Difference between relay and relay module

Last Updated on April 1, 2024 by Nasir Hanif

Relays are essential components in electrical automation systems, whether industrial or home. The relay was invented in 1835 by American electromagnetism scientist Joseph Henry. It is a remote switch controlled by current, magnetism, or temperature.

What is a relay?

It is an electrical switch that opens and closes circuits electromechanically or electronically. Relays perform different tasks in industrial control applications such as switching, separating, amplifying, multiplying, etc. Relays are of essentially two types electromechanical (EMR) and solid-state (SSR). Both types of relays remain immensely popular. However, the usage totally depends on the electrical requirements of the consumer.

It functions on the principle of electromagnetic attraction. In EMR, contacts open or close by magnetic force, while in SSR, switching happens electrically and does not contain contacts.

When the relay circuit senses the fault current, it energizes the electromagnetic field, which produces a temporary magnetic field. It permits the transferable contacts to make or break a connection with the fixed connection. When the relay is de-energized, closed contacts automatically start and break the connection and vice versa. While the small-power relay contains only one contact, the high-power relay includes two contacts for opening the switch.

What is a relay module?

However, the relay module is different from the relay. A relay module comes with an array of one or more relays.



These relays are developed with electrical, mechanical, and magnetic components. They are created with a coil that generates a magnetic field when energized. This magnetic field attracts the armature, which closes or opens the contacts.


Solid-state relays are circuits with various electronic components that have the same operation as the earlier Electromechanical relay. They use solid-state elements to execute the switching process without any moving parts.

Parts of Electromechanical Relay

An electromechanical relay comprises a wire loop folded over a soft iron core, or solenoid, an iron yoke that delivers a low reluctance path for magnetic motion, a flexible iron armature, and sets of contacts. 





Parts of SSR

Input circuit


Output driver circuits

Semiconductor switching devices

Types of Electromechanical Relays

General Purpose Relays

Reed Relays

Machine Control Relays

Types of Solid-State Relays

Zero-Switching Relays

Instant On Relays

Peak Switching Relays

Analog Switching Relays

Functions of Relay

The relay module comprises three high voltage terminals on one side: Normally Closed (NC), Common terminal (C), and Normally Open (NO). These terminals attach to the device that you want to handle. The other side also has three low voltage pins, Ground, Vcc, and Signal, that join Arduino.

Relay applications

Lighting control systems

Home appliances


Industrial process controllers

Traffic control

Motor drives control

Protection systems of electrical power system

Computer interfaces


Channel Types

Single Channel Relays

Dual-Channel Relay Module

Four-Channel Relay

8-Channel Relay Module


Relays and relay modules are used to control a circuit by an independent low-power signal or several circuits by one signal. So, it is important to choose between relay and relay modules per needs.

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