Different Types of Electrical Switches & Their Application

Ed Combs
By Ed Combs
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Electricity changed the world forever, and many of the inventions we take for granted today wouldn’t be possible without electricity. However, the ability to control electricity would not be possible without the electric switch.

If electricity were a train, the switch would be its conductor. We need electrical switches to control electric power. This article will explore the many different types of electrical switches, how they work, explain their rating differences, and review their many applications. 

What is a Switch?

Given that the verb form of the word switch means to change direction or course, it makes sense that a device used to control the flow of electricity is called a switch or electrical switch. The use of electrical switches dates back to the discovery of electricity’s first practical application and the construction of the first electrical circuit.

The electrical switch is essential to using and applying electricity in all aspects of life. It is used to open and close an electric circuit, thereby disabling and enabling the flow of the electric current. Almost all electrical and electronic devices use at least one switch to control their on and off functions. For example, an electric switch is used to turn on and off lights in a building or turn a car’s motor on and off.

Rating of Electric Switches

There are many different types of electric switches; however, their application depends on the ratings of the devices, specifically the current rating and the voltage rating. Therefore, it’s critical to understand how these ratings define different types of electronic switches in relation to their electrical applications.

Current Rating

The current rating is the maximum electric current that a switch is designed to carry. If you select an electrical switch for an application that exceeds this rating, the electric switch and its components may suffer damage, including overheating, deformation, or melting.

Voltage Rating

A voltage rating in different types of switches is the maximum voltage that the switch is designed to withstand. What is voltage? It’s the pressure from a power source that pushes charged electrons (i.e. the current) through a conducting loop or between two points, enabling the current to power something. If you think of it as the pressure in a water line, then the voltage is electrical pressure. Voltage is measured in volts, which is signified by a “V”.

Types of Switches & Their Uses

There are numerous types of electronic switches available for countless applications. There are two main categories of electrical switches: mechanical and electronic. In the next two sections, we will take a closer look at these different types of switches and their applications.

Mechanical Switches

These are types of switches that require physical or manual contact with the switch - like moving, pressing, releasing, or touching - for operation. Mechanical switches are comprised of two metal plates (a.k.a., switch contacts) that touch each other to make a physical contact for the electrical current to flow, then they separate from each other to interrupt the flow of current. This performs the ON and OFF functions of the switch respectively.

Mechanical switches are mainly categorized by the number of poles and throws available to the device. Poles are the number of input circuits or power circuits available to the switch. The throws are the number of output circuits or paths available in which current can flow.

SPST (Single Pole Single Throw)

An SPST switch is a basic ON and OFF switch that consists of one input contact and one output contact. This switch is commonly used in homes for lighting circuits, small load appliances, computers, and similar electronic devices. SPST switches can power a single circuit by either making (ON) or breaking (OFF) the load.

SPDT (Single Pole Double Throw)

The SPDT switch has three terminals: one is the input contact (pole) and the remaining two are output contacts (throw), hence the name Single Pole Double Throw. Also commonly called a selector switch, the SPDT consists of two ON positions and one OFF position and can supply current or signal to two loops. So the switch is used as a changeover to connect the input between two choices of outputs in most circuits.

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DPST (Double Pole Single Throw)

The DPST is basically like two SPSTs in one that can operate simultaneously and is controlled by a single lever. A DPST switch consists of four terminals: two input contacts and two output contacts. Also, the output contacts may be either normally open or normally closed configurations. A DPST switch is commonly used for controlling two different circuits at a time.

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DPDT (Double Pole Double Throw)

The DPDT is like two separate SPDT configurations operating at the same time. It’s basically a  dual ON/OFF switch consisting of two ON positions. The DPDT switch consists of six terminals: two input terminals (poles) with two terminals for each pole for a total of four output terminals (throw). When operating a DPDT switch, the two input contacts are connected to one set of output contacts in one position, then connected to the other set of output contacts in another position.

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Rotary & Selector Switches

Rotary switches move in a circle with the ability to stop in several positions, and they are used to control different circuits with a single switch. Selector switches are rotary switches with a knob that rotates around an axis to switch and connect a common terminal to different output terminals. A selector switch is required when more than one control option is needed, for example, it requires to be turned on for a set time or when turned on it requires to be set on a specific option.

Intermediate Switch

An intermediate switch is an electric switch used to control a single electrical device from two locations. For example, when a staircase light can be controlled by both a switch at the top and a separate switch at the bottom. An intermediate switch uses four terminals to divert the flow of current from one position to another, and it's commonly called a 4-way switch.

Toggle Switch

A toggle switch is manually actuated or controlled by a mechanical handle, lever, or rocking mechanism, and they are most commonly used as light control switches. So this switch will remain stable in state until the lever is moved to another position. Toggle switches can fall into any of the mechanical categories we’ve previously mentioned, i.e., SPST, DPDT, DPST, DPDT, etc. With these switches, the ratings, sizes, and styles will vary depending on the circuit requirement and applications.

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Slide Switch

The slide switch, as the name indicates, uses a slider that moves back and forth to make and break the contacts. For example, an SPDT slide switch will control the flow of current in a circuit when it slides between the ON and OFF positions.

Push Buttons Switch

A push button switch is a momentary contact switch, meaning it uses a spring mechanism to close or open the circuit for OFF and ON operation. A doorbell is a common example of a push button switch.

Limit Switch

Limit switches have a bumper type of arm that is controlled or actuated by an object. So, when the bumper arm is manually pressed or comes into contact with an object that presses it (like a machine), it causes the switch contacts to change the position and operation of the circuit. Limit switches are commonly used in washing machines.

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Flow Switch

Flow switches are commonly used to detect the movement of liquid or air flow through a pipe or duct. The design varies depending on whether it's an air or liquid flow control situation. For example, with airflow, the switch uses a snap-action design where the switch is attached to a metal arm, which has a thin plastic or metal piece attached to it. When a large amount of air passes through this metal or plastic piece, it causes the movement of the metal arm, thereby operating the contacts of the switch.

Float Switch

Float switches are a type of contact liquid level sensor that uses a float to operate a switch. They are commonly used to control other devices such as alarms and pumps when a liquid level rises or falls to a specific point. For example, float switches are used to control DC and AC motor pumps by detecting the liquid or water level in a tank or sump.

Pressure Switch

Pressure switches are mechanical or electronic devices activated when the pressure of fluids, air, or gas reaches a specific threshold or setpoint, causing the contact to open or close and change the position of the system. These switches are commonly used in industrial applications to sense the pressure of hydraulic systems and pneumatic devices.

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Joystick Switch

A joystick switch consists of a lever that moves freely in more than one axis of motion, i.e., up, down, left, or right. With a joystick switch, the switch contacts are actuated or controlled depending on the movement of the stick. Joystick switches are most commonly used in gaming controller pads, building machinery, portable control equipment, camera motion control, trucks, excavators, and cranes.

Temperature & Thermal Switches

These switches operate on the principle of thermal expansion using a heat sensing element like a bimetallic strip that is bent when exposed to the heat. So, when the temperature rises and crosses a preset level, the bimetallic strip expands, breaks the contact, and opens the circuit.

Timer Switch

As the name suggests, a timer switch operates on a timing mechanism that turns a current load ON or OFF depending on the time settings.

Electronic Switches

Electronic switches are classified as solid state switches because there are no physical moving parts or physical contacts, they can be automatically operated by electric signals or programmed circuits like microcontrollers or microprocessors.

Electronic switches are constructed with semiconductor materials, and they are known for fast responses and accurate operations. They are also typically smaller in size and lower in cost than mechanical switches. Some types of electronic switches include transistors, SCRs, MOSFETs, TRIACs, and IGBTs. Next, we’ll explore these and other types of electrical switches and their applications.

Bipolar Transistor 

Transistors work like switches by either blocking a current or letting it pass. In this switching circuit, the current flows from the source, through the transistor to the load, then to the ground. So, if the base voltage is negative (i.e., ground or low), then the transistor is ON like a closed Switch. Alternatively, if the base voltage is positive (i.e., high), then the transistor is OFF like an open switch. 

Bipolar transistors are typically used in applications where speed is very important, such as in radio-frequency ICs. The bipolar transistor comes in two basic forms: an NPN (Negative-Positive-Negative) type and a PNP (Positive-Negative-Positive) type.

NPN Transistor

The NPN transistor is the most common type. They are three-terminal (see below), three-layer devices that can function as either electronic switches or amplifiers.
PNP Transistor

A PNP transistor also has three terminals – a collector, an emitter, and a base. The PNP transistor behaves like two positive-negative junction diodes connected back to back.

MOSFET

The MOSFET is one of the most common semiconductor switching devices. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor, and it is a unipolar and high-frequency switching device. It has three terminals: drain (output), source (common), and gate (input). The MOSFET is a voltage-controlled device. So when the input voltage is controlled, the resistance between the drain and source controls the ON and OFF state of the device. They are widely used for switching and amplifying electronic signals.

SCR

The SCR, a.k.a. Silicon Controlled Rectifier, is a four-layer solid-state current-controlling device consisting of three terminals: anode, cathode, and gate. An SCR switch is turned ON and OFF by controlling its gate input and biasing conditions of the anode and cathode terminals. SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium to high voltage AC power control applications, such as dimming a lamp, power regulators, and motor control.

IGBT

The IGBT, i.e., Insulated Gate Bipolar Transistor, is a voltage-controlled device (similar to MOSFET). The IGBT can be turned ON by applying a positive voltage that is greater than the threshold voltage between the gate and emitter. Subsequently, it can turn OFF by reducing the voltage across the gate-emitter to zero. Like the MOSFET, IGBTs are most commonly used with power electronic applications.

GTO

The GTO, or Gate Turn off Thyristor, is another bipolar semiconductor switching device that includes three terminals: an anode, a cathode, and a gate. A GTO is turned ON by applying a small positive gate current, which triggers the conduction mode. Subsequently, the GTO can turn OFF by a negative pulse to the gate. GTO switches are common for high-performance AC and DC motor drives.

DIAC

A DIAC, or Diode AC Switch, is a bidirectional switching device, which means it can be operated in either direction between two terminals. With the DIAC, when a voltage is applied, it either operates in forward blocking or reverse blocking mode - unless the applied voltage is less than the breakover voltage, at which point it begins conducting. DIACs are commomly used in the speed control of a universal motor or in a heat control circuit.

TRIAC

The Triac, or TRIode AC switch, is another bidirectional switching device capable of conducting current in both directions. It is mainly used for regulating power in AC circuits, the speed control of fans and motors, and dimmers in lamps and lights.

DIP

The DIP, or dual inline package, has multiple switches packed together in a compact size package. The electromechanical version is operated by manually moving the ON and OFF actuator, and the digital version automatically toggles the switch based on the input signals, which changes the operation of the circuit. The DIP is mainly used in breadboards and printed circuit boards (PCBs).

Relay

The relay controls high voltage circuits using a low voltage source. Basically, the relay creates an electromagnetic field around a coil, which then activates (energizes) the switch. Relays are used to control a circuit by an independent low-power signal, or where several circuits must be controlled by one signal. 

Since a relay completely isolates the low voltage circuit from the high voltage circuit, it can be used as a protective device. For example, a relay plays an important role in fault detection in power systems.

In summary, the different types of electronic switches available are many and vast. Acting as the control for electricity, switches are essential to our way of life.

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