controlled by the coil in the control circuit. Now let us take the different steps that occour in a relay.

4 pin relay ark

•Energized Relay (ON)

As shown in the circuit, the current flowing through the coils represented by pins 1 and 3 causes a magnetic field to be aroused. This magnetic field causes the closing of the pins 2 and 4. Thus the switch plays an important role in the relay working. Thus, when the electrical relay in energized the current flow will be through the pins 2 and 4.


•De – Energized Relay (OFF)

As soon as the current flow stops through pins 1 and 3, the relay switch opens and thus the open circuit prevents the current flow through pins 2 and 4. Thus the relay becomes de-energized and thus in off position.


In simple, when a voltage is applied to pin 1, the electromagnet activates, causing a magnetic field to be developed, which goes on to close the pins 2 and 4 causing a closed circuit. When there is no voltage on pin 1, there will be no electromagnetic force and thus no magnetic field. Thus the switches remain open.

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