Rotary Switch

What is a Rotary Switch?

A rotary switch is a switch operated by rotation. These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels".

Rotary Switch Terminology 

A rotary switch is electromechanical device which is capable of selecting, making or breaking an electrical circuit 

The angle of throw is the amount of shaft rotation between detent / switch position terminals 

The detent system of a rotary switch provides an operator with a positive indication of rotation from one switch position to the next

Types of Rotary Switch 

THROW 

The number of switch position terminals per pole 

POLE 

The terminal that is common to two or more other switch position terminals 

BREAK BEFORE MAKE CONTACT 

The moving contact breaks the connection with the previous fixed contact before it makes the connection with the next fixed contact 

MAKE BEFORE BREAK CONTACT 

The moving contact makes the connection to the next fixed contact while it is still connected to the previous fixed contact 

Shorting / Non-Shorting Contact Type 

The terminals that remain stationary during shaft rotation are called the fixed contacts 

The contact that rotates from on switch position to the next is called the moving contact 

In a shorting switch the moving contact makes the connection to the next fixed contact before it breaks the connection 

In a non-shorting switch the moving contact breaks the connection with the previous fixed contact before it makes the connection with the next fixed contact

Introduction of Rotary Switch

Rotary switches move in a circle and can stop in several positions. They are used to control many different circuits with a single switch. These devices have some advantages over other switches since turning the actuator can turn circuits on or off depending on the position and many different actuation positions are possible. Rotary switches can also be designed to have many contacts happening at once on a single switch position. While rotary switches can be found on many types of industrial equipment, they can also be found in consumer equipment such as in a car for adjusting things like fan speed. Rotary switches are becoming less common since complex switching operations are being done with digital equipment such as touchscreens. Mechanical rotary switches are still used however, especially in equipment where a computer failure could be a safety issue. 

Rotary switches have a rotating spindle. The rotors are on a spindle and each rotor has an arm projecting outward that can make contact with a terminal when the switch is in a certain position. Depending on the number of rotors, the switch can have dozens of different positions and each one can be attached to a particular circuit. 

In order to put the rotary switch in the proper position, a detent mechanism is used. This mechanism makes the switch "click" into position and stay in place until enough force is applied, preventing the switch from turning freely and being put in the wrong setting accidentally. A detent uses a wheel with notches or grooves cut into it and attached to the rotor. When the wheel reaches the correct position a spring-loaded ball bearing or piece of spring steel pressing against the wheel presses into the groove holding it into place.  

Physical Specifications 

Mechanical Life

Mechanical life represents the maximum life expectancy for rotary switches. Often, electrical life expectancy is less than mechanical life, so please consult manufacturer.

Number of Poles

The number of poles is the number of separate circuits that can be activated at any given time. The term "pole" describes the number of separate circuits controlled by a switch; it is the input or common terminal. The number of circuits controlled determines the number of switch contacts, which in turn determines the poles needed to make or break the contacts. Switches typically have between one and four poles. The most common are a single pole (SP), a double pole (DP), or a triple pole switch (3P). Note that, in the image, the switch is connected to three separate circuits and has three contacts. 

Angle Between Positions

Measured in degrees, the angular distance between positions determines the number of switch positions. For example, a 4-position rotary switch has a 90° angle of throw. For a 100-position rotary switch, the angle of throw is 3.6° degrees.

Number of Decks

The number of decks is the maximum number of decks that can be attached to a common, actuated shaft. They are also called a section, wafer, or module. There are two basic styles: single-deck and multi-deck. Each deck is a round plate with an arrangement of contacts. Single deck rotary switches can control several circuits at a time. Multi-deck rotary switches can control several circuits simultaneously.

Number of Poles Per Deck 

The number of poles per deck is the number of separate circuits that can be activated through a rotary switch per deck. The output connections are usually called ways instead of throws. The construction of the switch provides a total of 12 ways but there may be 1, 2, 3, or 4 poles. The rotating contact will channel the signal from the pole to the output terminals. The number of terminals required determines how many positions a switch will have.

Switch Frame

There are two different frames available for rotary switches: open and enclosed. Open frame switches have visible moving parts which allow for self-cleaning contact systems, ensuring reliable operation. They have more custom contact configurations available and the sections can be sold separately. The internal parts are not visible in enclosed frames; however they offer more protection from dust and contamination. They are generally less expensive and more compact than their open frame counterparts.

Electrical Switch Specifications

Current/voltage rating is the tested amperage and voltage capacity when switching contact positions under load (with current). An electrical arc occurs when switching between positions under load. Over time, this arc may cause contact wear.

Maximum current rating - 

The maximum nominal or nameplate current capacity that a switch will carry with the contacts in a closed position. Current carrying capacity is measured in amps. A switch with the contacts closed has no arc, and the carrying capacity is higher.

Maximum AC voltage rating - 

The maximum AC voltage capacity of a device.

Maximum DC voltage rating - 

The maximum DC voltage capacity of a device.

Actuator Specifications

Bare shaft actuator -

Shaft has no knob, but may be notched to accept various knob configurations.

Knobbed shaft - 

Shaft comes with integral knob.

Flush actuator -

Actuator is flush, meaning it does not project above the switch body. Typically requires a screwdriver for operation.

Keylock - 

Actuation is done with a key or other security or tamper-proof method.

Actuator Features

Actuator detents 

are mechanical mechanisms that hold the switch in a given position after the actuating force is removed.

Integral potentiometers 

include a potentiometer as part of the assembly. Linear potentiometers produce a resistance output that varies according to the displacement or position of a slider or wiper.

Guarded positions 

require a special action, such as pushing or pulling the shaft, in order to change switch position.

Tease-proof mechanisms

prevent a rotary switch from staying between positions after force is removed.

Keylocking toggles 

are used to prevent unauthorized personnel from accidentally shutting off the power, or tampering with the switching or the branch circuit load. They use an open slot instead of a traditional toggle, allowing for the straight insertion of a key that can be toggled up (ON) or down (OFF).

Actuator material - 

The actuator, such as the switch or the switch knob, can be made of a plastic, thermoplastic, or metal material.

Switch Features

Dustproof - 

Resistant to dust.

Momentary on - 

Feature in which the switch maintains its position for only as long as it is positively loaded or actuated; returns to unloaded position when it is let go. Rotary switches with a momentary-on feature can maintain a position during positive loading or actuating.

Optional coded outputs - 

Switch can be configured to provide coded output, such as BCD or Octal.

Weather resistant / waterproof - 

Hermetically sealed against moisture.

Wiping contacts -

Self-cleaning and usually low resistance. Wiping action creates mechanical wear.

Operating temperature - 

The temperature range over which the device must operate.

Binary coded decimal (BCD).
Octal outputs.

Working

Consists of a spindle/rotor with a contact arm or "spoke”.

It has a array of terminals, arranged in a circle around the rotor, each of which serves as a contact for the "spoke" through which electrical circuits can be connected to the rotor.

Applications Examples

• Television
• Oscilloscope
• Radio
• Multimeter etc