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electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, a switch is an
electrical component An electronic component is any basic discrete electronic device or physical entity part of an Electronics, electronic system used to affect electrons or their associated electromagnetic field, fields. Electronic components are mostly industrial ...
that can disconnect or connect the conducting path in an
electrical circuit An electrical network is an interconnection of electrical components (e.g., battery (electricity), batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e. ...
, interrupting the
electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
or diverting it from one conductor to another. The most common type of switch is an electromechanical device consisting of one or more sets of movable
electrical contact An electrical contact is an Electronic component, electrical circuit component found in electrical switches, relays, Electrical connector, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically meta ...
s connected to external circuits. When a pair of contacts is touching current can pass between them, while when the contacts are separated no current can flow. Switches are made in many different configurations; they may have multiple sets of contacts controlled by the same knob or actuator, and the contacts may operate simultaneously, sequentially, or alternately. A switch may be operated manually, for example, a
light switch In electrical wiring, a light switch is a switch most commonly used to operate electric lights, permanently connected equipment, or AC power plugs and sockets, electrical outlets. Portable lamps such as table lamps may have a light switch mounte ...
or a keyboard button, or may function as a sensing element to sense the position of a machine part, liquid level, pressure, or temperature, such as a
thermostat A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint. Thermostats are used in any device or system tha ...
. Many specialized forms exist, such as the
toggle switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...
,
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". A rotary switch consists of a spi ...
,
mercury switch A mercury switch is an electricity, electrical switch that opens and closes a electrical circuit, circuit when a small amount of the liquid metal mercury (element), mercury connects metal electrodes to close the circuit. There are several differ ...
,
push-button A push-button (also spelled pushbutton) or simply button is a simple switch mechanism to control some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or sh ...
switch,
reversing switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...
,
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
, and
circuit breaker A circuit breaker is an electrical safety device designed to protect an Electrical network, electrical circuit from damage caused by current in excess of that which the equipment can safely carry (overcurrent). Its basic function is to interr ...
. A common use is control of lighting, where multiple switches may be wired into one circuit to allow convenient control of light fixtures. Switches in high-powered circuits must have special construction to prevent destructive arcing when they are opened.


Description

The most familiar form of switch is a manually operated electromechanical device with one or more sets of
electrical contacts An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they ...
, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) is usually (there are other types of actions) either an "''alternate action''" (flip the switch for continuous "on" or "off") or "''momentary''" (push for "on" and release for "off") type. A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a
light switch In electrical wiring, a light switch is a switch most commonly used to operate electric lights, permanently connected equipment, or AC power plugs and sockets, electrical outlets. Portable lamps such as table lamps may have a light switch mounte ...
. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another workpiece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting as
sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...
s in a process and used to automatically control a system. For example, a
thermostat A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint. Thermostats are used in any device or system tha ...
is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be padlocked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock. An ideal switch would have no voltage drop when closed, and would have no limits on voltage or current rating. It would have zero
rise time In electronics, when describing a voltage or current step function, rise time is the time taken by a signal to change from a specified low value to a specified high value. These values may be expressed as ratiosSee for example , and . or, equiva ...
and
fall time In electronics, fall time (pulse decay time) t_f is the time taken for the amplitude of a pulse to decrease (fall) from a specified value (usually 90% of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 ...
during state changes, and would change state without "bouncing" between on and off positions. Practical switches fall short of this ideal; as the result of roughness and oxide films, they exhibit
contact resistance Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting sur ...
, limits on the current and voltage they can handle, finite switching time, etc. The ideal switch is often used in circuit analysis as it greatly simplifies the system of equations to be solved, but this can lead to a less accurate solution. Theoretical treatment of the effects of non-ideal properties is required in the design of large networks of switches, as for example used in telephone exchanges.


Contacts

In the simplest case, a switch has two conductive pieces, often
metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
, called ''contacts'', connected to an external circuit, that touch to complete (make) the circuit, and separate to open (break) the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Contact materials are also chosen on the basis of
electrical conductivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...
, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity. The formation of oxide layers at contact surface, as well as surface roughness and contact pressure, determine the
contact resistance Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting sur ...
, and
wetting current In electrical and electronics engineering, wetting current is the minimum electric current needing to flow through a contact to break through the surface film resistance at a contact. It is typically far below the contact's nominal maximum curre ...
of a mechanical switch. Sometimes the contacts are
plated Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderab ...
with
noble metal A noble metal is ordinarily regarded as a metallic chemical element, element that is generally resistant to corrosion and is usually found in nature in its native element, raw form. Gold, platinum, and the other platinum group metals (ruthenium ...
s, for their excellent conductivity and resistance to corrosion. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design.


Contact terminology

In electronics, switches are classified according to the arrangement of their contacts. A pair of contacts is said to be "''closed''" when current can flow from one to the other. When the contacts are separated by an insulating air gap, they are said to be "''open''", and no current can flow between them at normal voltages. The terms "''make''" for closure of contacts and "''break''" for opening of contacts are also widely used. The terms pole and throw are also used to describe switch contact variations. The number of "''poles''" is the number of electrically separate switches which are controlled by a single physical actuator. For example, a "''2-pole''" switch has two separate, parallel sets of contacts that open and close in unison via the same mechanism. The number of "''throws''" is the number of separate wiring path choices other than "open" that the switch can adopt for each pole. A single-throw switch has one pair of contacts that can either be closed or open. A double-throw switch has a contact that can be connected to either of two other contacts, a triple-throw has a contact which can be connected to one of three other contacts, etc. In a switch where the contacts remain in one state unless actuated, such as a
push-button A push-button (also spelled pushbutton) or simply button is a simple switch mechanism to control some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or sh ...
switch, the contacts can either be normally open (abbreviated "n.o." or "no") until closed by operation of the switch, or normally closed ("n.c." or "nc") and opened by the switch action. A switch with both types of contact is called a ''changeover switch'' or ''double-throw switch''. These may be "make-before-break" ("MBB" or shorting) which momentarily connects both circuits, or may be "break-before-make" ("BBM" or non-shorting) which interrupts one circuit before closing the other. These terms have given rise to abbreviations for the types of switch which are used in the
electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...
industry such as "''single-pole, single-throw''" (SPST) (the simplest type, "on or off") or "''single-pole, double-throw''" (SPDT), connecting either of two terminals to the common terminal. In
electrical power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...
wiring (i.e., house and building wiring by
electrician An electrician is a tradesman, tradesperson specializing in electrical wiring of buildings, transmission lines, stationary machines, and related equipment. Electricians may be employed in the installation of new electrical components or the ...
s), names generally involve the suffix ''"-way"''; however, these terms differ between
British English British English is the set of Variety (linguistics), varieties of the English language native to the United Kingdom, especially Great Britain. More narrowly, it can refer specifically to the English language in England, or, more broadly, to ...
and
American English American English, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lang ...
(i.e., the terms ''two way'' and ''three way'' are used with different meanings). Switches with larger numbers of poles or throws can be described by replacing the "S" or "D" with a number (e.g. 3PST, SP4T, etc.) or in some cases the letter "T" (for "triple") or "Q" (for "quadruple"). In the rest of this article the terms ''SPST'', ''SPDT'' and ''intermediate'' will be used to avoid the ambiguity.


Contact bounce


Bounce

Contact bounce (also called ''chatter'') is a common problem with mechanical switches,
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
s and
battery contact An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negati ...
s, which arises as the result of electrical
contact resistance Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting sur ...
(ECR) phenomena at interfaces. Switch and relay contacts are usually made of springy metals. When the contacts strike together, their momentum and elasticity act together to cause them to bounce apart one or more times before making steady contact. The result is a rapidly pulsed electric current instead of a clean transition from zero to full current. The effect is usually unimportant in power circuits, but causes problems in some analogue and
logic circuit A logic gate is a device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has, for ...
s that respond fast enough to misinterpret the on‑off pulses as a data stream.Walker, PMB, ''Chambers Science and Technology Dictionary'', Edinburgh, 1988, In the design of micro-contacts, controlling surface structure (
surface roughness Surface roughness or simply roughness is the quality of a surface of not being smooth and it is hence linked to human ( haptic) perception of the surface texture. From a mathematical perspective it is related to the spatial variability structure ...
) and minimizing the formation of passivated layers on metallic surfaces are instrumental in inhibiting chatter. In the
Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert, first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, sound was created ...
, multiple wires are pressed together under the piano keys of the manuals. Their bouncing and non-synchronous closing of the switches is known as ''Hammond Click'' and compositions exist that use and emphasize this feature. Some
electronic organ An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the pump organ, harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has si ...
s have a switchable replica of this sound effect.


Debouncing

The effects of contact bounce can be eliminated by: * Use of Mercury-wetted relay, mercury-wetted contacts, but these are now infrequently used because of the hazards of mercury. * Alternatively, contact circuit voltages can be low-pass filtered to reduce or eliminate multiple pulses from appearing. * In digital systems, multiple samples of the contact state can be taken at a low rate and examined for a steady sequence, so that contacts can settle before the contact level is considered reliable and acted upon. See . * Bounce in #Contact terminology, SPDT ("single-pole, double-throw") switch contacts signals can be filtered out using an Multivibrator#Bistable, SR flip-flop (latch) or Schmitt trigger. All of these methods are referred to as 'debouncing'.


Arcs and quenching

When the power being switched is sufficiently large, the electron flow across opening switch contacts is sufficient to ionize the air molecules across the tiny gap between the contacts as the switch is opened, forming a gas plasma, also known as an electric arc. The plasma is of low resistance and is able to sustain power flow, even with the separation distance between the switch contacts steadily increasing. The plasma is also very hot and is capable of eroding the metal surfaces of the switch contacts (the same true for vacuum switches). Electric current arcing causes significant Contact protection#Contact wear, degradation of the contacts and also significant electromagnetic interference (EMI), requiring the use of arc suppression methods. Where the voltage is sufficiently high, an arc can also form as the switch is closed and the contacts approach. If the voltage potential is sufficient to exceed the breakdown voltage of the air separating the contacts, an arc forms which is sustained until the switch closes completely and the switch surfaces make contact. In either case, the standard method for minimizing arc formation and preventing contact damage is to use a fast-moving switch mechanism, typically using a spring-operated Tipping point (physics), tipping-point mechanism to assure quick motion of switch contacts, regardless of the speed at which the switch control is operated by the user. Movement of the switch control lever applies tension to a spring until a tipping point is reached, and the contacts suddenly snap open or closed as the spring tension is released. As the power being switched increases, other methods are used to minimize or prevent arc formation. A plasma is hot and will rise due to convection air currents. The arc can be quenched with a series of non-conductive blades spanning the distance between switch contacts, and as the arc rises, its length increases as it forms ridges rising into the spaces between the blades, until the arc is too long to stay sustained and is extinguished. A ''puffer'' may be used to blow a sudden high velocity burst of gas across the switch contacts, which rapidly extends the length of the arc to extinguish it quickly. Extremely large switches often have switch contacts surrounded by something other than air to more rapidly extinguish the arc. For example, the switch contacts may operate in a vacuum, immersed in mineral oil, or in Sulfur hexafluoride#Dielectric medium, sulfur hexafluoride. In AC power service, the current periodically passes through zero; this effect makes it harder to sustain an arc on opening. Manufacturers may rate switches with lower voltage or current rating when used in DC circuits.


Power switching

When a switch is designed to switch significant power, the transitional state of the switch as well as the ability to withstand continuous operating currents must be considered. When a switch is in the on state, its resistance is near zero and very little power is dropped in the contacts; when a switch is in the off state, its resistance is extremely high and even less power is dropped in the contacts. However, when the switch is flicked, the resistance must pass through a state where a quarter of the load's rated power (or worse if the load is not purely resistive) is briefly dropped in the switch. For this reason, power switches intended to interrupt a load current have spring mechanisms to make sure the transition between on and off is as short as possible regardless of the speed at which the user moves the rocker. Power switches usually come in two types. A momentary on‑off switch (such as on a laser pointer) usually takes the form of a button and only closes the circuit when the button is depressed. A regular on‑off switch (such as on a flashlight) has a constant on-off feature. Dual-action switches incorporate both of these features.


Inductive loads

When a strongly inductance, inductive load such as an electric motor is switched off, the current cannot drop instantaneously to zero; a Electric arc, spark will jump across the opening contacts. Switches for inductance, inductive loads must be rated to handle these cases. The spark will cause electromagnetic interference if not suppressed; a snubber network of a resistor and capacitor in series will quell the spark.


Incandescent loads

When turned on, an Incandescent light bulb, incandescent lamp draws a large inrush current of about ten times the steady-state current; as the filament heats up, its resistance rises and the current decreases to a steady-state value. A switch designed for an incandescent lamp load can withstand this inrush current.


Wetting current

''Wetting current'' is the minimum current needing to flow through a mechanical switch while it is operated to break through any film of oxidation that may have been deposited on the switch contacts. The film of oxidation occurs often in areas with high humidity. Providing a sufficient amount of wetting current is a crucial step in designing Control engineering, systems that use delicate switches with small contact pressure as sensor inputs. Failing to do this might result in switches remaining electrically "open" due to contact oxidation.


Actuator

The moving part that applies the operating force to the contacts is called the ''actuator'', and may be a toggle or ''dolly'', a rocker, a push-button or any type of mechanical linkage ''(see photo).''


Biased switches

A switch normally maintains its set position once operated. A biased switch contains a mechanism that springs it into another position when released by an operator. The momentary
push-button A push-button (also spelled pushbutton) or simply button is a simple switch mechanism to control some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or sh ...
switch is a type of biased switch. The most common type is a "push-to-make" (or normally-open or NO) switch, which makes contact when the button is pressed and breaks when the button is released. Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released. An example of a push-to-break switch is a button used to release a door held closed by an electromagnet. The interior lamp of a household refrigerator is controlled by a switch that is held open when the door is closed.


Rotary switch

A rotary switch operates with a twisting motion of the operating handle with at least two positions. One or more positions of the switch may be momentary (biased with a spring), requiring the operator to hold the switch in the position. Other positions may have a detent to hold the position when released. A rotary switch may have multiple levels or "decks" in order to allow it to control multiple circuits. One form of rotary switch consists of a spindle or "rotor" that has a contact arm or "spoke" which projects from its surface like a cam. It has an array of terminals, arranged in a circle around the rotor, each of which serves as a contact for the "spoke" through which any one of a number of different electrical circuits can be connected to the rotor. The switch is layered to allow the use of multiple poles, each layer is equivalent to one pole. Usually such a switch has a detent mechanism so it "clicks" from one active position to another rather than stalls in an intermediate position. Thus a rotary switch provides greater pole and throw capabilities than simpler switches do. Other types use a cam mechanism to operate multiple independent sets of contacts. Rotary switches were used as channel selectors on television receivers until the early 1970s, as range selectors on electrical metering equipment, as band selectors on multi-band radios and other similar purposes. In industry, rotary switches are used for control of measuring instruments, switchgear, or in control circuits. For example, a radio controlled overhead crane may have a large multi-circuit rotary switch to transfer hard-wired control signals from the local manual controls in the cab to the outputs of the remote control receiver.


Toggle switch

A toggle switch or tumbler switch is a class of electrical switches that are manually actuated by a mechanical lever, handle, or rocking mechanism. Toggle switches are available in many different styles and sizes, and are used in numerous applications. Many are designed to provide the simultaneous actuation of multiple sets of
electrical contact An electrical contact is an Electronic component, electrical circuit component found in electrical switches, relays, Electrical connector, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically meta ...
s, or the control of large amounts of
electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
or Mains electricity, mains voltages. The word "toggle" is a reference to a kind of mechanism or joint consisting of two arms, which are almost in line with each other, connected with an elbow-like pivot. However, the phrase "toggle switch" is applied to a switch with a short handle and a positive snap-action, whether it actually contains a toggle mechanism or not. Similarly, a switch where a definitive click is heard, is called a "positive on-off switch". A very common use of this type of switch is to switch lights or other electrical equipment on or off. Multiple toggle switches may be mechanically interlocked to prevent forbidden combinations. In some contexts, particularly computing, a toggle switch, or the action of toggling, is understood in the different sense of a mechanical or software switch that alternates between two states each time it is activated, regardless of mechanical construction. For example, the caps lock key on a computer causes all letters to be generated in capitals after it is pressed once; pressing it again reverts to lower-case letters.


Special types

Switches can be designed to respond to any type of mechanical stimulus: for example, vibration (the trembler switch), tilt, air pressure, fluid level (a float switch), the turning of a key (key switch), linear or rotary movement (a limit switch or microswitch), or presence of a magnetic field (the reed switch). Many switches are operated automatically by changes in some environmental condition or by motion of machinery. A limit switch is used, for example, in machine tools to interlock operation with the proper position of tools. In heating or cooling systems a sail switch ensures that air flow is adequate in a duct. Pressure switches respond to fluid pressure.


Mercury tilt switch

The mercury switch consists of a drop of mercury (element), mercury inside a glass bulb with two or more contacts. The two contacts pass through the glass, and are connected by the mercury when the bulb is tilted to make the mercury roll on to them. This type of switch performs much better than the ball tilt switch, as the liquid metal connection is unaffected by dirt, debris and oxidation, it wets the contacts ensuring a very low resistance bounce-free connection, and movement and vibration do not produce a poor contact. These types can be used for precision works. It can also be used where arcing is dangerous (such as in the presence of explosive vapour) as the entire unit is sealed.


Knife switch

Knife switches consist of a flat metal blade, hinged at one end, with an insulating handle for operation, and a fixed contact. When the switch is closed, current flows through the hinged pivot and blade and through the fixed contact. Such switches are usually not enclosed. The knife and contacts are typically formed of copper, steel, or brass, depending on the application. Fixed contacts may be backed up with a spring. Several parallel blades can be operated at the same time by one handle. The parts may be mounted on an insulating base with terminals for wiring, or may be directly bolted to an insulated switch board in a large assembly. Since the electrical contacts are exposed, the switch is used only where people cannot accidentally come in contact with the switch or where the voltage is so low as to not present a hazard. Knife switches are made in many sizes from miniature switches to large devices used to carry thousands of amperes. In electrical transmission and distribution, gang-operated switches are used in circuits up to the highest voltages. The disadvantages of the knife switch are the slow opening speed and the proximity of the operator to exposed live parts. Metal-enclosed safety disconnect switches are used for isolation of circuits in industrial power distribution. Sometimes spring-loaded auxiliary blades are fitted which momentarily carry the full current during opening, then quickly part to rapidly extinguish the arc.


Reversing switch

A DPDT switch has six connections, but since polarity reversal is a very common usage of DPDT switches, some variations of the DPDT switch are internally wired specifically for polarity reversal. These crossover switches only have four terminals rather than six. Two of the terminals are inputs and two are outputs. When connected to a battery or other DC source, the 4-way switch selects from either normal or reversed polarity. Such switches can also be used as intermediate switches in a multiway switching system for control of lamps by more than two switches.


Light switches

In building wiring, light switches are installed at convenient locations to control lighting and occasionally other circuits. By use of multiple-pole switches, multiway switching control of a lamp can be obtained from two or more places, such as the ends of a corridor or stairwell. A wireless light switch allows remote control of lamps for convenience; some lamps include a touch switch which electronically controls the lamp if touched anywhere. In public buildings several types of vandal resistant switches are used to prevent unauthorized use.


Slide switches

Slide switches are mechanical switches using a slider that moves (slides) from the open (off) position to the closed (on) position.


Electronic switches

The term ''switch'' has since spread to a variety of solid state electronics that perform a switching function, but which are controlled electronically by active devices rather than purely mechanically. These are categorized in the article electronic switch. Electromechanical switches (such as the traditional
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
, Crossbar Switch#Electromechanical switching in telephony, electromechanical crossbar, and Strowger switch) bridge the categorization.


Other switches

* Centrifugal switch * Company switch * Crossbar switch * Dead man's switch * Fireman's switch * Hall-effect switch * Inertial switch * Isolator switch * Key switch * Kill switch * Latching switch * Light switch * Load control switch * Membrane switch * MEMS switch * Optical switch * Piezo switch * Pull switch * Push switch * Sense switch * Slotted optical switch * Stepping switch * Strowger switch * Thermal switch * Time switch * Touch switch * Transfer switch * Zero speed switch


See also

* Circuit breaker * Commutator (electric) * Contact resistance * DIN rail * Electric switchboard * Fuse cutout * RF switch matrix * Switch access * Switchgear


Notes


References


External links

* {{Authority control Switches, Electrical components Human–machine interaction