What is a magnetic starter?

In the realm of electrical engineering, the magnetic starter stands as a crucial device, shouldering the responsibility of controlling the starting, stopping, and safeguarding of electric motors. Its significance in industrial settings cannot be overstated, and to understand magnetic starter thoroughly, we need to explore its key components, working principle, and benefits.

What is a magnetic starter?

A magnetic starter is a vital industrial electrical device integrating key components like electromagnetic contactors, overload relays, control circuits, and enclosures, designed to control motor starting and stopping, enable automatic and remote operation, and provide critical overload protection—ultimately ensuring the safe, efficient, and reliable performance of electric motors in industrial settings.

Key Components​

Electromagnetic Contactor: It consists of a coil, an iron core, and contacts. The coil, when energized, generates a magnetic field that attracts the iron core, causing the contacts to close or open. The contacts are responsible for connecting or disconnecting the main circuit of the motor. This component is the core of the magnetic starter, enabling the on-off control of the main circuit.​

Overload Relay: This component monitors the current of the motor. When the current exceeds the rated value, it will cut off the circuit to protect the motor from damage due to overload. It works by sensing the current through a bimetallic strip or a thermal element, which bends or acts when overheated, triggering the relay to open the circuit.​

Control Circuit: Comprising buttons, switches, and other elements, it is used to control the action of the electromagnetic contactor. For example, the start button, when pressed, completes the control circuit, while the stop button breaks it, thereby controlling the energization and de-energization of the contactor coil.

How it works​

When the start button is pressed: The control circuit is energized. The coil of the electromagnetic contactor gets electricity and generates a magnetic field, which attracts the iron core, causing the contacts to close. As a result, the main circuit is connected, and the motor starts running.​

When the stop button is pressed: The control circuit is broken. The coil of the electromagnetic contactor loses electricity, the magnetic field disappears, and the contacts open under the action of the spring. The main circuit is thus cut off, and the motor stops.​

In case of an overload: The overload relay detects the excessive current. It then acts to cut off the control circuit, leading to the de-energization of the electromagnetic contactor's coil. The contacts open, and the motor stops running to avoid damage.

Benefits of Magnetic Starters​

Automatic Control and Remote Operation: They enable automatic control of motor starting and stopping, and can be operated remotely, which is convenient and efficient, especially in large industrial facilities where manual operation near the motor is inconvenient.​

Overload Protection: The built-in overload relay provides effective protection to the motor, preventing it from being damaged due to excessive current, thus extending the motor's service life.​

High Reliability: Magnetic starters work stably and have high reliability, reducing the occurrence of faults, ensuring the continuous operation of production lines, and improving work efficiency.​

Safety Assurance: The enclosure prevents operators from direct contact with internal live components, reducing the risk of electric shock. Additionally, the automatic shutdown function in case of faults further enhances operational safety.

Conclusion

A magnetic starter is far more than just an on/off switch. It's a sophisticated safety and control system essential for reliable and safe operation of industrial electric motors. By combining a contactor for robust switching, an overload relay for critical protection, and a low-voltage control circuit for safe operation, magnetic starters prevent motor damage, protect personnel, and enable efficient automation in countless applications, from pumps and fans to conveyors and machine tools. They are a fundamental building block of modern industrial electrical systems.