Understanding Electrical Relays: Classification, Structure, and Working Principle

Electrical Relays

Understanding Electrical Relays: Classification, Structure, and Working Principle


Electrical relays play a crucial role in the functioning of various electrical systems. These devices serve as switches, enabling the control and protection of circuits. In this article, we will delve into the classification, structure, and working principle of it. Understanding the inner workings of relays is essential for engineers, technicians, and enthusiasts in the field of related engineering.


I. Classification of Electrical Relays

Electrical relays can be classified based on their working principles, application areas, and contact configurations. The following are some common types:

1. Electromechanical Relays

Electromechanical relays employ electromagnetic forces to control the movement of mechanical contacts, enabling the switching operation.

2. Solid-State Relays (SSRs)

SSRs use semiconductor devices like transistors and optocouplers to achieve electrical isolation and control the flow of current without any mechanical contact.

Electrical Relays
Electrical Relays

3. Thermal Relays

Thermal relays are designed to protect motors and other equipment from overheating by using bimetallic strips or thermistors to sense temperature variations.


II. Structure of Electrical Relays

Electrical relays consist of several key components that work together to achieve reliable switching operations. These components include:

1. Coil

The coil is an essential part of the relay that generates the magnetic field when an electrical current passes through it. This magnetic field actuates the mechanical contacts.

2. Contacts

The contacts in a relay are responsible for making or breaking the electrical connection. They can be normally open (NO), normally closed (NC), or have multiple sets of contacts.

3. Armature

The armature is a movable part of an electromechanical relay that is attracted to or repelled by the magnetic field generated by the coil. It controls the opening and closing of the contacts.


III. Working Principle of Electrical Relays

The working principle of electrical relays varies depending on their type. However, the fundamental concept involves the interaction between the coil, armature, and contacts. Here’s a general overview of the working principle:

1. Electromechanical Relays

When current flows through the coil, a magnetic field is created, which attracts the armature. This movement causes the contacts to change position, either opening or closing the circuit.

2. Solid-State Relays

SSRs use semiconductor devices to control the flow of current. When an input signal is received, the semiconductor switches on, allowing current to flow through.

3. Thermal Relays

Thermal relays monitor the temperature of the equipment. If the temperature exceeds a set threshold, the relay’s contacts change position, interrupting the circuit and protecting the device.



Electrical relays are indispensable components in numerous electrical systems. By understanding their classification, structure, and working principle, professionals in the field can make informed decisions when selecting and implementing relays for various applications. Whether it’s controlling high-voltage equipment or protecting sensitive circuits, it offers versatile and reliable solutions, making them vital in modern-day electrical engineering.

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