AC power plugs and sockets: Wikis

  
  

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AC power plugs and sockets are devices for removably connecting electrically-operated devices to the commercial power supply.

An electric plug is a male electrical connector with contact prongs to connect mechanically and electrically to slots in the matching female socket.

Wall sockets (sometimes also known as power points,[1][2] power sockets, electric receptacles, or electrical outlets) are female electrical connectors that have slots or holes which accept and deliver current to the prongs of inserted plugs. To reduce the risk of injury or death by electric shock, some plug and socket systems incorporate various safety features. Sockets are designed to accept only matching plugs and reject all others.

Contents

Terminology

There are substantial differences between American and British nomenclature related to power plugs and sockets.

British English American English Meaning
mains power line power The primary electrical power supply wires entering a building, connected to the Main fuses or circuit breakers.
domestic power Single-phase 230 V power as used in a single-family residence
earth connection ground or grounding connection Safety connection to the earth or ground
live connection hot or live connection Phase ("active") connection
neutral connection cold or neutral connection return connection
flex/mains lead, mains wire/wiring line cord/power cord Flexible electric cable from plug to appliance
4/6/8 way mains extension lead/adaptor power bar Device providing multiple outlets from a single outlet, usually on a flex lead
pin, (plug) pin, prong, blade (plug) Male part of an electrical connector
socket socket, outlet, receptacle Female part of an electrical connector

In the United States, the live contact may be called live, hot or ungrounded. The neutral contact may be called cold, neutral, return, the grounded conductor, or (in the National Electrical Code), the identified conductor. The earth contact is called ground or the grounding conductor.

In the United Kingdom the word line is occasionally used to denote the live terminal or wire. In electrical engineering, the line voltage is that between the live conductors of the three-phase distribution system, while the phase voltage is that between live and neutral.

Live conductors are called phases when there is more than a single phase in use. Pins are also known as prongs, contacts, blades, or terminals.

In Australia, the live contact is called active.

The three contacts

Each receptacle has two or three wired contacts. The contacts may be steel or brass, and may be plated with zinc, tin, or nickel. The live contact carries current from the source to the load. The neutral returns current to the source. Many receptacles and plugs also include a third contact for a connection to earth ground, intended to protect against insulation failure of the connected device.

Polarisation

Polarised plugs and sockets are those designed to connect only in one orientation, so the live and neutral conductors of the outlet are connected (respectively) to the live and neutral poles of the appliance. Polarisation is maintained by the shape, size, or position of plug pins and socket holes to ensure that a plug fits only one way into a socket. This is so switches interrupt the live wire. If the neutral wire were interrupted instead, the device would be deactivated but its internal wiring would still be live. This is a shock hazard; if the energised parts are touched, current travels to earth through the body. Devices that especially present this hazard include toasters and other appliances with exposed heating elements, which with reversed polarity can remain live even when they are cool to the touch, and screw-in light bulbs, which with reversed polarity, exposed portions of the socket shell remain energised even though the lamp is switched off.

Interchange of the live and neutral wires in the wiring behind the walls or in the hookup of sockets defeats the safety purpose of polarised sockets and plugs; a circuit tester can be used to detect swapped wires.

Unpolarised plugs and sockets are those which can connect either way around, so live and neutral wires are connected at random. Unpolarised plug/socket systems such as the Europlug rely on device construction requirements to avoid the shock hazards created by interchange of live and neutral connections; for example, double insulation, a particular IP protection rating, or double switching.

(Further information on the configuration of specific types of polarised and unpolarised plugs is below in the section "Types in present use".)

History

Early history

When electricity was first introduced into the household, it was primarily used for lighting. At that time, many electricity companies operated a split-tariff system where the cost of electricity for lighting was lower than that for other purposes. This led to portable appliances (such as vacuum cleaners, electric fans, and hair driers) being connected to the light fitting.

U.S. Patent 774,250. The first electric power plug and receptacle.

However, as electricity became a common method of lighting houses and operating labour-saving appliances, a safe means of connection to the electric system other than using a light socket was needed. The original two pin electrical plug and socket were invented by Harvey Hubbell and patented in 1904. Other manufacturers adopted the Hubbell pattern and by 1915 they were widespread, although in the 1920s and even later, household and light commercial equipment was still powered through cables connected with Edison screw-base adapters to lampholders.[3][4][5]

The grounded consumer plug was invented by Albert Büttner, who patented the Schuko-system in 1926[6]. The American version of the grounded plug, the three-prong plug was invented by Philip F. Labre, while he was attending the Milwaukee School of Engineering (MSOE). It is said that his landlady had a cat which would knock over her fan when it came in the window. When she plugged the fan back in, she would get an electric shock. Labre figured out that if the plug were grounded, the electricity would go to earth through the plug rather than through his landlady. He applied a patent on May 12, 1927[7] and was issued a US patent for grounding receptacle and plug in June, 1928.[8] As the need for safer installations became apparent, earthed three-contact systems were made mandatory in most industrial countries.

Proliferation of standards

During the first fifty years of commercial use of electric power, standards developed rapidly based on growing experience. Technical, safety, and economic factors influenced the development of all wiring devices and numerous varieties were invented. Gradually the desire for trade eliminated some standards that had been used only in a few countries. Former colonies may retain the standards of the colonising country, occasionally—as with the UK and a number of its former colonies—after the colonising country has changed its standard. Sometimes offshore industrial plants or overseas military bases use the wiring practices of their controlling country instead of the surrounding region. Hotels and airports may maintain receptacles of foreign standards for the convenience of travellers. Some countries have multiple voltages, frequencies and plug designs in use, which can create inconvenience and safety hazards.

Design for safety

Design features and aspects of plugs and sockets have evolved to reduce the risk of electric shock and equipment damage. Depending on the plug/socket system, safety measures may include pin and slot configuration to permit only the correct insertion of plug into socket, earth pins longer than power pins so the device becomes earthed before power is connected, insulated pin shanks to reduce or eliminate live-contact exposure when a plug is partially inserted in a socket, socket slot shutters that open only for the correct plug, as well as inbuilt fuses and switches.

Consolidation of standards

In recent years many countries have settled on one of a few de facto standards, which became formalised as official national standards, although there remain older installations of obsolete wiring in most countries. Some buildings have wiring that has been in use for almost a century and which pre-dates all modern standards.

There has been some movement towards consolidation of standards for international interoperability. For example, the CEE 7/7 plug (see below) has been adopted in several European countries and is compatible with both Type E and Type F sockets, while the unpolarised Europlug is compatible with an even greater proportion of European and other socket types. IEC 60906-1 has been proposed as a common standard for all 230-V plugs and sockets worldwide but has only been adopted in Brazil to date.

IEC power cord with CEE 7/7 plug at left end.

Many manufacturers of electrical devices like personal computers have adopted the practice of putting a single world-standard IEC connector on the device, and supplying for each country a power cord equipped with a standard IEC connector on one end and a national power plug at the other. The device itself is designed to adapt to a wide range of voltage and frequency standards. This has the practical benefit of reducing the amount of testing required for approval, and reduces the number of different product variations that must be produced to serve world markets.

World maps

Voltage/Frequency.
Plugs.

There are two basic standards for voltage and frequency in the world. One is the North American standard of 110–120 volts at a frequency of 60 Hz, which uses plugs A and B, and the other is the European standard of 220–240 volts at 50 Hz, which uses plugs C to M. The differences arose for historical reasons as discussed in the article Mains electricity.

Countries on other continents have adopted one of these two voltage standards, although some countries use variations or a mixture of standards. The outline maps show the different plug types, voltages and frequencies used around the world,[9] color-coded for easy reference.

Types in present use

Electrical plugs and their sockets differ by country in shape, size and type of connectors. The type used in each country is set by national standards legislation.[10] In this article each type is designated by a letter designation from a U.S. government publication [9], plus a short comment in parentheses giving its country of origin and number of contacts. Subsections then detail the subtypes of each type as used in different parts of the world.

IEC Classes are assigned to electrical devices depending on whether or not they are earthed and the degree of insulation they incorporate. Class I, for example, refers to earthed equipment, while class II refers to unearthed equipment protected by double insulation.

Special purpose sockets may be found in residential, industrial, commercial or institutional buildings. These may be merely labelled or coloured, or may have different arrangements of pins or keying provisions. Some special-purpose systems are incompatible with general-purpose lighting and appliances. Examples of systems using special purpose sockets include:

  • "clean" ground for use with computer systems,
  • emergency power supply,
  • uninterruptible power supply, for critical or life-support equipment,
  • isolated power for medical instruments,
  • "balanced" or "technical" power used in audio and video production studios,
  • theatrical lighting
  • outlets for electric clothes dryers, electric ovens, and air conditioners with higher current rating.

Depending on the nature of the system, special-purpose sockets may just identify a reserved use of a system (for example, computer power) or may be physically incompatible with utility sockets to prevent use of unintended equipment which could create electrical noise or other problems for the intended equipment on the line.

Type A

Unpolarized type A plug
NEMA 1–15 (North American 15 A/125 V ungrounded)
Unusual American 5-receptacle Type A outlet, ca. 1928

This plug and socket, with two flat parallel non-coplanar blades and slots, is used in most of North America and on the east coast of South America on devices not requiring a ground connection, such as lamps and "double-insulated" small appliances. It has been adopted by 38 countries outside North America, and is standardized in the U.S. by the National Electrical Manufacturers Association.[11] NEMA 1–15 sockets have been prohibited in new construction in the United States and Canada since 1962, but remain in many older homes and are still sold for replacement. Type A plugs are still very common because they are compatible with type B (three-prong) sockets.

Initially, the plug's prongs and the socket's slots were the same height, so the plug could be inserted into the socket either way around. Most sockets and plugs manufactured from the 1950s onward are polarized by means of a neutral blade/slot wider than the live blade/slot, so the plug can be inserted only the right way. Polarized type A plugs will not fit in unpolarized type A sockets, because both slots are narrow, but both unpolarized and polarized type A plugs will fit in polarized type A sockets and in type B (three-prong) sockets. Some devices that do not distinguish between neutral and live, such as sealed electronic power supplies, are still produced with unpolarized type A pins (both narrow).

Japanese outlet with earthing post, for a washing machine.
JIS C 8303, Class II (Japanese 15 A/100 V ungrounded)

The Japanese plug and socket are identical to NEMA 1–15. However, the Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by MITI or JIS.[12]

Many Japanese outlets and multi-plug adapters are unpolarized—the slots in the sockets are the same size—and will accept only unpolarized plugs. Japanese plugs generally fit into most North American outlets without trouble, but polarized North American plugs may require adapters or replacement non-polarized plugs to connect to older Japanese outlets. However, in Japan voltage is supplied at only 100 volts and the frequency in eastern Japan is 50 rather than 60 Hz, so North American devices which can be plugged into Japanese sockets may not function properly though devices with rectified power supplies may work without problems.

Type B

NEMA 5–15 plug, left. Decorative-style duplex outlet, center. Ordinary duplex outlet, right.
NEMA 5–15 (North American 15 A/125 V grounded)

The type B plug has two flat parallel blades like type A, but has a round or U-shaped grounding prong (American standard NEMA 5-15/CSA 22.2, No.42).[11] It is rated for 15 amperes at 125 volts. The ground pin is longer than the live and neutral blades, so the device is grounded before the power is connected. Nearly always both current blades on type B plugs are narrow since the ground pin enforces polarity. This has the unfortunate effect that when a misguided individual cuts off the ground pin to fit it to a type A outlet or extension cord, the live/neutral polarity is lost. Type A plugs are also compatible with type B sockets. In this case, the socket retains polarity enforcement. Adapters that allow a type B plug to be fitted to a type A outlet are readily available. Proper grounding is dependent on the outlet being an ordinary duplex receptacle with a grounded center screw, and the grounding tab of the adapter being connected to that screw.

The 5–15 socket is standard in all of North America (Canada, the United States and Mexico). It is also used in Central America, the Caribbean, northern South America (Colombia, Ecuador, Venezuela and part of Brazil), Japan, Taiwan and Saudi Arabia. Looking directly at a type B outlet with the ground at the bottom, the neutral slot is on the left, and the live slot is on the right. They may also be installed with the ground at the top or on either side.

In some parts of the United States and all of Canada, tamper-resistant outlets are now required in new construction. These prevent contact by objects like keys or paper clips inserted into the receptacle.[13]

5–20RA T-slot receptacle mounted with the ground hole up. The neutral connection is the wider T-shaped slot on the lower right.

In the theater, this connector is sometimes known as PBG for "Parallel Blade with Ground", Edison or Hubbell, the name of a common manufacturer.[citation needed]

NEMA 5–20 (North American 20 A/125 V grounded)

This is a 20-amp receptacle; type 5-20A has a T-slot for the neutral blade which allows either 15-ampere parallel-blade plugs or 20-ampere plugs to be used.

JIS C 8303, Class I (Japanese 15 A/100 V grounded)

Japan also uses a Type B plug similar to the North American one.[12] However it is less common than its Type A equivalent.

Type C

CEE 7/16 plug and socket

(Not to be confused with the 3-blade C13 and C14 IEC connectors)

CEE 7/16 (Europlug 2.5 A/250 V ungrounded)

This two-prong plug is popularly known as the Europlug. The plug is ungrounded and has two round 4 mm (0.157 in) pins, which usually converge slightly towards their free ends. It is described in CEE 7/16[14] and is also defined in Italian standard CEI 23-5 and Russian standard GOST 7396. This plug is intended for use with devices that require 2.5 amps or less. Because it is unpolarised, it can be inserted in either direction into the socket, so live and neutral are connected at random. The separation and length of the pins allow its safe insertion in most CEE 7/17, Type E (French), type F (CEE 7/4 "Schuko"), Type H (Israeli), CEE 7/7, Type J (Swiss), Type K (Danish) and Type L (Italian) outlets, as well as BS 4573 UK shaver sockets. It can be forced into type D (5 amp) and G sockets, it is a common misconception that this is unsafe; however, there is, technically, no reason why it would create any more of a hazard than if it were plugged into a normal Type C socket. The caveat is that plugs going into type G should be fused appropriately as a faulty device can pull up to 32 A from the ring circuit.

The Europlug (plug only, not socket from the picture) is used in Class II applications throughout continental Europe (Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Czech Republic, Croatia, Denmark, Estonia, Finland, France, Germany, Greece, Greenland, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Macedonia, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and Ukraine). It is also used in the Middle East, most African nations, South America (Brazil, Chile, Argentina, Uruguay, Peru and Bolivia), Asia (Bangladesh, Indonesia and Pakistan) as well as Russia and the former Soviet republics, such as Armenia, Georgia, and many developing nations. It is also used alongside the BS 1363 in many nations, particularly former British colonies.

CEE 7/17 plug
CEE 7/17 (German/French 16 A/250 V ungrounded)

This plug also has two round pins but the pins are 4.8 mm (0.189 in) in diameter like types E and F and the plug has a round plastic or rubber base that stops it being inserted into small sockets intended for the Europlug. Instead, it fits only into large round sockets intended for types E and F. The base has holes in it to accommodate both side contacts and socket earth pins. It is used for large appliances, and in South Korea for all domestic non-earthed appliances. It is also defined in Italian standard CEI 23-5. Can also be safely inserted in to Israeli type H sockets, although with some difficulty.


BS 4573 socket
BS 4573 (UK shaver)

In the United Kingdom and Ireland, what appears to be a larger version of the type C plug exists for use with shavers (electric razors) in bath or shower rooms.[15] In fact it was not derived from the type C plug at all, but was a legacy from the obsolete 2 pin 5 amp plug used in Britain in the 1920s and 1930s but still prevalent, especially in bathrooms, as late as the 1960s. It has 0.2 in (5.08 mm) diameter pins 58 in (15.88 mm) apart, and the sockets for this plug are often designed to accept unearthed CEE 7/16, US or Australian plugs as well. Sockets are often able to supply either 230V or 115V. In wet zones, they must contain an isolation transformer compliant with BS 3535.


Soviet plug (6 A/250 V ungrounded)

The Soviet plug, still widely used in modern Russia, has pin dimensions and spacing equal to the Europlug, but lacks the insulation sleeves. It has a round body like the French type E or flat body with a round base like CEE7/17. The round base has no notches. The pins are parallel and do not converge. The body is made of fire resistant thermoset plastic.

There were also moulded rubber plugs available similar to CEE7/17, but with a round base without any notches. They could be altered to fit a type E or F socket by cutting notches with a sharp knife.

Europlug in Russian popular culture

In Russia "Europlug" (as pronounced in English), is always called a "conventional" plug, along with the Soviet plug. "Evrovilka" ("Евровилка", which means "Europlug" in the Russian language) almost always refers to the Schuko plug.


Unearthed socket compatible with both Schuko and French plugs
Variations in sockets

Type C sockets have no ground provisions and consequently have been phased out in some countries. For example, in Germany, ungrounded outlets are rare, found only in very old installations, whereas in the Netherlands they are common in "dry areas" such as in bedrooms or living rooms. Standards also vary between countries as to whether child-resistant shutters are required. Depending on the country and the age of the socket these sockets may have 4.0 or 4.8mm receptacles. The latter accept type E and F plugs in addition to type C, though without ground connection. Countries using the type E or F standards vary in whether ungrounded type C outlets are still permitted in environments where the need for grounding is less critical. Adaptors and trailing sockets and power strips designed to accept only Europlugs with 4 mm (0.157 in) pins may also have plastic barriers in place to prevent CEE 7/17, Schuko or French plugs from entering.

Type D

BS 546 (United Kingdom, 5 A/250 V grounded), equivalent to IA6A3 (India), rated at 6A / 250V
D Plug

India and Pakistan have standardised on a plug which was originally defined in British standard BS 546. It has three large round pins in a triangular pattern. The BS 546 standard is also used in parts of the Middle East (Kuwait, Qatar) and parts of Asia and South East Asia that were electrified by the British. This type was also previously used in South Africa, but has been phased out in favour of the 15 A version there. Similarly, in Ghana, Kenya and Nigeria, the plug has been mostly replaced by the British 3-pin (Type G). This 5 A plug, along with its smaller 2 A cousin, is sometimes used in the UK for centrally switched domestic lighting circuits, in order to distinguish them from normal power circuits.

BS 546 (United Kingdom, 15 A/250 V grounded), equivalent to IA16A3 (India) & SABS 164 (South Africa), rated at 16A / 250V
M Plug

This plug is sometimes referred to as type M, but it is in fact merely the 15 A version of the plug above, though its pins are much larger at 7.05 by 21.1 mm (0.278 by 0.831 in). Live and neutral are spaced 1 in (25.4 mm) apart, and earth is 1+18 in (28.58 mm) away from each of them. Although the 5 A version is standard in India, Pakistan, Sri Lanka, Nepal and Namibia, the 15 A version is also used in these countries for larger appliances. Some countries like South Africa use it as the main domestic plug and socket type, where sockets always have an on–off switch built into them. Type M is still commonly found in installations in Hong Kong and Botswana, alongside type G. The Type M was almost universally used in the UK and Ireland for indoor dimmable theatre and architectural lighting installations, but there is now a widespread move to using CEE 16 A industrial sockets in new installations. It was also often used for non-dimmed but centrally controlled sockets within such installations. The main reason for doing this is that fused plugs, while convenient for domestic wiring (as they allow 32 A socket circuits to be used safely), are not convenient if the plugs and sockets are in hard-to-access locations (like lighting bars) or if using chains of extension cords since it is hard to figure out which fuse has blown. Both of these situations are common in theatre wiring. This plug is also widely used in Israel, Singapore and Malaysia for air conditioners and clothes dryers.

Type E

French socket
French plug
CEE 7/5 (French type E)

France, Belgium, Poland, Czech Republic, Slovakia and some other countries have standardized on a socket which is not compatible with the CEE 7/4 socket (type F) standard in Germany and other continental European countries. The reason for incompatibility is that grounding in the E socket is done by a round male pin permanently mounted in the socket. Sockets are installed with the earth pin upwards. Although the plug is polarised, there is no universally observed standard for connecting the live and neutral. The plug itself is round with two round pins measuring 4.8 by 19 mm (0.189 by 0.748 in), spaced 19 mm (0.748 in) apart and a hole for the socket's ground pin. It will accept Europlug (type C) and CEE 7/17 plugs.

Like type F plug below, this plug will fit some other types of socket either easily or with force. However, there will be no ground connection with such sockets, and in some cases forcing the plug may damage the socket.

Child-resistant outlet shutters are required by French and Belgian standards, though are not required in all countries where this type is used.

The type has been authorised in Denmark since 1 July 2008, but sockets of this kind are not yet common.


Type F

CEE 7/4 (German "Schuko" 16 A/250 V grounded)
Schuko plug and socket

The type F plug, defined in CEE 7/4 and commonly called a "Schuko plug", is like type E except that it has two grounding clips on the sides of the plug instead of a female ground contact. The Schuko connection system is symmetrical and unpolarised by design, allowing live and neutral to be reversed. The socket also accepts Europlugs and CEE 7/17 plugs. It supplies up to 16 Amperes. It is used in Austria, Bulgaria, Chile, Croatia, Estonia, Finland, Germany, Greece, Hungary, Iceland, Indonesia, Latvia, Luxembourg, the Netherlands, Norway, Portugal, Romania, Serbia, Slovenia, South Korea, Spain, Sweden and Turkey.

"Schuko" is an abbreviation for the German word Schutzkontakt, which means "Protective (that is, grounded) contact".

Some countries – notably Norway and Sweden – require child-proof outlet shutters; the German Schuko standard does not have this requirement.

Gost 7396 (Russian 10 A/250 V grounded)

Russian Standard Gost 7396 defines a plug and receptacle similar to the Schuko, but with smaller pins of 4 mm (0.157 in) diameter, rated at 10 amps. A Gost 7396 will fit a Schuko receptacle, but the reverse is not possible since the Schuko and CEE 7/17 plugs pins are too large. This socket also accepts Europlugs.

Type E / F hybrid

CEE 7/7 plug
CEE 7/7 (French/German 16 A/250 V grounded)

In order to bridge the differences between sockets E and F, the CEE 7/7 plug was developed. It is polarised to prevent the live and neutral connections from being reversed when used with a type E outlet, but allows polarity reversal when inserted into a type F socket. The plug is rated at 16 A. It has grounding clips on both sides to connect with the CEE 7/4 socket and a female contact to accept the grounding pin of the type E socket. It's also used in Spain and Portugal. Currently, when appliances are sold with type E/F plugs attached, the plugs are CEE 7/7 and non-rewirable. This means that the plugs are now identical between countries like France and Germany, but the sockets are different.

Type G

BS 1363 (British 13 A/230-240 V 50 Hz grounded and fused), equivalent to IS 401 & 411 (Ireland), MS 589 (Malaysia) and SS 145 (Singapore), SASO 2203 (Saudi Arabia)
BS 1363

The British Standards 1363 plug.[16] This design is used not only in the United Kingdom, but also in Ireland, Sri Lanka, Bahrain, UAE, Qatar, Yemen, Oman, Jordan, Cyprus, Malta, Gibraltar, Botswana, Ghana, Hong Kong, Macau, Brunei, Malaysia, Singapore, Indonesia, Bangladesh, Kenya, Uganda, Malawi, Nigeria, Mauritius, Iraq, Kuwait, Tanzania, Zambia and Zimbabwe. BS 1363 is also standard in several of the former British Caribbean colonies such as Belize, Dominica, St. Lucia, Saint Vincent and the Grenadines and Grenada. It is also used in Saudi Arabia in 230 V installations although 110 V installations using the NEMA connector are more common.

This plug, commonly known as a "13-amp plug", is a large plug that has three rectangular prongs forming a triangle. Live and neutral are 18 mm (0.709 in) long, and spaced 22 mm (0.866 in) apart. 9 mm (0.354 in) of insulation at the trailing ends of the prongs prevents accidental contact with a bare connector while the plug is partially inserted. The earth prong is approximately 4 by 8 mm (0.157 by 0.315 in) and 23 mm (0.906 in) long.

The plug has a fuse inside. The fuse is required to protect the cord, as British wiring standards allow very high-current ring main circuits to the socket. Accepted practice is to choose the smallest standard fuse (3, 5 or 13 A) that will allow the appliance to function. Using a 13 A fuse on an appliance with thin cord is a fire hazard. The fuse is 1 in (25.40 mm) long, conforming to standard BS 1362. Sockets are required to be wired with neutral on the left and live on the right (viewed from the front of the socket) so that the fuse in the plug disconnects the live feed if it blows. The same convention is used for all British sockets connected directly to "mains" wiring.

UK wiring regulations (BS 7671) require sockets in homes to have shutters over the live and neutral connections to prevent the insertion of objects other than electric plugs. On most designs, these shutters are opened by the insertion of the longer earth prong. On some designs they are opened by the simultaneous insertion of the live and neutral prongs of the right shape and spacing. The effect of the shutters is to help prevent the use of plugs made to other standards, and to prevent children and others poking things into the dangerous connections. On plugs for Class II appliances that do not require an earth, the earth pin is often plastic and serves only to open the shutters and to enforce the correct orientation of live and neutral. It may be possible to open the shutters by putting a screwdriver blade into the earth socket, so as to insert a Type C Plug (but not the BS 4573 UK shaver) or other plug types, but this can be dangerous for such plugs will not have a fuse and will often not fit properly.

BS 1363 plugs and sockets started appearing in 1946 and BS 1363 was first published in 1947. By the end of the 1950s, it had replaced the earlier type D BS 546 in new installations, and by the end of the 1960s, most earlier type D installations had been rewired to BS 1363 standards. Outlets usually include switches on the live side for convenience and safety.

Type H

Two Israeli plugs and one socket. The left plug is the old standard, the one on the right is the 1989 revision.
SI 32 (Israeli 16 A/250 V grounded)

This plug, defined in SI 32 (IS16A-R), is unique to Israel and is incompatible with all other sockets. It has three flat pins to form a Y-shape. Live and neutral are spaced 19 mm (0.75 in) apart. The Type H plug is rated at 16A but in practice the thin flat pins can cause the plug to overheat when connecting large appliances.[citation needed] In 1989, the standard was revised to use three round 4 mm (0.157 in) pins in the same locations. Sockets made since 1989 accept both flat and round pins for compatibility with both old and new plugs. This also allows the Type H socket to accommodate the type C plugs used in Israel for non-earthed appliances. Older sockets, from about the 1970s, have both flat and round holes for live and neutral in order to accept both Type C and Type H plugs. As of 2008, type H sockets which accept only old-style type H plugs are very rare in Israel.

This plug is also used in the areas controlled by the Palestinian National Authority in the West Bank and all of the Gaza Strip.

Thai 3 pin plug TIS166-2549 (2006)

Thai multi-standard 3-pin sockets (like that shown below) safely accept unpolarised type A, B and C plugs, and also a 3 round-pin plug similar to the Israeli plug.[17]


Type I

Australasian switched 3-pin dual power point (socket)
AS/NZS 3112 (Australasian 10 A/240 V)
American patent filed in 1915 for a 3 prong grounding outlet, this example looks like the Type I.

This plug, used in Australia, New Zealand, Fiji, Argentina and Papua New Guinea, has a grounding pin, and two flat current-carrying pins forming an upside down V-shape.[18] The flat blades measure 6.5 by 1.6 mm (0.256 by 0.063 in) and are set at 30° to the vertical at a nominal pitch of 13.7 mm (0.539 in). Australian and New Zealand wall sockets almost always have switches on them for extra safety, as in the UK. An unearthed version of this plug with two angled power pins but no earthing pin is used with small double-insulated appliances, but the power (wall) outlets always have three pins, including a ground pin.

There are several AS/NZS 3112 plug variants,[19] including one with a wider ground pin used for devices drawing up to 15 amps; sockets supporting this pin will also accept 10 A plugs. There is also a 20 A variant, with all three pins oversized, and 25 and 32 A variants, with the 20A larger pins and the earthing pin forming an inverted "L" for the 25A and a horizontal "U" for the 32 A. These sockets accept plugs of equal or of a lower current capacity, but not of higher capacity. For example, a 10 A plug will fit all sockets but a 20 A plug will fit only 20, 25 and 32 A outlets).

Australasia's standard plug/socket system was originally codified as standard C112 (floated provisionally in 1937, and adopted as a formal standard in 1938), which was superseded by AS 3112 in 1990. As of 2005, the latest major update is AS/NZS 3112:2004, which mandated insulated pins[20] by 2005. However, equipment and cords made before 2003 can still be used.

Chinese sockets accepting plug types A, C (upper) and I (lower, standard)
CCC Mark
CPCS-CCC (Chinese 10 A/250 V)

Although the pins on the Chinese plug are 1 mm (0.039 in) longer, the Australasian plug can be used with mainland Chinese socket. The standard for Chinese plugs and sockets is set out in GB 2099.1–1996 and GB 1002–1996. As part of China's commitment for entry into the WTO, the new CPCS (Compulsory Product Certification System) has been introduced, and compliant Chinese plugs have been awarded the CCC Mark by this system. The plug is three wire, earthed, rated at 10 A, 250 V and used for Class 1 applications.

In China, the sockets are installed upside-down relative to the Australasian ones.

China also uses American/Japanese "Type A" sockets and plugs for Class-II appliances. However, the voltage across the pins of a Chinese socket will always be 220, no matter what the plug type.

IRAM 2073 (Argentinian 10 A/250 V)

The Argentinian plug is a three-wire earthed plug rated at 10 A, 250 V defined by IRAM and used in Class 1 applications in Argentina and Uruguay.

This plug is similar in appearance to the Australasian and Chinese plugs. The pin length is same as the Chinese version. The most important difference from the Australasian plug is that the Argentinian plug is wired with the live and neutral contacts reversed.


Type J

regular Type J plug and covered socket
Type J plugs and non-SEV 1011 socket
SEV 1011 (Swiss 10 A/250 V)

Switzerland has its own standard which is described in SEV 1011. (ASE1011/1959 SW10A-R) This plug is similar to the type C Europlug (CEE 7/16), except that it has an offset earth pin and the pin shanks are not insulated, so plugs partially inserted into non-recessed sockets present a shock hazard. Sockets used in kitchens, bathrooms and other wet areas are recessed, while those used elsewhere are not. Some plugs and adaptors have a tapered form and can be used in either environment, while others will fit only the non-recessed sockets. Swiss sockets accept Swiss plugs or Europlugs (CEE 7/16). There is also a non-earthed two-pin variant with the same pin shape, size, and spacing as the SEV 1011's live and neutral pins, but with a more flattened hexagonal form. It fits into round and hexagonal Swiss sockets and CEE 7/16 sockets, and is rated for up to 10 A.

A less-common variant has 3 square pins and is rated for 16 amps. Above 16 amps, equipment must either be hardwired to the electrical supply system with appropriate branch circuit protection, or connected to the mains with an appropriate high power industrial connector.


Type K (Danish standard)

Danish 107-2-D1, standard DK 2-1a, with round power pins and half round ground pin
Outlet for Danish computer equipment plug's tilted flattened pins and half round ground pin (mainly used in professional environment), standard DK 2-5a
Section 107-2-D1 (Danish 13 A/250 V earthed)

This Danish standard plug is described in the Danish Plug Equipment Section 107-2-D1 Standard sheet (SRAF1962/DB 16/87 DN10A-R). The plug is similar to the French type E except that it has an earthing pin instead of an earthing hole (and vice versa on the socket). This makes the Danish socket more unobtrusive than the French socket which is a cavity into the wall to protect the earthing pin from mechanical damage (and to protect from touching the live pins). The Danish standard provides for outlets to have child-resistant shutters.

The Danish socket will also accept the type C CEE 7/16 Europlug or type E/F CEE 7/17 Schuko-French hybrid plug. Type F CEE 7/4 (Schuko), type E/F CEE 7/7 (Schuko-French hybrid), and grounded type E French plugs will also fit into the socket but should not be used for appliances that need earth contact. The current rating on both plugs is 13A.

A variation (standard DK 2-5a) of the Danish plug is for use only on surge protected computer outlets. It fits into the corresponding computer socket and the normal type K socket, but normal type K plugs deliberately don't fit into the special computer socket. The plug is often used in companies, but rarely in private homes.

There is a variation for hospital equipment with a rectangular left pin, it is used for life support equipment.

Traditionally all Danish sockets were equipped with a switch to prevent touching live pins when connecting/disconnecting the plug. Today, sockets without switch are allowed, but then it is a requirement that the sockets have a cavity to prevent touching the live pins. However, the shape of the plugs generally makes it difficult to touch the pins when connecting/disconnecting.

Since the early 1990s grounded outlets have been required in all new electric installations in Denmark. Older outlets need not be grounded, but all outlets, including old installations, must be protected by ground-fault interrupters (HFI or HPFI in Danish) by 1 July 2008.

As of 1 July 2008, wall outlets for type E (French 2-pin, female earth) are permitted for installations in Denmark [21]. This was done because no electrical equipment sold to private users is equipped with a type K plug, and to break the monopoly of Lauritz Knudsen — the only company making type K sockets and plugs.

Sockets for the Schuko F type will not be permitted. The reason is that a large number of currently used Danish plugs (coincidentally made by the afore mentioned Lauritz Knudsen monopoly) will jam when inserted into a Schuko socket. This may cause damage to the socket. It may also result in a bad connection of the pins, with resultant risk of overheating and fire. Broken type F sockets are often seen in German hotels visited by Danes.[citation needed] Many international travel adapter sets sold outside Denmark match type C CEE 7/16 (Europlug) and type E/F CEE 7/7 (Schuko-French hybrid) plugs which can readily be used in Denmark.

Type L

23-16/VII plug with socket
Side by side comparison of Italian type L plugs rated 16 ampere (left) and 10 ampere (right).
An Italian installation carrying both Italian type L sockets (16 A on the left; 10 A on the right).
CEI 23-16/VII (Italian 10 A/250 V and 16 A/250 V)

The Italian earthed plug/socket standard, CEI 23-16/VII, includes two models rated at 10 A and 16 A that differ in contact diameter and spacing (see below for details). Both are symmetrical, allowing the live and neutral contacts to be inserted in either direction.

The double standard was initially adopted because in Italy, up to the second half of the twentieth century, the electric power used for lamps (Luce = lighting) and the one used for all other appliances (Forza = electromotive force; or Uso Promiscuo = general purpose) were sold at different fares, charged with different taxes, accounted with separated electricity meters, and sent on different wire lines that ended with different sockets.[22] Even though the two electric lines (and respective fares) were definitively unified during the summer of 1974[23] many houses kept twin wires and twin electricity meters for years thereafter. The two gauges for plugs and sockets thus became a de facto standard which is still in use today and has been standardized with CEI 23-16/VII. Older installations often have sockets that are limited to either the 10 A or the 16 A style plug, requiring the use of an adapter if the other gauge needs to be connected.

CEE 7/16 (type C) ungrounded Europlugs are also in common use; they are standardized in Italy as CEI 23-5 and fit most of the appliances with low current requirement and double insulation.

Appliances with CEE 7/7 Schuko-French plugs are often sold in Italy too; however not every socket will accept them since the pins of the CEE 7/7 Schuko-French plugs are thicker than the Italian ones. Adapters are cheap and commonly used to connect CEE 7/7 plugs to CEI 23-16/VII sockets, though the power rating may be mismatched (16A to 10A) and may lead to potentially unsafe connection in some cases.

CEI 23-16/VII (Italian 10 A/250 V)

The 10 ampere style extends CEE 7/16 by adding a central earthing pin of the same gauge. Thus, CEI 23-16-VII 10A sockets can accept CEE 7/16 Europlugs. This is the plug shown in the first picture.

CEI 23-16/VII (Italian 16 A/250 V)

The 16 ampere style looks like a magnified version of the 10 A style, identical in shape. However, the pins are 5 mm (0.197 in) thick (being 5 mm (0.197 in) thick in 10 A type), 8 mm (0.315 in) apart (while 5.5 mm (0.217 in) apart in 10 A type) and 7 mm (0.276 in) longer. The packaging of these plugs in Italy may claim they are a "North European" type. In the past they were also referred to as per la forza motrice[24] (for electromotive force, see above) or sometimes industriale (industrial), although the latter has never been a correct definition as factories used predominantly three-phase current and specialized connectors.

Twin-gauge or multi-type sockets
A bipasso socket (number 1) and an Italian adapted schuko (number 2 in the photo) in a modern installation.
An Italian VIMAR brand universale socket which can accept type A, C, E, F, E/F hybrids and both 10 A and 16 A L-type plugs.

Given that the plug with which appliances are fitted and sold varies, in modern installations in Italy (and in other countries where type L plugs are used) it is likely to find sockets that can accept more than one standard. The simpler type has a central round hole and two 8-shaped holes above and below. This design allows the connection of both styles of type L plugs (CEI 23-16/VII 10 A and 16 A) and the type C CEE 7/16 Europlug. The advantage of this socket style is its small, compact face. VIMAR brand claims to have patented this socket first in 1975[25] with their Bpresa model; however soon other brands started selling similar products mostly naming them with the generic term presa bipasso (twin-gauge socket) that is now of common use.

The current Italian standard provides for outlets to have child-resistant shutters.

A second, quite common type looks like a type F socket, but adds a central grounding hole. This design can accept CEE 7/7 (type E/F) plugs, in addition to type C and type L 10A plugs. Some of these sockets may also have 8-shaped holes to accept type L 16 A plugs as well. One drawback is that it is twice as large as a normal type L socket; also, 90° angled type L 16A plugs usually do not fit in these sockets.

Other types may push compatibility even further. The VIMAR-brand universale (all purpose) socket, for example, accepts CEE 7/7 (type E/F) plugs, type C plugs, both 10A and 16A type L plugs, and American/Japanese type A plugs as well.

Other countries

Outside of Italy, type L CEI 23-16/VII (Italian 10 A/250 V) plug is found in Syria, Libya, Ethiopia, Chile, Uruguay, various countries in North Africa, and occasionally in older buildings in Spain.


Type M

BS 546 (South African 15 A/250 V)

Type M is sometimes used to describe the 15 A version of the old British type D, used in South Africa and elsewhere.

North American oven and dryer outlets

NEMA 14–30

A 30 Ampere, 3 wire single-phase grounding receptacle is often used for electric clothes dryers. 240 Volts from the split phase system is used for the heating elements, and the motor and controls run on 120 volts.

NEMA 14–50

A 50 amp 3 wire single-phase grounding outlet is usually installed in kitchens and used for electric cooking ranges and ovens. As for dryers, lighting and motors run on 120 V and the main heating element is connected for 240 V.

Proposed common standard

A Brazilian socket for 20 A/250 V, meant for use with larger pins than 10A version
IEC 60906-1 (Brazilian 10 A and 20A /250 V - NBR 14136
2002)

In 1986, the International Electrotechnical Commission published IEC 60906-1, the specification for a plug that looks similar but is not identical to the Swiss (Type J) plug. This plug was intended to become one day the common standard for all of Europe and other regions with 230 V mains, but the effort to adopt it as a European Union standard was put on hold in the mid 1990s.[26] Brazil, which had used a mix of Europlug and NEMA plugs, adopted it as national standard NBR 14136 in 2001[27]. Since 2007, the adoption of this standard were optional for manufacturers, since most of Class 2 devices plugs (nearly 80%) fits with new standard. Since January 1, 2009, all installations had to comply with new standard, which caused some trouble, specially with some class 1 devices which used Type I plugs. Since January 1, 2010 new devices shall comply with the new regulation (end-user stores and resellers can sell equipments without adoption deadlines, but importers will not be allowed to bring nonconforming devices, nor will manufacturers be able to sell them locally). There are two types of sockets and plugs in this system: one for 10 A, with 4mm pin diameter and the other for 20 A, with a 4.8mm pin diameter, for heavier appliances, such as microwave ovens and HMVAC[28].

Comparison of plugs

Type Plug standard Power rating Grounded Polarised Fused
A NEMA 1–15 unpolarised 15A/125V No No No
NEMA 1–15 polarised 15A/125V No Yes No
JIS C 8303, Class II 15A/100V No No No
B NEMA 5–15 15A/125V Yes Yes No
NEMA 5–20 20A/125V Yes Yes No
JIS C 8303, Class I 15A/100V Yes Yes No
C CEE 7/16 (Europlug) 2.5A/250V No No No
CEE 7/17 16A/250V No No1 No
Soviet plug 6A/250V No No No
D BS 546 (2 pin) 2A/250V
5A/250V = BS 4573
No No No
BS 546 (3 pin) 2A/250V
5A/250V
15A/250V = SABS 164
30A/250V
Yes Yes No
E CEE 7/5 16A/250V Yes Yes No
F CEE 7/4 (Schuko) 16A/250V Yes No No
E+F CEE 7/7 16A/250V Yes Yes2 No
G BS 1363, IS 401 & 411, MS 589, SS 145 13A/230-240V Yes Yes Yes
H SI 32 16A/250V Yes Yes No
I AS/NZS 3112 10A/240V
20A/240V
25A/240V
32A/240V
Yes and
No
Yes No
CPCS-CCC 10A/250V Yes Yes No
IRAM 2073 10A/250V Yes Yes No
J SEV 1011 10A/250V
16A/250V
Yes Yes No
K Section 107-2-D1 13A/250V Yes Yes No
Thailand TIS 166 – 2549 13A/250V Yes Yes No
L CEI 23-16/VII 10A/250V
16A/250V
Yes No No
IEC 60906-1 (2 pin) 10A and 20A/250V No No No
IEC 60906-1 (3 pin) 10A and 20A/250V Yes Yes No

1 There are some CEE 7/17 plugs with special shape which are polarised when used with french socket of type E
2 Plug can only be inserted one way with French socket of type E, but lack of wiring convention means that the type is not polarised in practice

Multi-standard sockets

A standard grounded Thai outlet supporting European 2-pin plugs and earthed and unearthed American plugs

Sockets that take a variety of plug types can be found in various countries where market size or local market conditions make a specific plug standard impractical to implement. These socket accept plugs fitting various European, Asian and North American standards. Since many plug standards are also associated with corresponding voltages, multi-standard sockets do not safeguard against devices being damaged by the wrong voltage. This forces users to be aware of the voltage requirements of their appliances as well as the prevailing local voltage. Devices designed to adapt automatically to whatever voltage and frequency is supplied, and which don't require grounding, are generally safe to use with these sockets.

These sockets have one or more ground holes to allow 3-pin plugs. On properly wired circuits, the ground contact may be actually grounded; however, as with most other forms of plugs, they are not immune to poor wiring. They may also not provide grounding to all types of plugs, as is the case of Schuko or French plugs where the grounding pin that mates with the plug is part of the socket rather than the plug.

Adapters

A type M (15 A version of type D) travel adapter

To facilitate travelers' use of personal electric devices, adapters are available to permit the interconnection of normally-incompatible plugs and sockets. Such adapters overcome only the physical incompatibilities between plugs and sockets built to different standards; often a voltage converter is required for electrical compatibility.


Obsolete types

Old Spanish sockets

Spanish 3-prong plug&socket.jpg Spanish 3-prong adaptor.jpg
Left: Spanish three-prong plug and socket, with easily removable fuse)
Right: An adapter to allow types C and F to be inserted

Some older industrial buildings in Spain used sockets that took a particular type of plug which was rated for higher current and had two flat contacts and a round ground pin, somewhat similar in design to the ones found on American plugs but larger in size.

The live and neutral measure 9 by 2 mm (0.354 by 0.079 in), and are 30 mm (1.181 in) apart. All three pins are 19 mm (0.748 in) long, and the earth pin is a cylinder of 4.8 mm (0.189 in) diameter.

While the plug resembles an American connector, the two flat contacts are much wider apart than on a standard American plug, which will therefore not fit in these sockets.

No domestic appliances were ever sold with these plugs.

UK electric clock connector

British electric clock connector, 3-pin made by MK. Showing the rear of the plug with its 2 A fuse. Different manufacturers' clock connectors were generally not compatible.

Fused plugs and sockets of various proprietary and non-interchangeable types are found in older public buildings in the UK, where they are used to feed AC electric wall clocks. They are smaller than conventional socket outlets, commonly being made to fit BESA junction boxes, and are often of very low profile. Early types were available fused in both poles, later types fused in the live only and provided an earth pin. Most are equipped with a retaining screw or clip to prevent accidental disconnection. The prevalence of battery powered quartz controlled wall clocks has meant that this connector is rarely seen in new installations.

American "Type I"

Au-outlet.jpg Au-usa-plug.jpg
Left: American Type I duplex outlet
Right: Compatibility of American and Australian Type I plugs

The American electrical supply manufacturers Hubbell, Eagle, and possibly others made outlets and plugs that would match Type I plugs and sockets exactly. Type I connectors are used in Australia for 240 V service. These American outlets date back to at least 1915 (as seen in US Patent 1,179,728 filed in 1915[29]), antedating the American 3 prong Type B sockets and plugs. They were meant for appliances that needed grounding (120 V at 15 amps), and to be used in laundry rooms for washing machines and gas dryers (to power the motor). These did not become popular because American type A 2-prong plugs would not fit.

Split amperage/voltage ratings

Many older North American receptacles have two different amperage and voltage ratings, most commonly 10A 250V/15A 125V. This has to do with a peculiarity of the National Electrical Code from 1923 to the 1950s. Originally, receptacles were rated at 10A 250V, because the NEC limited lighting circuits to 10 amperes. In 1923, the code changed to allow lighting circuits to be fused at 15 amperes; however, the old rule still applied to circuits over 125 volts.[30] The higher voltages were rarely used for lighting and appliances. Most receptacles with this rating are of the "T-slot" type. This type of rating was phased out in the 1950s, and finally abolished in the 1960s with the adoption of the current NEMA standards.

Pre-NEMA "twist-lock" devices can sometimes be found with split 250V/600V ratings. These are also obsolete.

U.S. perpendicular outlet

Perpendicular slot duplex outlet
Perpendicular slot RP-2B outlet 10A 42V AC

Another obsolete outlet, made by Bryant, 125 V 15 A and 250 V 10 A rating. A NEMA 5–20 125 V 20 A or 6–20 250 V 20 A plug with a missing ground pin would fit this outlet, but a NEMA 2–20 plug is slightly too big to fit.

The upper slots as seen in the illustration connect to silver-coloured wiring screws on the upper side, and the lower slots connect to brass-coloured wiring screws on the lower side.

In Australia, the same or similar T-configuration sockets are used for DC power outlets, such as in stand-alone power systems (SAPS) or on boats.

In Soviet Union and now Russia this socket is commonly used for wiring in places where the voltage was lowered for safety purposes, like in schools, gas stations or in wet areas, rated 42 V 10 A AC. Such unusual connection was intended specifically to make the connection of standard higher-voltage equipment impossible.


U.S. Combination duplex outlet

Combo-outlet.jpg Tslotplug.jpg
Left: An extremely old "Nurpolian"-brand black parallel and tandem duplex outlet rated at 250 V 10 A (although this type was normally supplied with 120 V).

Right: T-slot duplex outlet.

The parallel and tandem outlet accepts normal parallel NEMA 1–15 plugs and also tandem NEMA 2–15 plugs. Both pair of receptacles are fed internally by the same supply.

A more recent and fairly common version of this type is the T-slot outlet, in which the locations of the tandem and the parallel slots were combined to create T-shaped slots. This version also accepts normal parallel NEMA 1–15 plugs and also tandem NEMA 2–15 plugs. Incidentally, a NEMA 5–20 (125 V, 20 A) or 6–20 (250 V, 20 A) plug with a missing ground pin would fit this outlet. This type is no longer available in retail shops since the 1960s.

U.K. Dorman & Smith (D&S)

D&S Socket

The D&S plugs and sockets were rated at 13 Amps and were one of the early competing types for use on ring main circuits. They were never popular in private houses but were widely deployed in prefabricated houses and council housing. The BBC also used them. D&S supplied the sockets to local authorities at very low cost, with the intention of making money out of the sales of plugs typically priced at 4 times the price of a type G plug. It is not known exactly when D&S ceased manufacturing the plugs and sockets but some local authorities continued to use them in new installations until the late 1950s. Many D&S sockets were still in use until the early 1980s, although the difficulty in obtaining plugs for them after around 1970 often forced their users to replace them with type G sockets. This generally violated local authority regulations on alterations to council housing.[citation needed] The D&S plug suffered from a serious design fault: the live pin was a fuse which screwed into the plug body and tended to come unscrewed on its own in use. A fuse that worked loose could end up protruding from the socket, electrically live and posing a shock hazard, when the plug was removed.

U.K. Wylex Plug

Wylex 13A Plug

The Wylex plugs and sockets were produced by Wylex Electrical Supplies Ltd. as a competitor to the type G and D&S sockets for use on ring main circuits. The plugs were available in both 5 A and 13 A versions, differing only by the widths of the live and neutral pins, and contained an internal fuse of the same rating as the plug. A plug had a central round earth pin and two flat pins, one on each side of the earth pin, for live and neutral. The two flat pins were slightly offset above and below the line cutting through the horizontal diameter of the earth pin. Wall sockets were rated at 13 Amps and took both 5 A and 13 A plugs. Many 13 A plugs had a socket on the back which took a 5 A plug, but would not take another 13 A plug because the slots for the live and neutral pins were narrower than those of the wall sockets, resulting in a stacked arrangement. Wylex sockets were used in council housing and public sector buildings, and for a short while in private housing. They were particularly popular in the Manchester area although they were installed throughout England, mainly in schools, university accommodation, and government laboratories. Wylex plugs and sockets continued to be manufactured for several years after type G sockets became standard and were commonly used by banks and in computer rooms during the 1960s and 70s for uninterruptible power supplies or "clean" filtered mains supplies. It is not known exactly when Wylex ceased manufacturing its plugs and sockets; however plugs were available in electrical shops of the Manchester area until the mid 1980s.

Lampholder plug

Two Italian bypass lampholder plugs with Edison screw mount. Left: early type (porcelain and brass, circa 1930); right: late type (black plastic, circa 1970).

A lampholder plug fits into the Bayonet cap or Edison screw socket of a lampholder in place of a light bulb and enables an electrical appliance to be powered from a wall or ceiling light fitting. They were commonly used during the 1920s to 1960s when wall sockets were scarce or nonexistent in many houses. Lampholder plugs were rarely fused.

Conventional practice in the U.K. is to protect lighting circuits with a 5 A fuse or circuit breaker, which makes it very easy to overload a lampholder and cause it to overheat by using a lampholder plug. Wiring regulations in the U.K. and some other countries no longer approve lampholder plugs because of the risks of overheating and fire.

In Italy, bypass lampholder plugs with Edison screw mount were in broad use until light wire cables were separated from general purpose wire cables (see type L paragraph for details) and some areas of the house (cellars, etc.) were commonly not provided with sockets.

Edison screw lampholder adaptors (for Type A plugs) are still easily found and commonly used in the Americas.

Old Greek sockets

Greek old three pin plugs.JPG Greek old three-pin 3-way adaptor plug.JPG
Greek old earthed standard adaptor plugs
Greek Old Earthed Standard Socket.jpg
Greek old earthed standard socket.

Called "Tripoliki" (τριπολικές) the 3 Pin round standard similar to type J and post-1989 type H, virtually abandoned by 1995.

Previous to the large-scale adoption of schuko plugs, this was the only way to use an earthed appliance.


Unusual types

NEMA 2–15 and 2–20

These ungrounded plugs with two flat parallel prongs are variants of the 1–15 but are intended to deliver 240 volts instead of 120. The 2–15 has coplanar current prongs (rotated 90° from ordinary American plugs), and is used for 240 V service at 15 amperes, while the 2–20 has the two current prongs rotated 90° relative to each other (one vertical, one horizontal) and is used for 240 V service at 20 amperes. NEMA 2 plugs and sockets are rare because they have been prohibited for household use in the United States and Canada for several decades. They are potentially hazardous since they have no ground or neutral, and in some cases plugs can be inserted into incorrect-voltage sockets. Prior to the adoption of the NEMA standard, a plug nearly identical to the 2–20 was used for 120 V at 20 A. A 2–20 plug would fit into 5–20 and 6–20 sockets, which supply different voltages.

Soviet adaptor plugs

Some appliances sold in Soviet Union had a flat unearthed plug with an additional pass-through socket on the top, allowing stacked arrangement of plugs. This design was very helpful, for the usual soviet flat had in 1960s very few wall sockets, but completely unsafe as the brass cylinders of secondary socket were uncovered at the ends (to unscrew them easily), recessed only for 3mm and provided bad contact because relied on secondary plug's bisected expanding pins. The pins of secondary plug (without insulation sleeves) could not be inserted into cylinders completely and were accessible through a 5mm gap between primary and secondary plugs.

U.K. Walsall Gauge plug

WG13 PICT6943.jpg WG13 PICT6945.jpg
Walsall Gauge 13 A plug (bottom) compared to regular BS 1363 plug

Unlike the standard BS 1363 plugs found in the U.K., the earth pin is on a horizontal axis and the live and neutral pins on a vertical axis. This style of plug/socket was used by the BBC, and is still in use on parts of the London Underground for low voltage power supply.

Italian Bticino brand Magic security connector

Bticino Magic 1.jpg Bticino Magic 2.jpg Bticino Magic 3.jpg
Left: Bticino Magic Security receptacle, detail.
Centre: assortment of Magic Security receptacles (in orange, the industrial three-phase type).
Right: assortment of Magic Security plugs.

This style of connector, produced by Italian brand Bticino, appeared in the 1960s and was intended as an alternative to the Europlug or type L connectors then in use[31]. The socket is an almost rectangular receptacle, with one or more lateral key pins and indents to prevent inverting the plug (it is polarised), or connecting plugs and sockets with different ampere ratings. At least four models were produced: three single-phase general purpose connectors rated respectively 10 A, 16 A and 20 A; plus a three-phase industrial connector rated 10 A; all of them have different key-pin positioning so plugs and sockets cannot be mismatched[32]. The socket is closed by a safety lid (bearing the word ‘’Magic’’ on it) which can be opened only with an even pressure on its surface, thus preventing the insertion of objects (except the plug itself) inside the socket. The contacts are blades positioned on both sides of the plug; the plug is energized only when it is inserted fully into the socket.

The obvious drawback of the system is that it is not compatible with europlugs. As household appliances were never sold fitted with these security plugs and the use of adapters would defeat all of the newly introduced safety features, once this system is adopted all standard plugs must be cut off and replaced with the appropriate security connector. However, the Magic security system had some success at first because its enhanced safety features appealed to customers; standard connectors of the day were considered not safe enough[31]. The decline of the system occurred when safety lids similar to the Magic type were developed (VIMAR Sicury[33]) and then applied to standard type L sockets by third brands and by Bticino itself.

In Italy, the system was never definitively abandoned and, though rarely seen today, is still marked as available in Bticino’s products catalogue[34].

In Chile, 10 [A] Magic connectors are commonly used for computer/laboratory power networks, as well as for communications or data equipment. This allows delicate electronics equipment to be connected to an independent circuit breaker, usually including a surge protector or an uninterruptible power supply backup. The different style of plug makes it more difficult for office workers to connect computer equipment to a standard unprotected power line, or to overload the UPS by connecting other office appliances.

In Iceland, Magic connectors were widely used in homes and businesses alongside Europlug and Schuko installations. Their installation in new homes was still quite common even in the late 1980s.

Single phase electric stove plugs and sockets

Power connector Legrand (400 V, 32 A)
Russian stove connectors rated for 250V 25A AC. Left: plug and socket. Center: Socket. Right: Plug.

The plugs and sockets used to power electric stoves from a single-phase line have to be rated for greater current values than ones for three-phase system because all the power has to be transferred through a single line. Electric stoves are often hardwired to the electrical supply system, connected to the mains with an appropriate high power industrial connector or with non-standard high power proprietary domestic connector (as some countries do not have wiring regulations for single-phase electric stoves). In Russia an electric stove can be often seen connected with an 25–32 Amps connector.

See also

References

  1. ^ Collins Essential English Dictionary 2nd Edition 2006: Power Point
  2. ^ Redesign of a power point socket
  3. ^ Hubbell (2006). "Hubbell History". Hubbell Incorporated. http://www.hubbell.com/history.htm. Retrieved 2006-10-10. 
  4. ^ Witte. "The Automobile Storage Battery Its Care and Repair". www.powerstream.com. http://www.powerstream.com/1922/battery_1922_WITTE/battery_WITTE.htm. Retrieved 2007-09-14. 
  5. ^ Crist. "Socket Tutorial". www.mosaicshades.com. http://www.mosaicshades.com/antique2005/sockets/index.htm. Retrieved 2007-09-14. 
  6. ^ German patent number DE 370538
  7. ^ U.S. Patent 1,672,067
  8. ^ U.S. Patent 1,672,067
  9. ^ a b "Electric Current Abroad" (PDF). U.S. Department of Commerce, International Trade Administration. 2002. http://www.ita.doc.gov/media/Publications/pdf/current2002FINAL.pdf. 
  10. ^ IEC/TR 60083, Plugs and socket-outlets for domestic and similar general use standardized in member countries of IEC, International Electrotechnical Commission (2006)
  11. ^ a b NEMA WD6, Dimensional requirements for plugs and receptacles
  12. ^ a b JIS C 8303-1993,Plugs and Receptacles for Domestic and Similar General Use,Japanese Standards Association (1993)
  13. ^ http://www.childoutletsafety.org/ Retrieved 2009 Jan 21
  14. ^ EN 50075 (1991), Specification for flat non-wirable two-pole plugs 2.5A 250V, with cord, for the connection of class II-equipment for household and similar purposes, European Committee for Standardization (CEN)
  15. ^ BS 4573 (1970), British Standard Specification for two-pin reversible plugs and shaver socket-outlets, British Standards Institution
  16. ^ BS 1363 (1995), 13 A plugs, socket-outlets and adaptors Specification for rewirable and non-rewirable 13 A fused plugs, British Standards Institute.
  17. ^ [1]
  18. ^ AS/NZS 3112:2004, Approval and test specification — Plugs and socket-outlets, Standards Australia and Standards New Zealand
  19. ^ "Australian Mains Plug Variants – AS/NZS 3112". Access Communications Pty Ltd. 2007-04-19. http://www.accesscomms.com.au/reference/AustMainsPlugVariants.htm. 
  20. ^ "Mains Plugs with Insulated Pins. Australian Standards AS/NZS3112:2000 & AS/NZS3112:2004 refer [sic"]. Access Communications Pty Ltd. 2007-04-19. http://www.accesscomms.com.au/reference/insulated-pins.htm. 
  21. ^ 5. udgave af Stærkstrømsbekendtgørelsen afsnit 107-2-D1 "Stikpropper og stikkontakter for danske systemer"
  22. ^ De Cesco G.: Acqua Luce Gas. Manuali pratici del far da sé. I Jolly bricolage. Fratelli Fabbri Editori, Milano, 1975. PP 56–57.
  23. ^ De Cesco G.: Acqua Luce Gas. Manuali pratici del far da sé. I Jolly bricolage. Fratelli Fabbri Editori, Milano, 1975. P 93.
  24. ^ De Cesco G.: Acqua Luce Gas. Manuali pratici del far da sé. I Jolly bricolage. Fratelli Fabbri Editori, Milano, 1975. PP 70–71.
  25. ^ La ricerca della sicurezza. Ma la ricerca continua. www.vimar.eu. Retrieved on 22 Jan 2009.
  26. ^ "International standardization of electrical plugs and sockets for domestic use". IEC. http://www.iec.ch/zone/plugsocket/ps_history.htm. 
  27. ^ NBR 14136:2002 – Plugues e tomadas para uso doméstico e análogo – Padronização (Plugs and socket-outlets for household use and similar purposes – Specification)
  28. ^ "Norma ABNT NBR 14136:2002" (in Portuguese). http://www.projetoderedes.com.br/artigos/artigo_norma_abnt_14136.php. 
  29. ^ http://patft.uspto.gov/netahtml/PTO/srchnum.htm and type in the patent number in the search box, then click "images"
  30. ^ Terrell Croft, Wiring for Light and Power, McGraw-Hill, 1924, pages 198–199
  31. ^ a b De Cesco G.: Acqua Luce Gas. Manuali pratici del far da sé. I Jolly bricolage. Fratelli Fabbri Editori, Milano, 1975. P 73.
  32. ^ De Cesco G.: Acqua Luce Gas. Manuali pratici del far da sé. I Jolly bricolage. Fratelli Fabbri Editori, Milano, 1975. P 75.
  33. ^ La ricerca della sicurezza. Il brevetto Sicury. www.vimar.eu. Retrieved on 12 Feb 2009.
  34. ^ Catalogo online. Installazione civile. www.professionisti.bticino.it. Retrieved on 12 Feb 2009.

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