101 Guide to Mechanical Switches
A Switch is a simple mechanical device that is operated by an actuator, used to make or break an electrical circuit. Switches come in a huge range of styles and configurations suited for even the most specific applications.
The contact configuration helps us identify the number of poles and contacts the switch has. This is important in order for us to correctly identify the switch required for the application.
The contact configuration is abbreviated by a 4 letter code. The first 2 letters are the number of poles and the last 2 letters are the number of throws. The poles represent the number of circuits the switch can operate and the throws are the number of contact points.
The contacts can either be normally open or normally closed. Normally open means the circuit is not complete and only completes once the actuator of the switch is pressed. Normally closed means the circuit is complete and breaks the circuit when the actuator is pressed.
Some switches have both normally open and normally closed contacts, these are called changeover switches and are often used to switch between 2 circuits. An example is a cars indicator switch which can operate the left or the right indicator light.
Tip: Changeover switches can be used in place of a normally open or normally closed switch.
Momentary or Latching
Switches come with 2 different operations. A momentary switch makes or breaks the circuit only whilst the actuator is held down, as soon as you release the actuator it switches back to its original state. A Latching switch makes or brakes the circuit and maintains this position when you release the actuator, you need to press the actuator again for it to switch back to its original state.
An example of a momentary switch is a doorbell because it only rings whilst the button is held down. A light switch is an example of a latching switch because the lights remain 'On' until you press the switch again.
Switches will usually state a contact rating printed on the body, this is the maximum amperage the switch can safely handle at a specified voltage. As the specified voltage increases the current rating will usually decrease. So it is critical to consider both the voltage and current of your circuit when selecting a suitable switch.
It is advisable to always use a switch with a contact rating higher than the current and voltage of the electrical circuit.
Tip: the contact rating is the maximum the switch can safely handle, the switch can be used for lower voltages and currents.
Type of Terminals
Switches come with a variety of different terminals suited for a range of applications. The most common are:
Solder Terminals - As the name suggests they are designed for soldering cable onto the terminals. They are frequently used with push button and low power switches.
Quick Fit Terminals - These terminals are often used with rocker and toggle switches. They are designed to mate with crimp connectors and are popular because they require no soldering, although they can also be soldered. The most common sizes are 2.8mm, 4.8mm and 6.3mm width.
Screw Terminals - Designed for use with ring terminals, these terminals are commonly used with toggle and push button switches. They require a cross headed screwdriver making them a popular choice when soldering is not possible.
The pin terminals are designed for PCB applications and will fit most breadboards or stripboards. They are usually soldered and are most common for DIL, slide, push button and tactile switches.
Type of Switches
Key Switches - Often used for applications where the operation of the switch needs to be restricted. They are available in a wide range of options including momentary or latching and with a varying number of positions and poles.
Micro Switches - Extremely versatile, micro switches are suitable from industrial to consumer applications. They are low cost and require little space. Micro switches come with a variety of different lever styles and usually have a very long lifespan.
Push Button Switches - One of the most common types of switches, push button switches can either be momentary or latching. They come in a huge range of sizes and range from low cost PCB switches to stainless steel designs for attractive panels. Push button switches are often used for industrial applications due to their reliability and ease of operation.
Rocker Switches - The rocker switch name comes from the see-saw action of the actuator when it is pressed. They often feature quick connect terminals and are commonly used for automotive and power applications. The switches are available illuminated and with various contact configurations.
Rotary Switches - Often used in conjunction with a knob, rotary switches feature multiple contacts and are suitable for applications including speed control. The switches are available for PCB or panel mounting, and are useful for more complex switching solutions.
Slide Switches - Commonly used for low power applications, slide switches are a low cost but reliable solution for single or double pole circuits. They are usually suited for PCB or panel mounting applications and are a popular choice of changeover switch.
Tactile Switches - These small switches are often found on PCBs and usually feature SPST contact configuration. They come in a range of different sizes and feature varying button heights for specific applications. Tactile switches are also available in a range of operating forces and sealed to protect against ingress of water.
Toggle Switches - Featuring a lever actuator, the toggle switch is one of the most common and for good reason. They are available in a wide range of sizes for low and higher power applications. The toggle switch is available in a wide range of contact configurations and is popular as both latching or momentary. They are frequently used for automotive applications due to their reliable design and mechanical operation.