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Squirrel Cage Motors and ABB Softstarter Handbook

Modern electrical motors are available in many different forms, such as single-phase motors, three-phase motors, brake motors, synchronous motors, asynchronous motors, specially customised motors, two-speed motors, three-speed motors, and so on, all with their own performance and characteristics.

ABB Softstarter Handbook
ABB Softstarter Handbook

For each type of motor, there are many different mounting arrangements, for example, foot mounting, flange mounting or combined foot and flange mounting.

The cooling method can also differ very much, from the simplest motor with free self-circulation of air to a more complex motor with totally enclosed air-water cooling with an interchangeable cassette type of cooler.

To ensure a long lifetime for the motor it is important to keep it with the correct degree of protection when under heavy-duty conditions in a server environment.

The two letters IP (International Protection) state the degree of protection followed by two digits, the first of which indicates the degree of protection against contact and penetration of solid objects, whereas the second state the motor’s degree of protection against water

The End of the Motor Definition
The End of the Motor Definition

The end of the motor is defined in the IEC standard as follows:

  • The D-end is normally the drive end of the motor.

  • The N-end is normally the non-drive end of the motor.

Note that in this handbook we will focus on asynchronous motors only.


Squirrel Cage Motors

This book concentrates on the squirrel cage motor, the most prevalent motor type available. It is relatively inexpensive and typically incurs low maintenance costs.

The market features a diverse range of manufacturers offering products at various price points.

Not all motors match the performance and quality of, for instance, ABB motors. High efficiency leads to considerable energy cost savings over the motor's lifespan. Additionally, the low noise level is increasingly important today, as well as the capability to endure harsh environments.

Squirrel Cage Motors are often the overlooked workhorses of industrial applications, silently driving a wide range of machinery and equipment in various sectors. Although they are widespread, their operation and significance remain unclear to many. We will explore the intricacies of squirrel cage motors, including their functionality, uses, benefits, and constraints.

What is a Squirrel Cage Motor?

A squirrel cage motor is a type of induction motor, named for its rotor's resemblance to a squirrel cage. It is the most common type of AC (alternating current) motor used in industrial settings due to its simplicity, ruggedness, and reliability.

At its core, a squirrel cage motor consists of two main parts: the stator and the rotor. The stator is the stationary part of the motor and contains a series of wire windings that produce a rotating magnetic field when supplied with alternating current. The rotor, on the other hand, is the rotating part and typically consists of a cylindrical core made of steel laminations with conductive bars or "squirrel cage" conductors embedded in it.

How Does It Work?

When AC power is supplied to the stator windings, it generates a rotating magnetic field. This magnetic field induces a current in the rotor bars due to electromagnetic induction. The interaction between the magnetic field and the induced current in the rotor bars creates a torque, causing the rotor to turn. This rotational motion is what drives the connected machinery or equipment.

Unlike other types of motors, such as DC motors, squirrel cage motors do not require brushes or slip rings for the transfer of electrical power to the rotor. Instead, the induction process is entirely self-contained within the motor's design, making it simpler and more robust.


Squirrel cage motors find application in a wide range of industrial and commercial settings, including:

  1. Pumps and Compressors: These motors are commonly used to drive pumps and compressors in industries such as water treatment, HVAC (heating, ventilation, and air conditioning), and manufacturing.

  2. Fans and Blowers: They power fans and blowers for ventilation systems in buildings, factories, and industrial processes.

  3. Conveyors and Machinery: Squirrel cage motors are the workhorses behind conveyor belts, mixers, crushers, and other machinery used in manufacturing and material handling.

  4. Industrial Automation: They are integral components of automated manufacturing processes, powering conveyor systems, robotic arms, and other automated equipment.

  5. Utilities: Squirrel cage motors are also used in utilities for applications such as driving pumps in water distribution systems and generating power in hydroelectric plants.


  • Robust and Reliable: Squirrel cage motors have a simple and rugged construction, making them highly durable and resistant to wear and tear.

  • Low Maintenance: Since they do not have brushes or slip rings, squirrel cage motors require minimal maintenance, reducing downtime and operational costs.

  • High Starting Torque: These motors are capable of providing high starting torque, making them suitable for applications requiring heavy initial loads.

  • Efficient: Squirrel cage motors are relatively efficient, converting a high percentage of electrical energy into mechanical energy.


  • Speed Control: Unlike some other types of motors, such as DC motors, squirrel cage motors have limited speed control capabilities.

  • Less Efficient at Low Loads: They may be less efficient when operating at low loads compared to other motor types.

  • Limited to AC Power: Squirrel cage motors are designed specifically for use with AC power sources and are not suitable for applications requiring DC power.

In Conclusion, squirrel cage motors may not be the most glamorous or high-tech motors on the market, but their simplicity, reliability, and versatility make them indispensable in countless industrial and commercial applications. From pumping water to powering conveyor belts, these workhorses quietly keep the wheels of industry turning, demonstrating that sometimes, simplicity is the ultimate sophistication.


ABB Softstarters are electrical devices designed to extend the life of motors by safeguarding them against electrical stress. They come equipped with features for motor starting and protection, ensuring your motor is shielded from a range of loads and network irregularities. Moreover, their compact design and integrated bypass capability contribute to energy savings and reduced heat generation.

Some Softstarter models offered by ABB are:

  • PSTX Softstarters: Ideal for the most comprehensive engine starting applications. It supports all major communication protocols with modbus and anybus modules.

  • PSE Softstarters: The new generation PSE offers the perfect balance between high start-up capacity and cost-effectiveness. Now equipped with built-in fieldbus communication.

  • PSR Softstarters: PSR offers a simple yet reliable startup solution using basic softstart features. It is suitable for applications that require many starts per hour and is perfect for installations that require space saving.

These Softstarters optimize the engine starting process, reducing mechanical stress and increasing production efficiency. Additionally, it ensures the safety of your engine thanks to its engine protection features.

Document Title:

ABB Softstarter Handbook




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