Electric switches are devices that can open or close an electrical circuit. A majority of electric switches are binary devices that are either (1) closed to allow electrical current to pass through the circuit, or (2) open and unable to transmit current. Other types of electric switches have multiple closed positions that allow currents of varying voltages to pass through, which alters the output of the device or equipment to which the switch is attached.
The term circuit breaker is sometimes used as a synonym for an electric switch. This stems from the "open" status of a switch, in which an electrical circuit is physically altered or disrupted in order to "break" the circuit and prevent current flow. More accurately speaking, however, a circuit breaker is a safety-related accessory responsible for changing the switch to an "open"status when too much electrical current exists.
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The History of Electric Switches
Electric switches were invented out of necessity. Having an electrical current flow through a circuit is beneficial, but without a safe and easy way to stop and start it, the possibilities are limited. Switches introduced a new way of using electricity. Thus, the history of electric switches is intertwined with the overall discovery and history of electricity itself. Even though wall light switches are not the only type of electric switch, focusing on their development is helpful for getting an overall sense of how switches have progressed.
The first step toward the development of electric switches can arguably be traced back to 1800, when Italian scientist Alessandro Volta enabled the continuous flow of electrical current (i.e. electric circuits) with the first real battery (known as the voltaic pile). However, significant progress in the refinement and use of electric circuits did not occur until much later in the nineteenth century. Thomas Edison was at the forefront of developing electric lighting, which was the first common use of electric circuits for practical or commercial purposes. For a public New Year’s lighting display at his laboratory (1879-1880), Edison developed many innovative electrical components, including switches. Four years later, British engineer John Henry Holmes developed the quick break switch, which accelerated the meeting of electric contacts within a circuit and increased the overall durability of switches by preventing residue buildup. The quick break switch formed the basis of the next major development in switch technology - the toggle switch. Created by New York inventors William J. Newton and Morris Goldberg, the toggle switch came to replace push button switches that were popular in the latter nineteenth century. Strikingly, the toggle switch represents the majority of (North American) switches in use today.
Although electric switches have been improved since the first basic switches, the fundamental technology underlying them has not drastically changed. Compared to other forms of technology, electric switches are relatively simple. One example of twentieth-century switch development is the invention of the rocker switch, a version of the toggle switch intended for flat panels that appeared in the 1980s. In essence, however, the prototypical wall switch has remained largely unchanged for practically a century.
Components of Electric Switches
Switches generally consist of conducting material (e.g. wires), terminals and actuators housed in some sort of insulated, protective casing. These components vary widely in quantity and arrangement. Fundamentally speaking, however, most switches are similar in the sense that they use these components to complete a circuit by allowing an electrical current to flow through them.
How Electric Switches Work
As a topic, electric switches can only be properly understood within the general context of electric circuits. Two major types of electric circuits exist: power circuits and electric circuits. Power circuits denote the more "visible" types of electrical circuits which harness electricity en masse to power large physical systems or appliances. These types of systems are marked by features such as generators, power lines, and circuit breakers. Electronic circuits are far smaller systems responsible for transmitting various types of information via electricity. Computers and radar systems are representative of these types of circuits.
The term switching refers to the overall process of making or disrupting electrical connections in order to complete an electric circuit. Thus, the term electric switch can properly be applied to any piece within an electric circuit responsible for this function. Although switches are most commonly associated with mechanical pieces in commercial lighting systems, electronic or hydraulic pieces that perform switching functions would fall into the same category. Every electric switch possesses some conducting material in the form of electric "contacts." The switch either completes or disrupts a circuit by connecting or disconnecting these contacts. It is important to note that the terms open and closed have counter-intuitive meanings when applied to a switch. Instead of completing a circuit, an open switch "breaks" a circuit by somehow disconnecting the electric contacts; thus, the term open refers to the break, or "opening" in an electric circuit that stops electric current rather than enabling it. An open switch is normally described as being in the "off" position. Conversely, a closed switch completes an electric current by joining its electric contacts and allowing current to flow freely. Once again, the term closed stems from the actual configuration of the circuit rather than an abstract description of whether current can flow or not. A closed switch is also known as being in the "on" position.
While switches are often used on their own, they can be handled in a variety of ways. Switches can be connected to each other in order to increase the circuit options. Sometimes, switches are used in conjunction with other switches for more precise control of a circuit.
A key aspect of how a switch operates is its response to being actuated, or changed to a new state. When a switch remains in a new state after being newly actuated, it is known as a maintained switch. On the contrary, when a switch reverts back to its "own" state soon after being actuated, it is known as a momentary switch. The state a momentary switch is usually in (i.e. the state it stays in as long as it is not being actuated) is known as the switch’s normal state. Most normal states consist of an open/off position (although momentary switches usually in a closed/on position do exist). The contrast between toggle switches and push-button switches illustrate the contrast between these larger categories. As a maintained switch, a toggle wall switch will permanently stay in whatever state it is in until it is actuated into the other state; in contrast, push-button switches usually revert back to an "off" position after being actuated (e.g. a doorbell).
Although not typically considered part of a switch, receptacles are important features in electric switches that work in tandem with switches. Receptacles are simply parts of a power circuit responsible for actually conducting power to its intended target (e.g. a wall outlet). Since switches are mainly used to control and practically apply electricity within a circuit, receptacles are critical for switches to fulfill their intended use.
Types of Electric Switches
- Cam Switches
- Have a plastic disk (cam) over which contoured surface a mechanical follower moves, controlling the contacts. The cam is attached to and rotated by a handle shaft.
- DIP Switches
- Circuit boards with a packaged group of tiny electric switches. The set is called a dual in-line package and is used mainly in programmable electronic devices. DIP switches are very small manual binary switches and are an inexpensive way to customize an electronic device. A DIP switch consists of a circuit board with a packaged group of tiny electrical switches. The entire set is called a dual in-line package. These small, multi-switch banks are typically installed in devices like garage door openers and remote controls. They are valued for their ease of operation; flipping a switch turns on the component that coincides with that switch.
- Double Pole Switches
- Electric switches with a pair of actuators that are either connected or disconnected to a circuit. There are at least four terminals in a double pole (DP) switch and these common devices allow two circuits to be either on or off while controlled by a single actuator.
- Double Pole Double Throw (DPDT)
- Switches open or close the connections of two conductors to a pair of separate circuits. DPDT switches, which usually have six terminals, can be set to maintain contact, alternate contact or have momentary contact. A double pole switch is an electric switch with a pair of actuators that are either connected or disconnected to a circuit. Sometimes, double pole switches are able to attain a third type of position that disrupts all electrical contacts. Double pole switches are used to switch appliances using 240-volt circuits to a circuit of a different current. They are commonly used in devices with multiple mechanical parts that function simultaneously.
- Double Pole Single Throw (DPST)
- Switches open or close the connection of a pair of circuit conductors in a single circuit. DPST switches usually have four terminals.
- Electrical Switches
- Used for changing the flow of a circuit. Electrical switches may be categorized by various factors, such as the type of actuator they use. The actuator is the moving part that applies force to the contacts and may be a toggle, pushbutton, rocker or dial.
- Electronic Switches
- Devices that can interrupt the flow of a circuit. Many electronic switches are binary devices that are either closed to allow the current to pass through the circuit, or they are open, which breaks the flow.
- Enabling Switches
- Similar to safety switches, except they are manually operated. Enabling switches are designed to protect workers in more hazardous environments in which there is heavy machinery.
- Key Lock Switches
- Activated by use of a fitting key. The key is turned to one of several positions, triggering the switch. Key switches are used to power circuits in the same manner a car is started.
- Lever Switches
- Activated by turning a lever that is connected to a pivot point. Lever switches typically have three positions.
- Limit Switches
- Utilized in monitoring and for the control of machinery and industrial equipment. Limit switches come in many different sizes and configurations.
- Maintained Switches
- Stay in the selected position when the handle is released.
- Miniature Switches
- Used in applications that require compact mechanisms, such as handheld equipment.
- Multiple Limit Switches
- Used for the positioning and control of industrial equipment and machinery.
- Pressure Switches
- Convert pressure changes to electrical functions.
- Push Button Switches
- So called due to their activation method, which is usually in the form of a plunger that, when pushed down, opens or closes the switch. The configurations of these mechanical switches can be single-pole, single-throw (SPST), single-pole, double-throw (SPDT), double-pole, single throw (DPST), double-pole, double throw (DPDT) or solid state. Push button switches represent the most common type of momentary switches. These switches use a recessed, flush or raised button as the actuator. Some types of push button switches (e.g. doorbells) are also called leaf switches. Along with toggle switches, push button switches are some of the most common electric switch varieties. Latching buttons or switches are "maintained" versions of push button switches (e.g. stomp switches for guitars).
- Reed Switches
- Feature two contact blades, called ferromagnetic reeds, which are encapsulated in glass. The reeds close when exposed to a magnet. Reed switches are unique mechanical switches that operate based on the presence of a magnetic field; they are ideal for situations where physical contact for switch control is not preferable.
- Rocker Switches
- Electric switches that are activated by rocking the switch to one side. Rocker switches developed in the 1980s as a flat-paneled variation of the toggle switch. They move when pressed so that one end is raised while the other is depressed. They can be found on power strips and power locks in automobiles.
- Rope Pull Switches
- Triggered when there is tension in the safety cable. Rope pull switches provide safety and monitoring contacts in the printing, food processing and pharmaceutical industries.
- Rotary Switches
- Contacts that are arranged in a full or partial circle, which means the mechanism that selects the contact must be turned. Rotary switches, which may be manual or automatic, are used in such applications as automobile distributions or ignition switches. An example of an exception is a rotary switch, which is operated by rotating a control knob. Rotary switches are ideal for situations requiring multiple throws or conducting positions for a wide variety of output options. Dimmer switches, which can adjust household lighting to multiple shades within a lighting range, are good examples of a rotary switch.
- Safety Switches
- Feature integrated actuators, which serve to protect both equipment and personnel. This is done by monitoring the positions of movable components.
- Single Pole Switches
- Simple electric switches that are either connected or disconnected to a circuit. Single pole switches are general purpose switches that are used in many situations because they are either on or off, a useful and helpful characteristic. Single pole (SP) switches can be either single throw or double throw, which refers to the number of conducting positions, that is, the number of terminals that will complete the circuit.
- Single Pole Double Throw (SPDT)
- Also referred to as "three-way switches," open or close the connection of one conductor with one of two other conductors. SPDT switches often have three terminals and are sometimes used in pairs. Single pole/double throw (SPDT) switches are also called changeover switches because they enable a pair of output options within a single circuit. For example, a light able to turn on as green or red would be controlled by a SPDT switch. Many slide switches (which can slide in two different directions from a central position) would fall under this category.
- Single Pole Single Throw (SPST)
- Also called "single-pole switches," open or close the connection of one conductor in a single circuit. SPST switches usually have two terminals. Single pole/single-throw switches (SPST) are the simplest type of switch. They possess only one area for electrical input (a single pole) and can only connect to one another terminal (a single throw) in a certain position. Thus, they are used as general purpose "on/off" switches since they only offer two actuator positions.
- Slide Switches
- Devices that break an electrical circuit by moving linearly from position to position, interrupting the current’s flow. It is a common type of DIP (dual in-line package) switch and provides at least two switch positions including on or off. Slide switches break electrical circuits by moving linearly from position to position, interrupting the current's flow. They are distinguished by their sliding actuators and provide at least two switch positions, including "on" or "off". Flashlight buttons are a familiar representative of slide switches.
- Snap Action Switches
- Designed to very quickly move their contacts from one location to another. Mouse buttons and appliance settings use such switches.
- Switch Panels
- Allow users to quickly access a series of mounted electric switches that are arranged in an enclosure.
- Toggle Switches
- Have only two positions. Light switches and the caps lock key on a computer keyboard are examples of toggle switch applications. Toggle switches represent one of the earliest types of switches and the most common type of maintained switch. These switches use a lever, handle or rocker as an actuator and require a pushing or pulling motion. Toggle switches are ideal for quick switching, connecting and disconnecting in cases when the control devices are mounted very close to one another.
- Waterproof Switches
- Devices that can interrupt the flow of a circuit while operating in a wet environment. Waterproof switches are frequently binary; this means that they either close or open the circuit.
Usage of Electric Switches
Although switches may seem to be simple and basic to users today, they form critical parts of the electric circuits and corresponding devices on which much of the world has come to rely. Ultimately, electricity needs to be continuous and controllable for users to practically apply. Fortunately, circuits provide the former qualification while switches provide the latter. Two major applications of controlling electricity via switches are enabling binary "on/off" control (e.g. a remote control) or some form of user input (e.g. computer keys).
In addition, using electric switches helps to conserve energy because unused circuits can be shut off. Instead of having a device or appliance running constantly, they may be powered on only when in use due to the use of an electric switch.
By definition, an electric circuit is an enclosed path that enables the flow of electric current. Thus, an electric circuit must be composed of material that is able to permit the flow of electricity. In a majority of cases, electric circuits are created with conductive metal in the form of wires. The most common metals used in such cases are copper and aluminum. Gold is preferred in cases involving fragile electronic components (e.g. electronic chips) because of its strong corrosion resistance.
- Terminals of an Electric Circuit
- The terminals (or pins) of an electric circuit refer to the places in a circuit where current can (potentially) enter and exit. Minimally, a circuit requires two terminals, although the majority of circuits possess far more.
- Actuators on Switches
- When a switch is "actuated", it is changed from one state to another (e.g. closed to open) by some type of physical action. The actuators within a switch are the mechanisms responsible for performing such physical actions by applying force to the switch’s contacts.
- Insulators and Housing for Switches
- Insulators surround or enclose switches and circuits. As opposed to conductors, insulators consist of materials that do not transmit electricity (e.g. rubber or plastic). They are safety mechanisms that offset the presence of conducting material.
Powering an Electric Switch
Though all electrical switches are used to open or close electrical circuits, there are many different kinds of electronic switches. A single example illustrating switch variety concerns their size. Some switches are very small and necessitate a miniature tool to operate; some can be flipped with a finger while others require a strong hand. Accordingly, electric switches are identified by a variety of factors, such as the number of connections they can establish, how much voltage or current they can carry, etc. Power switches and signal switches are terms used to distinguish between switches attached to power circuits and those attached to electronic circuits. Load-break switches are representative power switches which exist in systems with high voltage; they often work together with devices known as interrupters that convert direct current (DC) into changing or alternating current (AC). The combination of a load-break switch (or another type of disconnect switch) and an interrupting device is sometimes called an interrupter switch.
The most useful way for categorizing switches, however, is by how a switch is controlled or actuated. Generally speaking, switches are either mechanically or physically controlled, or they are electronically controlled. Electric switches vary widely in terms of their control mechanism’s complexity; some complex switches are able to sense a light or magnetic field and react accordingly, while simpler switches require physical contact between the conductors and actuator. The most common forms of electric switch control include manual methods, pneumatic or hydraulic methods, or remote methods.
- Mechanically Controlled Switches
- Since mechanically controlled switches are extremely practicable, a very broad range of types exists. Pull-chain switches resemble the mechanisms used to start ceiling fans and require pulling some type of cord. Sometimes, a manually controlled switch may not be categorized by its method of control. For example, waterproof switches comprise a special category of switches enclosed in a watertight housing that is able to resist corrosion, salt, shock, vibrations and other potentially harmful forces.
- Electrically Controlled Switches
- Electronic circuits use switching devices that usually look very different from a prototypical wall switch. In electronic circuits, switches typically function invisibly at the level of minute electrical components. Switches within these circuits are often called signal switches because they function by adjusting a circuit based on their interpretation of surrounding conditions. Electronic input based on these conditions is responsible for moving contacts within the switch and opening or closing the circuit (rather than an external, physical intervention). More specifically, applications of certain electric voltages are responsible for moving contacts within the switch. The term switch relay can be applied to any switch that is electronically controlled.
- Although mechanical switches are very common, semiconductor transistors represent the true majority of electric switches today. The irony of transistors lies in the fact that they are used to control electrical circuits when the transistors themselves are controlled by a smaller electric current. Transistors are obviously critical components of the computing industry. A more visible form of an electronically controlled switch is a remote electrical switch, which is used for applications such as internal lighting control. Familiar products that use electric signal switches include driving lights/indicators, thermostats (which respond to temperature levels) and security lights (which respond to natural light levels). Additional devices usually equipped with electronic switches include food processing and medical equipment. Many future trends in the electric switch industry are focused on electronically controlled switches. Some related examples include touch switches and waving switches.
- Poles and Throws Switches
- Electronic switches are also categorized according to the arrangement of internal components. These categorizations revolve around the concept of poles and throws. The term pole refers to an area on a switch that can accept electrical input and, accordingly, the number of circuits that switch can control. The term throw refers to any conducting position that switch’s pole can be placed in, or the number of terminals that will complete the circuit. Switches are often classified as a single/double pole switch as well as a single/double throw switch, thus creating four common combinations abbreviated as SPST, SPDT, DPST, and DPDT.
- Switches can be designed with any number of poles and throws, although the single/double varieties are by far the most common.
Switches can be customized in a variety of ways beyond their method of control or internal arrangement.
When many switches are installed in a single device, that device is often referred to as a switch panel. Manufacturers of switch panels can make them so that they are composed of several single pole, double pole and other kinds of switches and so that they can be used to control multiple electronic circuits. The wires, terminals and other components are hidden within the plastic, metal or wooden housing, while the switches themselves are mounted on the panel's face.
In terms of size, smaller components allow switches to be downsized and to fit in tighter spaces. They do not require much space, and sometimes the entire electronic device with which the switch is used can be made in a smaller size.
Better materials and finer machining allow for high quality parts and components that do not wear out as quickly and that can provide the same service for hundreds if not thousands of repetitions during the switches' lifetime. These switches can be used in demanding environments where their functionality is critical.
Choosing and Maintaining Electric Switches
A recurring theme among electric switches is their high importance (for the functioning of an electric circuit), despite their relative simplicity (with regard to their basic operation). Thus, it is important to avoid sloppiness when selecting electrical switchgear or related products. Switches vary widely in quality as well as in design and specific function. As a general rule, it is wiser to invest greater financial resources in high-quality, durable switches (and related accessories, such as receptacles). It is important to select a manufacturer or other supplier of electric switch services that is reputable as well as capable and willing to find a quality switch for your specific application(s).
Since electric switches are the most critical components of any electric circuit, they must also be handled and maintained with great care. Switches can fail (often more frequently than expected) due to broken internal components from heavy usage or unexpected shocks. Recommended practices include regularly testing switches (e.g. with a battery-operated continuity tester) and immediately replacing faulty or corrupt switches. You should never disregard or violate any safety precautions regarding switch usage; examples include exceeding the maximum current capacity for a particular switch (e.g. using a simple SPDT slide switch for a hundred-plus device power circuit), or using receptacles designed for different amperages/voltages on the circuit your switch controls.
Electric Switches Terms
- A mechanism that puts something into automatic action. In electrical switch terms, actuators include plungers, plain levers, simulated roller levers and many other examples.
- Alternating Current (AC)
- An electrical current that intermittently changes direction of flow.
- Ampere-Turns (AT)
- A unit of measurement that is used to define switch sensitivity. AT is calculated by the number of turns of the coil in which the switch is tested and the current (expressed in amps) that flows through the coil.
- The opening of a circuit, the act of which prohibits current flow.
- A closed path along which an electric current flows.
- A mechanism consisting of a spring and starwheel that holds a switch in a specified position.
- Direct Current (DC)
- An electric current that flows in only one direction.
- Drop-Out (DO)
- The point at which the switch contacts simply release, expressed in ampere-turns.
- The part of an electric circuit connected to the earth that has a zero potential. Most electric switches have ground connections.
- The ability of a relay to have its contacts opened or closed upon command and remain in that position until another command is given.
- The closing of a contact, the act of which permits current flow.
- Maximum Switching Current
- The maximum load, referred to as amperage, that an electric switch is capable of carrying.
- Normally Closed (NC)
- A term that refers to a switch that is closed and connected in its normal position.
- Normally Open (NO)
- A term that refers to a switch that is open and disconnected in its normal position.
- Plain Lever
- A small rigid bar that is attached to a pivot point and is activated by being pushed one way or another. Lever switches normally have two or three positions.
- A type of actuator that is activated with a push or thrust.
- An independent electrical circuit of a switch.
- Set Point
- The specific point at which an element of an electrical switch functions, expressed in psi, psia or inches of mercury.
- The position in a circuit at which a connection is normally established or broken.
- A plastic material that can be heated and expanded as well as cooled and stiffened without any significant chemical change. Thermoplastics serve as dedicated housing to some switches.
- A specified performance limit given to switches. Volts (V) and amperes (amps) are the standard units for establishing ratings.