What is a Three Point Motor Starter: Working and Principle


Motor starters are the unsung heroes of the electrical world. They are integral to various electrical systems, managing the safe and efficient operation of motors. One special type that deserves attention is the three point motor starter. But what exactly is a three point motor starter? How does it work? And what principles govern their operation? In this blog post, we will explore these questions and delve deep into the world of three point motor starters.

Components of a Three Point Motor Starter

A typical three point motor starter is composed of three main components:

1. Circuit Breaker: This device protects the motor and the system from short circuits and overloads. It can interrupt the current flow in case of an anomaly.

2. Contactor: Acts as a switch that controls the electrical power flow to the motor. It is responsible for starting and stopping the motor based on the control inputs it receives.

3. Overload Relay: This component guards the motor against sustained overloads and faults. It measures the current flowing through the circuit and triggers the circuit breaker to disconnect if the current exceeds a set level.

Each of these components plays a vital role in the operation of the motor starter, ensuring safe and efficient motor operation.

Working Process

The operation of a three point motor starter is a marvel of electrical engineering. Here’s a step-by-step explanation:

1. When the motor is not running, the circuit breaker is open, and no current flows in the circuit.

2. To start the motor, the circuit breaker is closed either manually or by a remote control system. This allows the current to flow to the contactor.

3. The contactor then closes its contacts, allowing the current to flow to the motor, thereby starting it.

4. During normal operation, the overload relay continuously monitors the current flowing through the circuit. If the current exceeds a set limit, the overload relay triggers the circuit breaker to disconnect the circuit, thus stopping the motor.

This process ensures that the motor can be safely started and stopped while protecting it from potential damage due to overloads or faults.

Principle Behind Operation

The operation of a three point motor starter is based on the principles of electromagnetism. When the contactor’s coil is energized, it creates an electromagnetic field that pulls its contacts together, allowing the current to flow to the motor. The overload relay works on the principle of thermal expansion. When the current flowing through the circuit exceeds a set limit, it heats up a bimetallic strip in the relay, causing it to bend and trigger the circuit breaker.

Practical Applications and Uses

Three point motor starters are commonly used in industries where motors are the lifeblood of operations. These industries include manufacturing, mining, construction, and many more. These starters are also used in HVAC systems, water pumps, and various other commercial and residential applications. Their ability to provide safe and efficient motor operation makes them an invaluable tool in these sectors.


Three point motor starters play a crucial role in many areas of our lives, yet they often go unnoticed. They ensure that motors run safely and efficiently, protecting them from potential damage. Understanding their components, working process, and the principles behind their operation can help us appreciate the complex engineering that goes into these devices. Whether you’re an electrical engineering student, a professional electrician, a DIY enthusiast, or just someone interested in electronics, we hope this blog post has helped shed some light on the fascinating world of three point motor starters.

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