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123-422: 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 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

246-430: A chain reaction . Rapidly the insulator becomes filled with mobile charge carriers, and its resistance drops to a low level. In a solid, the breakdown voltage is proportional to the band gap energy. When corona discharge occurs, the air in a region around a high-voltage conductor can break down and ionise without a catastrophic increase in current. However, if the region of air breakdown extends to another conductor at

369-407: 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. When a strongly inductive load such as an electric motor is switched off, the current cannot drop instantaneously to zero; a spark will jump across

492-460: A multiway switching system for control of lamps by more than two 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

615-500: 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. 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

738-417: A sail switch ensures that air flow is adequate in a duct. Pressure switches respond to fluid pressure. The mercury switch consists of a drop of 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

861-473: A thermostat . Many specialized forms exist, such as the toggle switch , rotary switch , mercury switch , push-button switch, reversing switch , relay , and circuit breaker . 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. The most familiar form of switch

984-410: 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. Light switch In electrical wiring , a light switch is a switch most commonly used to operate electric lights , permanently connected equipment, or electrical outlets . Portable lamps such as table lamps may have

1107-468: 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

1230-568: A central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or ethylene propylene diene monomer rubber ( EPDM ). Composite insulators are less costly, lighter in weight, and have excellent hydrophobic properties. This combination makes them ideal for service in polluted areas. However, these materials do not yet have the long-term proven service life of glass and porcelain. The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways: Most high voltage insulators are designed with

1353-441: A compression spring into a notch in the common contact bar. The common contact bar is free to rock on a small diameter rod, welded to the common terminal. However, because of the pressure applied by the compression spring, the common contact bar will always be held against one of the two contacts. When the actuator is moved, mechanical energy is stored in the compression spring until the actuator passes its mid-position. At that time,

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1476-497: A conductor, causing a large increase in current, an electric arc through the substance. Electrical breakdown occurs when the electric field in the material is strong enough to accelerate free charge carriers (electrons and ions, which are always present at low concentrations) to a high enough velocity to knock electrons from atoms when they strike them, ionizing the atoms. These freed electrons and ions are in turn accelerated and strike other atoms, creating more charge carriers, in

1599-506: A conductor, such as a metal , if an electric potential difference is applied to the material. If no such states are available, the material is an insulator. Most insulators have a large band gap . This occurs because the "valence" band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage (called the breakdown voltage ) that gives electrons enough energy to be excited into this band. Once this voltage

1722-429: 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 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

1845-410: A different voltage it creates a conductive path between them, and a large current flows through the air, creating an electric arc . Even a vacuum can suffer a sort of breakdown, but in this case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself. In addition, all insulators become conductors at very high temperatures as

1968-445: 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

2091-408: A full-length of bottom-contact third rail . Pin-type insulators are unsuitable for voltages greater than about 69 kV line-to-line. Higher voltage transmission lines usually use modular suspension insulator designs. The wires are suspended from a 'string' of identical disc-shaped insulators that attach to each other with metal clevis pin or ball-and-socket links. The advantage of this design

2214-562: A given switch design. 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 "

2337-481: A good balance of economy and adequate performance. Busbars and circuit breakers in switchgear may be insulated with glass-reinforced plastic insulation, treated to have low flame spread and to prevent tracking of current across the material. In older apparatus made up to the early 1970s, boards made of compressed asbestos may be found; while this is an adequate insulator at power frequencies, handling or repairs to asbestos material can release dangerous fibers into

2460-448: A hand-held transmitter. While the controlling device may be a unit dedicated to this purpose, increasingly such switches may be controlled by the technology (such as Bluetooth or Wi-Fi ) now found in smartphones . Wired remote control of lighting switches is also possible using, for example, X10 signaling over the power wires. Two or more light switches can be interconnected to allow control of lighting from, for example, two ends of

2583-700: A heating process. A switch that is operated by another electrical circuit is called a relay . 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 and fall time during state changes, and would change state without "bouncing" between on and off positions. Practical switches fall short of this ideal; as

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2706-414: A key to operate and so discourage casual or accidental operation of the switch. In North American commercial and industrial lighting installations, lighting installed on 480Y/277 V 3-phase circuits uses voltages higher than the rating of common 120 V switches. Around the middle of the 20th century, "quiet" switches were introduced that used mercury to make the connection, avoiding the loud snap made by

2829-499: A light socket is sometimes installed in basement or utility areas of homes. The switch is operated by a pull chain or cord. It is also possible to have the cord-operated switch separate from the light socket, which is particularly common in British bathrooms. Until 2001, UK wiring regulations required that all bathroom switches were operated by pull cords. Also called foot switch. It is a type of switch for tall floor lamps, mounted on

2952-464: A light switch mounted on the socket, base, or in-line with the cord. Manually operated on/off switches may be substituted by dimmer switches that allow controlling the brightness of lamps as well as turning them on or off, time-controlled switches, occupancy-sensing switches, and remotely controlled switches and dimmers. Light switches are also found in flashlights , vehicles , and other devices. The first light switch employing "quick-break technology"

3075-460: A load of 80–120 kilonewtons (18,000–27,000  lb f ), have a dry flashover voltage of about 72 kV, and are rated at an operating voltage of 10–12 kV. However, the flashover voltage of a string is less than the sum of its component discs, because the electric field is not distributed evenly across the string but is strongest at the disc nearest to the conductor, which flashes over first. Metal grading rings are sometimes added around

3198-992: A long hallway or landings at the upper and lower landings of a flight of stairs. Multiway switching is done using special switches that have additional contacts. Earlier switches were made of porcelain in the surface-mounted version and operated as a rotary switch with a rotary mechanism. Later, more durable Bakelite and Ebonite was used. Today they are made of modern plastics , like Polycarbonate or fire resistant ABS. Some switches may also be manufactured from other plastics like polyamide, polypropylene or pvc but mainly limited to wire mounted switches (like night lamp switches) mainly due to reduced weight, and most such switches are not used in high power devices (mainly table lamps, table fans, some radios) mainly up to 2 amperes. In some cases, especially in hospitals and other public facilities, exposed parts of light switches are made of antimicrobial materials such as copper , for infection control . Insulator (electric) An electrical insulator

3321-422: A lower flashover voltage than puncture voltage, so they flash over before they puncture, to avoid damage. Dirt, pollution, salt, and particularly water on the surface of a high voltage insulator can create a conductive path across it, causing leakage currents and flashovers. The flashover voltage can be reduced by more than 50% when the insulator is wet. High voltage insulators for outdoor use are shaped to maximise

3444-517: A manual switch. In these systems light switches control lighting contactors , a relay that allows the manual light switch to operate on a lower current, with smaller wiring than would be required in the main lighting circuit. In the UK, putting 13 amp BS 1363 sockets on a lighting circuit is discouraged (although not outright prohibited), but 2 amp or 5 amp BS 546 outlets are often put on lighting circuits to allow control of free-standing lamps from

3567-447: A mechanism that springs it into another position when released by an operator. The momentary push-button 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

3690-495: A portion of a house is rewired. It is not unusual to see century-old light switches still in functional use. Manufacturers introduce various new forms and styles, but for the most part decoration and fashion concerns are limited to the face-plates or wall-plates. Even the "modern" dimmer switch with knob is at least forty years old, and in even the newest construction the familiar toggle and rocker switch formats predominate. The direction which represents "on" also varies by country. In

3813-513: 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,

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3936-535: 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

4059-560: A solid (e.g. plastic) coating may be impractical. Wires that touch each other produce cross connections, short circuits , and fire hazards. In coaxial cable the center conductor must be supported precisely in the middle of the hollow shield to prevent electro-magnetic wave reflections. Wires that expose high voltages can cause human shock and electrocution hazards. Most insulated wire and cable products have maximum ratings for voltage and conductor temperature. The product may not have an ampacity (current-carrying capacity) rating, since this

4182-437: 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

4305-545: A sufficient amount of wetting current is a crucial step in designing 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. 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). A switch normally maintains its set position once operated. A biased switch contains

4428-935: A sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as electrical breakdown , and the voltage at which it occurs is called the breakdown voltage of an insulator. Some materials such as glass , paper and PTFE , which have high resistivity , are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables . Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature. Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment

4551-403: 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,

4674-400: Is a common problem with mechanical switches, relays and battery contacts , which arises as the result of electrical contact resistance (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

4797-483: Is a criterion. Porcelain has a dielectric strength of about 4–10 kV/mm. Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains. Some insulator manufacturers stopped making glass insulators in the late 1960s, switching to ceramic materials. Some electric utilities use polymer composite materials for some types of insulators. These are typically composed of

4920-436: Is a manually operated electromechanical device with one or more sets of electrical contacts , 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)

5043-626: Is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials— semiconductors and conductors —conduct electric current more easily. The property that distinguishes an insulator is its resistivity ; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals . A perfect insulator does not exist because even insulators contain small numbers of mobile charges ( charge carriers ) which can carry current. In addition, all insulators become electrically conductive when

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5166-486: 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 circuits that respond fast enough to misinterpret the on‑off pulses as a data stream. In the design of micro-contacts, controlling surface structure ( surface roughness ) and minimizing the formation of passivated layers on metallic surfaces are instrumental in inhibiting chatter. In

5289-803: Is air. A variety of solid, liquid, and gaseous insulators are also used in electrical apparatus. In smaller transformers , generators , and electric motors , insulation on the wire coils consists of up to four thin layers of polymer varnish film. Film-insulated magnet wire permits a manufacturer to obtain the maximum number of turns within the available space. Windings that use thicker conductors are often wrapped with supplemental fiberglass insulating tape . Windings may also be impregnated with insulating varnishes to prevent electrical corona and reduce magnetically induced wire vibration. Large power transformer windings are still mostly insulated with paper , wood, varnish, and mineral oil ; although these materials have been used for more than 100 years, they still provide

5412-418: 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 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

5535-401: Is between 0.5 A, mainly limited to low powered lamps at mains voltage, up to 6 or even 10 A (like heaters) . Higher current ratings may also allow usage in high current but low voltage (6-24 V) applications. A dimmer switch , properly called a dimmer control , contains a solid-state circuit to allow changing the brightness by reducing the average voltage applied to the lamp. In principle, it

5658-628: Is called insulation . The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers . They support the weight of the suspended wires without allowing the current to flow through the tower to ground. Electrical insulation is the absence of electrical conduction . Electronic band theory (a branch of physics) explains that electric charge flows when quantum states of matter are available into which electrons can be excited. This allows electrons to gain energy and thereby move through

5781-545: Is constructed of a ceramic or glass disc with a metal cap and pin cemented to opposite sides. To make defective units obvious, glass units are designed so that an overvoltage causes a puncture arc through the glass instead of a flashover. The glass is heat-treated so it shatters, making the damaged unit visible. However the mechanical strength of the unit is unchanged, so the insulator string stays together. Standard suspension disc insulator units are 25 centimetres (9.8 in) in diameter and 15 cm (6 in) long, can support

5904-471: Is dependent on the surrounding environment (e.g. ambient temperature). In electronic systems, printed circuit boards are made from epoxy plastic and fibreglass. The nonconductive boards support layers of copper foil conductors. In electronic devices, the tiny and delicate active components are embedded within nonconductive epoxy or phenolic plastics, or within baked glass or ceramic coatings. In microelectronic components such as transistors and ICs ,

6027-406: Is easy to design silent switches in which the mechanical contacts do not directly control the current, but simply signal a solid-state device such as a thyristor to complete the circuit. Many variations on this theme have been created and marketed. " Touch-plate " devices can be operated by touching or merely waving a hand near the switch. Touch switches have no moving parts and electronically switch

6150-400: Is exceeded, electrical breakdown occurs, and the material ceases being an insulator, passing charge. This is usually accompanied by physical or chemical changes that permanently degrade the material and its insulating properties. When the electric field applied across an insulating substance exceeds in any location the threshold breakdown field for that substance, the insulator suddenly becomes

6273-434: Is near-universal, and toggle style switches would be considered old-fashioned. In Australia and New Zealand, a small rocker switch is almost universally used, in the form of a 16 mm (0.63 in) switch mechanism, which is mounted from behind into a wall-plate—attaching via mounting lugs, as shown in the photo on the left. A slightly larger "cover plate", supplied with the wall-plate, or additional to it, then clips over

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6396-468: Is somewhat similar in appearance to these modules, but the design of the keystone mountings are different, and keystone modules can be removed without a tool. (A similar system, but with bigger switches, is used in Italy.) As shown in the disassembly photo, the switch actuator pivots in two holes in the sides of the plastic switch body. An actuator bar slides in two grooves inside the actuator, pressed down by

6519-409: Is that insulator strings with different breakdown voltages , for use with different line voltages, can be constructed by using different numbers of the basic units. String insulators can be made for any practical transmission voltage by adding insulator elements to the string. Also, if one of the insulator units in the string breaks, it can be replaced without discarding the entire string. Each unit

6642-468: 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

6765-513: 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. 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 ),

6888-423: 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 . Automatically operated switches can be used to control

7011-484: The Hammond organ , 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 organs have a switchable replica of this sound effect. The effects of contact bounce can be eliminated by: All of these methods are referred to as 'debouncing'. When

7134-436: The contact resistance , and wetting current of a mechanical switch. Sometimes the contacts are plated with noble metals , 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

7257-420: The electronics 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 wiring (i.e., house and building wiring by electricians ), names generally involve the suffix "-way" ; however, these terms differ between British English and American English (i.e.,

7380-405: 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 switches consist of

7503-461: The CFL or LED until the voltage across it rises to the point where it produces a brief discharge through the CFL. This cycle may repeat indefinitely, resulting in repetitive brief flashing of the lamp(s) (and the light inside the switch) while the illuminated switch is in the "off" position. An alternative design to the toggle switch is the rocker switch. Large switches of this design are commonly known in

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7626-457: The US, Canada, European countries, Russia, etc., it is usual for the "on" position of a toggle switch to be "up", whereas in many other countries such as the UK, India, Australia, New Zealand (Commonwealth countries), Ireland and China, it is "down". (In multiway switching , the correspondence between a single switch's state and whether lights are on or off depends on the state of the other switch[es] in

7749-538: The United States as "decorator" or "Decora" style. "Decora" is a trademark of Leviton , and the term in recent years has become a genericized trademark in the United States for any rocker light switch regardless of brand. Switches of this design sit almost flush with the wall plate, and are activated by "rocking" a flat, broad lever, rather than pushing a short protruding actuator up or down. In Europe, Brazil, Hong Kong, Malaysia, Singapore, and India this type

7872-495: The United States in the 1960s. Although the switches had adequate ratings for usage on 120 V circuits and had advantages of compactness and distinctive appearance, they failed to establish themselves in the American market. Where lighting circuits must not be accidentally switched off, for example, corridor and restroom lighting controls in public buildings such as schools, a tamper-resistant switch may be installed. These require

7995-499: The aesthetic quality of many insulator designs and finishes. One collectors organisation is the US National Insulator Association, which has over 9,000 members. Often a broadcasting radio antenna is built as a mast radiator , which means that the entire mast structure is energised with high voltage and must be insulated from the ground. Steatite mountings are used. They have to withstand not only

8118-978: The air and must be carried out cautiously. Wire insulated with felted asbestos was used in high-temperature and rugged applications from the 1920s. Wire of this type was sold by General Electric under the trade name "Deltabeston." Live-front switchboards up to the early part of the 20th century were made of slate or marble. Some high voltage equipment is designed to operate within a high pressure insulating gas such as sulfur hexafluoride . Insulation materials that perform well at power and low frequencies may be unsatisfactory at radio frequency , due to heating from excessive dielectric dissipation. Electrical wires may be insulated with polyethylene , crosslinked polyethylene (either through electron beam processing or chemical crosslinking), PVC , Kapton , rubber-like polymers, oil impregnated paper, Teflon , silicone, or modified ethylene tetrafluoroethylene ( ETFE ). Larger power cables may use compressed inorganic powder , depending on

8241-436: The antenna from short circuiting to ground or creating a shock hazard. Often guy cables have several insulators, placed to break up the cable into lengths that prevent unwanted electrical resonances in the guy. These insulators are usually ceramic and cylindrical or egg-shaped (see picture). This construction has the advantage that the ceramic is under compression rather than tension, so it can withstand greater load, and that if

8364-754: The application. Flexible insulating materials such as PVC (polyvinyl chloride) are used to insulate the circuit and prevent human contact with a 'live' wire – one having voltage of 600 volts or less. Alternative materials are likely to become increasingly used due to EU safety and environmental legislation making PVC less economic. In electrical apparatus such as motors, generators, and transformers, various insulation systems are used, classified by their maximum recommended working temperature to achieve acceptable operating life. Materials range from upgraded types of paper to inorganic compounds. All portable or hand-held electrical devices are insulated to protect their user from harmful shock. Class I insulation requires that

8487-551: The arc. 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

8610-461: The arc. For example, the switch contacts may operate in a vacuum, immersed in mineral oil , or in 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. When a switch is designed to switch significant power,

8733-610: The assembly, as an additional insulating barrier covering the deep set wall-plate mounting screws - which are "deep set" to prevent inadvertent human contact. The "cover plate" can be removed without the use of tools, such as when wall painting is required. While larger "decorator" style switches are readily available in Australia, the advantage of the smaller mechanisms is that wall-plates are available to mount from one to six individual switch mechanisms, or other correspondingly sized "mechanisms" - such as dimmers and indicator lights - in

8856-424: The billions, as well as in many other forms of electric switch. The toggle light switch was invented in 1916 by William J. Newton. As a component of an electrical wiring or home wiring system, the installation of light switches is regulated by some authority concerned with safety and standards. In different countries the standard dimensions of the wall mounting hardware (boxes, plates, etc.) may differ. Since

8979-436: The circuit.) The switches may be single or multiple, designed for indoor or outdoor use. Optional extras may include dimmer-controls, environmental protection, weather and security protection. In residential and light commercial lighting systems, the light switch directly controls the circuit feeding the lamps. In larger lighting systems, for example warehouses or outdoor lighting systems, the required current may be too high for

9102-414: The common contact bar is forced in the opposite direction by the compression spring, acting via the actuator bar, thus breaking the connection with the existing contact and making connection with the other contact. The common contact bar is made of copper, with an inlay of harder contact metal on the underside. While it is free to move the required distance lengthwise, it is constrained from moving sideways by

9225-422: The conductor inside them. Insulators used for high-voltage power transmission are made from glass , porcelain or composite polymer materials . Porcelain insulators are made from clay , sapphire (A Diamond Cubic Carbon), boron nitride , quartz or alumina and feldspar , and are covered with a smooth glaze to shed water. Insulators made from porcelain rich in alumina are used where high mechanical strength

9348-427: The construction of the molded plastic body. The screw terminals are hollow and allow up to at least three 1 mm (CSA) wires, twisted together, to be inserted to a depth of up to 10 millimetres (0.39 in) and secured with a set screw . The contact terminal set screws are installed at a slight angle to allow easier screwdriver access after the switch mechanism has been installed into a wall-plate - before fixing

9471-480: The contacts and pops out the previously depressed button so the process can be reversed. In the U.S., the buttons were commonly black; the "on" button typically had a white mother-of-pearl (real or simulated) inlay to indicate its function. By convention, the switch was customarily installed with the "on" button on top. Push-button switch reproductions are available on the market today for vintage or authentic styling. The toggle mechanism provides "snap-action" through

9594-409: The contacts would separate or come together very quickly, however much or little pressure was exerted by the user on the switch actuator. The action of this "quick break" mechanism meant that there was insufficient time for an arc to form, and the switch would thus have a long working life. This "quick break" technology is still in use in almost every ordinary light switch in the world today, numbering in

9717-407: The current decreases to a steady-state value. A switch designed for an incandescent lamp load can withstand this inrush 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

9840-508: The devices have both basic and supplementary insulation, each of which is sufficient to prevent electric shock . All internal electrically energized components are totally enclosed within an insulated body that prevents any contact with "live" parts. In the EU , double insulated appliances all are marked with a symbol of two squares, one inside the other. Conductors for overhead high-voltage electric power transmission are bare, and are insulated by

9963-587: The disc at the high voltage end, to reduce the electric field across that disc and improve flashover voltage. In very high voltage lines the insulator may be surrounded by corona rings . These typically consist of toruses of aluminium (most commonly) or copper tubing attached to the line. They are designed to reduce the electric field at the point where the insulator is attached to the line, to prevent corona discharge , which results in power losses. The first electrical systems to make use of insulators were telegraph lines ; direct attachment of wires to wooden poles

10086-444: The face-plates used must cover this hardware, these standards determine the minimum sizes of all wall mounted equipment. Hence, the shape and size of the boxes and face-plates, as well as what is integrated, varies from country to country. The dimensions, mechanical designs, and even the general appearance of light switches have changed slowly over time. Switches typically remain in service for many decades, often being changed only when

10209-644: The first to produce ceramic insulators were companies in the United Kingdom, with Stiff and Doulton using stoneware from the mid-1840s, Joseph Bourne (later renamed Denby ) producing them from around 1860 and Bullers from 1868. Utility patent number 48,906 was granted to Louis A. Cauvet on 25 July 1865 for a process to produce insulators with a threaded pinhole: pin-type insulators still have threaded pinholes. The invention of suspension-type insulators made high-voltage power transmission possible. As transmission line voltages reached and passed 60,000 volts,

10332-407: 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

10455-431: The insulator breaks, the cable ends are still linked. These insulators also have to be equipped with overvoltage protection equipment. For the dimensions of the guy insulation, static charges on guys have to be considered. For high masts, these can be much higher than the voltage caused by the transmitter, requiring guys divided by insulators in multiple sections on the highest masts. In this case, guys which are grounded at

10578-439: The insulators required become very large and heavy, with insulators made for a safety margin of 88,000 volts being about the practical limit for manufacturing and installation. Suspension insulators, on the other hand, can be connected into strings as long as required for the line's voltage. A large variety of telephone, telegraph and power insulators have been made; some people collect them, both for their historic interest and for

10701-638: The length of the leakage path along the surface from one end to the other, called the creepage length, to minimise these leakage currents. To accomplish this the surface is moulded into a series of corrugations or concentric disc shapes. These usually include one or more sheds ; downward facing cup-shaped surfaces that act as umbrellas to ensure that the part of the surface leakage path under the 'cup' stays dry in wet weather. Minimum creepage distances are 20–25 mm/kV, but must be increased in high pollution or airborne sea-salt areas. Insulators are characterized in several common classes: An insulator that protects

10824-649: The light circuit. As of 1986 these remain specialty items. Electronic switches provide flexibility in terms of different interfaces for their operations, such as touch plates, soft-touch controls, pressure or light sensor based control, interactive touch-screens (which are widely used in aircraft for lighting control), and others. Public buildings such as hospitals frequently save energy by using motion detector switches, also known as occupancy sensors . The occupancy sensors can also be used in residential applications such as in bathrooms, garages, and hallways. A wireless light switch provides remote control of lighting using

10947-595: The mercury to connect either side of the wheel in only one position. Some of these switches were also equipped with a neon lamp connected across the contacts, and thus in series with the electrical load. This caused the indicator to glow faintly when the switch was off, as an aid to finding the switch in a dark room. By the 1970s, other quiet switch designs that did not require mercury (and were thus simpler and cheaper to produce) came into widespread use, gradually replacing both conventional "snap" toggle switches and mercury-based quiet switches. A light switch combined with

11070-477: The metal body and other exposed metal parts of the device be connected to earth via a grounding wire that is earthed at the main service panel—but only needs basic insulation on the conductors. This equipment needs an extra pin on the power plug for the grounding connection. Class II insulation means that the device is double insulated . This is used on some appliances such as electric shavers, hair dryers and portable power tools. Double insulation requires that

11193-488: The middle of the plug and consumer or they may be mounted at the end of the cable. There are also more sophisticated cord mounted switches, like multiple switching (for lamps with more than one bulb, or fans with more speeds, in this case they have one input and 2 or more outputs), variators and dimmers (light dimmers, electric pillows and matresses or some fans with more speeds). Some older heaters may also use such switches, but with higher ratings. Usually their current rating

11316-438: 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 sensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control

11439-412: The opening contacts. Switches for 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. When turned on, an incandescent lamp draws a large inrush current of about ten times the steady-state current; as the filament heats up, its resistance rises and

11562-448: 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. A rotary switch operates with a twisting motion of the operating handle with at least two positions. One or more positions of

11685-424: 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

11808-503: The power cord, usually stays on the floor and it is operated by foot. It is also used for other small home appliances, like fans or heaters (usually higher ratings). This type of switch is mounted on the power cord, both in middle or at the end. They are light weight, and they are used mainly for low power devices, like table lamps, table fans, radios and many other low power devices. Usually they are single pole single throw, but can also double pole single throw. They can be mounted either in

11931-482: The result of roughness and oxide films, they exhibit contact resistance , 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. In

12054-403: The room's light switches. In North American site-built and mobile homes , often living rooms and bedrooms have a switched receptacle for a floor or table lamp. Such receptacles are referred to as switched outlets or half-hot outlets . The push-button light switch has two buttons: one that closes the contacts and one that opens the contacts. Pushing the raised button opens or closes

12177-622: The same design is also used on Australian power outlet wall-plates. It is now extremely rare to find any other type of switch in Australian homes, although the Australian Wiring Standard AS 3112 does not forbid other types. While many variations of Australian designs and cover plates are available, some designers and renovators may import UK- and European-designed switches when they desire a particular finish. However, while standard Australian wall mounting plates have

12300-463: The same dimensions as those used in North America, they have different dimensions from those used in the UK or Europe. Switches (and other mechanisms) of this Australian design series are currently available in the UK (and other countries), together with wall-plates appropriate to the mounting standards of the countries concerned. For a short time, Australian rocker switches were exported to

12423-669: The same space as one (or two) switches of larger design could be mounted. Since the mechanisms are small, they can also be mounted into " architrave " plates, for mounting in positions where it is not possible to mount a "standard" sized wall-plate. An example is shown in the picture below on the right. All of the switch mechanisms have no exposed metal parts requiring grounding (earthing). While switches, wall-plates, and cover plates from different manufacturers tend not to be interchangeable, switch mechanisms of this type have been available in Australia since 1951. The keystone module system for extra-low voltage electrical jacks (patented in 1975)

12546-581: 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

12669-705: The silicon material is normally a conductor because of doping, but it can easily be selectively transformed into a good insulator by the application of heat and oxygen. Oxidised silicon is quartz , i.e. silicon dioxide , the primary component of glass. In high voltage systems containing transformers and capacitors , liquid insulator oil is the typical method used for preventing arcs. The oil replaces air in spaces that must support significant voltage without electrical breakdown . Other high voltage system insulation materials include ceramic or glass wire holders, gas, vacuum, and simply placing wires far enough apart to use air as insulation. The most important insulation material

12792-636: The simplest case, a switch has two conductive pieces, often metal , 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 , 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

12915-449: The simultaneous actuation of multiple sets of electrical contacts , or the control of large amounts of electric current or 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

13038-409: The small current required for the switch's illuminating source is too small to produce any visible light from such devices controlled by the illuminated switch. However, if they control only compact fluorescent lamps (CFLs) and/or LED lamps , the small amount of current required to energize the lighting source within switch also slowly charges the internal input capacitor in the electronic ballast of

13161-437: 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

13284-416: The spring-loaded toggle switches that were then the norm. One form of mercury light switch uses a sealed glass vial that is tipped by the toggle lever, causing a drop of liquid metallic mercury to roll from one end to the other, bridging a pair of contacts to complete the circuit. Another style of mercury light switch uses a metal wheel with an insulator separating the two halves that has a hole which allows

13407-412: The spring. When the mechanism passes over the center point, the spring energy is released and the spring, rather than the actuator, drives the contacts rapidly and forcibly to the closed position with an audible "snapping" sound. This mechanism is safe, reliable, and durable, but produces a loud snap or click. Illuminated switches incorporate a small neon lamp or LED , allowing the user easily to locate

13530-455: The surrounding air. Conductors for lower voltages in distribution may have some insulation but are often bare as well. Insulating supports are required at the points where they are supported by utility poles or transmission towers . Insulators are also required where wire enters buildings or electrical devices, such as transformers or circuit breakers , for insulation from the case. Often these are bushings , which are hollow insulators with

13653-413: 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

13776-404: The switch in the dark. Household illuminated switches were introduced in the mid-1950s. Single-pole illuminated switches derive the power to energize their in-built illuminating source (usually, a "neon" lamp) from the current passing through the lamp(s) which they control. Such switches work satisfactorily with incandescent lamps, halogen lighting, and non-electronic fluorescent fixtures, because

13899-415: 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

14022-450: The terms two way and three way are used with different meanings). Form A 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 (also called chatter )

14145-431: The thermal energy of the valence electrons is sufficient to put them in the conduction band. In certain capacitors, shorts between electrodes formed due to dielectric breakdown can disappear when the applied electric field is reduced. A flexible coating of an insulator is often applied to electric wire and cable; this assembly is called insulated wire . Wires sometimes don't use an insulating coating, just air, when

14268-420: 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

14391-407: 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

14514-430: The use of an "over-center" geometry. The design was patented in 1916 by William J. Newton and Morris Goldberg. The switch actuator does not control the contacts directly, but through an intermediate arrangement of springs and levers. Turning the actuator does not initially cause any motion of the contacts, which in fact continue to be positively held open by the force of the spring. Turning the actuator gradually stretches

14637-400: The voltage of the mast radiator to ground, which can reach values up to 400 kV at some antennas, but also the weight of the mast construction and dynamic forces. Arcing horns and lightning arresters are necessary because lightning strikes to the mast are common. Guy wires supporting antenna masts usually have strain insulators inserted in the cable run, to keep the high voltages on

14760-466: 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 mechanism to assure quick motion of switch contacts, regardless of

14883-450: The wall-plate to the wall. Also shown is a "loop" connection terminal. This terminal plays no part in the action of the switch but, because there is available space, it is provided as an insulated terminal for joining other wires, if required (such as the neutral wires). Each Australian rocker switch mechanism is actually a single-pole, double-throw (SPDT) Switch, also known as a "two-way switch", and has three terminals. A switch of basically

15006-521: Was found to give very poor results, especially during damp weather. The first glass insulators used in large quantities had an unthreaded pinhole. These pieces of glass were positioned on a tapered wooden pin, vertically extending upwards from the pole's crossarm (commonly only two insulators to a pole and maybe one on top of the pole itself). Natural contraction and expansion of the wires tied to these "threadless insulators" resulted in insulators unseating from their pins, requiring manual reseating. Amongst

15129-460: Was invented by John Henry Holmes in 1884 in the Shieldfield district of Newcastle upon Tyne. The "quick-break" switch overcame the problem of a switch's contacts developing electric arcing whenever the circuit was opened or closed. Arcing would cause pitting on one contact and the build-up of residue on the other, and the switch's useful life would be diminished. Holmes' invention ensured that

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