This article is all about what is Relay and how it works? we had also mentioned to the point information about Relay type “Electromechanical Relay”. Before going forward carefully learn what is relay. As we know that this age is the age of invention and knowledge. when new electronics are invented, some other electronic devices are also designed for safety measures. so Relay is also one of them. after understanding and reading carefully you will be able to understand ” what is a relay and how it works”?

What is a Relay?

It is an electronic device designed like a switch but the switch work is manually based on the opening and closing of the circuit. The work of relay is based on an electrical signal which is in charge of opening and closing the circuit.

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There are different types of Relays that can be used according to the situation. Some of these types are; Electromechanical and Solid-state. There are many other types but all have the same function.


It is an electrical device that works on the basis of electromagnetism to automatically control the switching mechanism. This relay is used to control high-power electrical machines.

Nowadays mostly electrical machines use an electromechanical relay to control low signals and also controls multiple circuits by only 1signal.


Some of the Electromagnetic applications are the following; the general aviation, aerospace, and wireless technology industries, and there are a lot more devices based on electromechanical relays. This type of relay consists of the following elements;

  • Electromagnet.
  • Mechanically movable contact.
  • Switching points.
  • Spring.
For detail check out the link “what exactly is electromechanical relay?.
Electromechanical Relays




The explanation is based on the image given above as all components are present but need little-bit explanations that are given below:

1: Electromagnet;

Before moving forward know about the construction of the Electromagnetic component. This component is constructed by binding a copper coil on a metal core. Then its ends are attached to the relay and these pins work as DC supply pins.



The other elements such as Mechanical Moveable contact and Switching point are explained together as their work depends on one another.

So There are commonly two more contacts. One is known as Switching points and their function is to control high load Ampere and the other known as Common contact and its function is to attach the switch points.


From the above image contact can be named as:
(NO) refers to normally open, (NC) it refers to normally close, and (COM) it stands for common contracts.


Electromechanical relay can be either operated by using AC or DC.
When it’s operated using an AC relay, then each coil gets demagnetized, each time when the current value is zero. As a result, circuit breaking will take place each time. Now for avoiding such problems the Ac relays are specially designed with a different mechanism that controls the continuity of magnetism. The special AC mechanism is designed with electronic circuits or a shaded coil mechanism.

Working ;

Working of Relay


  • Its main working principle is based on Electromagnetic waves.
  • When Electromagnetic waves are supplied alongside some current then it brings out a magnetic field in its surroundings.
  • The Electromagnetic function brings out by the Copper coil and Iron core in Relay.
  • If the DC current is supplied to the coil it starts attaching as shown in the image. This is known as energizing of the relay.
  • If the current is removed then it moves back to its original position and this state is known as De- energizing.
  • There are also relays totally opposite to the above-mentioned relays such as solid-state relays are having sensors that detect the input voltage and control the output using Opto- coupling.
More clearly the working principle is describe as under:

Working principle of Relay

It operates on the principle of electromagnetic attraction. When the circuit of the relay senses the error in the circuit, it energizes the electromagnetic field which generates the temporary magnetic field.

Working principle of Relay

This magnetic field influences the relay armature for availability or closing the contacts. The small power relay becomes only one contact, including the high power  has two contacts for opening the switch.
The inner section of the relay is shown in the figure subsequently. It has an iron core which is wound by a control coil. The power supply is given to the coil within the contacts of the load and the control switch. The current flows over the coil produce a magnetic field throughout it.
Due to this magnetic field, the overhead arm of the magnet attracts the lower arm. Therefore close the circuit, which makes the current flow through the load. If the contact is already closed, suddenly it moves opposed and hence opens the contacts.

Relay Contact Types

Let’s study about relays contact types. It is also applicable for “Poles and Throws ” terminology. It can be classified on the basis of the number of contacts and the number of circuits.

Poles and Throws

Now Here you must be having a question in your mind that “what are Poles and Throws”?.
The Answer is that every Relay can control one or multiple circuits so each switch is named a pole and A number of circuits to which a relay is attached are known as “throws”.
According to the Poles and Throws, Relay is divided into:
  • Single pole single throw
  • single pole double throw
  • double pole single throw
  • double pole double throw

Single Pole Single Throw

The Single Pole single throw means that the relay is attached to one circuit and one output. Its commonly used in devices that are simply designed for ON and OFF.
Single Pole Single Throw

Single Pole Double Throw

The Single pole double throw means that the relay is attached to one circuit and one output out of two outputs.  It is also named a changeover.
Single Pole Double Throw

Double pole single throw

A double pole single throw means that it is attaching two terminals of a single circuit at the same time.
Double pole single throw

Double pole double throw

The double pole double throw relay is beneficial for phase and polarity reversals as it consists of two poles and two throws.
Double pole double throw
All these Relays will perform their action when its coil is charged or energized.


It can be further divided on the basis of their functions, structure, and application, etc.

Relay Applications

Relays are designed for protection purposes and to control the flow of voltage to the electrical machines. Its also used for changing the high voltage to a low voltage signal for the protection of electrical machines. Examples are Audio Amplifiers and Modems.
Another important function of it is detecting and isolating errors. Some of the area in which Relays are used :
  • stems.
  • Telecommunication.
  • Industrial process controllers.
  • Traffic control.
  • The motor drives control.
  • Protection systems of the electrical power system.
  • Computer interfaces.
  • Automotive.
  • Home appliances.


After going through all the articles you must be able to understand what is a relay? What are its function, types, working, etc?

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