Centrifugal Switch and Its Function

In single-phase induction motors, especially split phase and capacitor start motors, a centrifugal switch is an important component used for proper starting and operation. In the ITI Refrigeration and Air Conditioning (RAC) trade, understanding the centrifugal switch is essential for motor maintenance and troubleshooting.

Introduction

A centrifugal switch is a mechanical device mounted on the motor shaft that operates based on centrifugal force. It is mainly used to disconnect the starting winding (auxiliary winding) from the circuit after the motor reaches a certain speed.

Construction of Centrifugal Switch

• Mounted on the motor shaft
• Consists of rotating weights (flyweights)
• Spring mechanism
• Contact points (switch contacts)
• Stationary and moving parts

The switch is usually located inside the motor housing and is connected in series with the starting winding.

Working Principle

The operation of a centrifugal switch is based on centrifugal force generated by the rotating shaft.

Starting Condition

• When the motor is OFF or just started, the speed is low.
• The centrifugal force is not enough to move the weights.
• The switch remains closed.
• The starting winding is connected to the circuit.

Running Condition

• As the motor speed increases (around 70–80% of rated speed), centrifugal force increases.
• The weights move outward due to rotation.
• This action opens the switch contacts.
• The starting winding is disconnected from the circuit.

Functions of Centrifugal Switch

• Disconnects starting winding after motor starts
• Prevents overheating of starting winding
• Improves motor efficiency
• Ensures smooth transition from starting to running condition

Applications

• Split phase induction motors
• Capacitor start motors (CSIR, CSR)
• Refrigerator compressors
• Air conditioning motors

Common Faults

• Switch stuck in closed position (starting winding remains connected)
• Switch stuck in open position (motor fails to start)
• Worn or burnt contacts
• Spring failure

Maintenance

• Keep contacts clean
• Check proper movement of weights
• Inspect spring condition
• Avoid dust and moisture inside motor

Conclusion

The centrifugal switch plays a crucial role in the operation of single-phase motors by disconnecting the starting winding after the motor reaches sufficient speed. Proper functioning of this switch ensures efficient motor operation and prevents damage to the starting winding.

Understanding its construction and working helps RAC students in diagnosing motor faults and performing effective maintenance.