Centrifugal Switches

A centrifugal switch is a type of electrical switch that makes use of centrifugal force created from a rotating shaft as means of operation. The switch is designed for activating or de-activating as a function of the rotational speed of the shaft.


The switch consists of two parts:

• A centrifugal mechanism that rotates on the motor shaft and interacts.
  
  
• A fixed stationary switch with electrical contacts that controls the start-winding circuit. These switches are used in induction motors for disconnecting the starting winding of the motor, once it reaches its normal operating speed.

Operating Mechanism
A centrifugal switch operates and is actuated by speed only. A simple type of switch consists of a speed-sensing units that can be mounted directly onto a rotating shaft and a stationary-contact switch assembly. The basic control element in the switch, is a conical-spring steel disc, which has a centrifugal weights fastened to the outer edge of its circular base.

Fingers on the spring are fixed to an insulating spool, which rides free of the shaft and actuates the movable switch contact. After the rotating sensing unit reaches switching speed, the centrifugal force of the calibrated weights overcomes spring force, thus resulting in an instant axial displacement of the spring and the contact-actuating spool.

The contacts switch at one speed, as the speed increases from zero to operating speed level, and move at a lower speed as rotation then slows from operating speed towards zero. The spring decreasingly opposes centrifugal force as the rotational speed increases from standstill until the snap-over point is reached. Finally, the spring force adds to centrifugal force to axially snap the spool and actuate the contacts.

Centrifugal Switches Advantage
These switches have the following advantages:

• Crisp snap-action of the switch mechanism in a tightly controlled range.
• Helps to eliminate creeping, chattering, and reduces arcing of contacts.
• Prevents premature failure and impaired operation with free-floating, frictionless actuator.
• Slim switch design allowing for shortest motor stack.
• Superior life expectancy.