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AC power plugs and sockets connect devices to mains electricity to supply them with electrical power. A plug is the connector attached to an electrically-operated device, often via a cable. A socket (also known as a receptacle or outlet) is fixed in place, often on the internal walls of buildings, and is connected to an AC electrical circuit. Inserting ("plugging in") the plug into the socket allows the device to draw power from this circuit.

Plugs and wall-mounted sockets for portable appliances became available in the 1880s, to replace connections to light sockets. A proliferation of types were subsequently developed for both convenience and protection from electrical injury. Electrical plugs and sockets differ from one another in voltage and current rating, shape, size, and connector type. Different standard systems of plugs and sockets are used around the world, and many obsolete socket types are still found in older buildings.

Coordination of technical standards has allowed some types of plug to be used across large regions to facilitate the production and import of electrical appliances and for the convenience of travellers. Some multi-standard sockets allow use of several types of plug. Incompatible sockets and plugs may be used with the help of adaptors, though these may not always provide full safety and performance.

Overview of connections

Single-phase sockets have two current-carrying connections to the power supply circuit, and may also have a third pin for a safety connection to earth ground. The plug is a male connector, usually with protruding pins that match the openings and female contacts in a socket. Some plugs also have a female contact, used only for the earth ground connection. Typically no energy is supplied to any exposed pins or terminals on the socket. In addition to the recessed contacts of the energised socket, plug and socket systems often have other safety features to reduce the risk of electric shock or damage to appliances.

History

When commercial electric power was first introduced in the 1880s, it was used primarily for lighting. Other portable appliances (such as vacuum cleaners, electric fans, smoothing irons, and curling-tong heaters) were connected to light-bulb sockets.

As early as 1885 a two-pin plug and wall socket format was available on the British market. By about 1910 the first three-pin earthed (grounded) plugs appeared. Over time other safety improvements were gradually introduced to the market. The earliest national standard for plug and wall socket forms was set in 1915.

Safety features

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Protection from accidental contact

Designs of plugs and sockets have gradually developed to reduce the risk of electric shock and fire. Plugs are shaped to prevent bodily contact with live parts. Sockets may be recessed and plugs designed to fit closely within the recess to reduce risk of a user contacting the live pins. Contact pins may be sheathed with insulation over part of their length, so as to reduce exposure of energized metal during insertion or removal of the plug. Sockets may have automatic shutters to stop foreign objects from being inserted into energized contacts. Sockets are often set into a surround which prevents accidental contact with the live wires in the wall behind it. Some also have an integrated cover (e.g. a hinged flap) covering the socket itself when not in use, or a switch to turn off the socket.

Overcurrent protection

Some plugs have a built-in fuse which breaks the circuit if too much current is passed.

Earthing (grounding)

A third contact for a connection to earth is intended to protect against insulation failure of the connected device. Some early unearthed plug and socket types were revised to include an earthing pin or phased out in favour of earthed types. The plug is often designed so that the earth ground contact connects before the energized circuit contacts.

The assigned IEC appliance class is governed by the requirement for earthing or equivalent protection. Class I equipment requires an earth contact in the plug and socket, while Class II equipment is unearthed and protects the user with double insulation.

Polarisation

Where a "neutral" conductor exists in supply wiring, polarisation of the plug can improve safety by preserving the distinction in the equipment. For example, appliances may ensure that switches interrupt the line side of the circuit, or can connect the shell of a screw-base lampholder to neutral to reduce electric shock hazard. In some designs, polarised plugs cannot be mated with non-polarised sockets. In NEMA 1 plugs, for example, the neutral blade is slightly wider than the hot blade, so it can only be inserted one way. Wiring systems where both circuit conductors have a significant potential with respect to earth do not benefit from polarised plugs.

Voltage rating of plugs and power cords

Plugs and power cords have a rated voltage and current assigned to them by the manufacturer. Using a plug or power cord that is inappropriate for the load may be a safety hazard. For example, high-current equipment can cause a fire when plugged into an extension cord with a current rating lower than necessary. Sometimes the cords used to plug in dual voltage 120 V / 240 V equipment are rated only for 125 V, so care must be taken by travellers to use only cords with an appropriate voltage rating.

Extension

Various methods can be used to increase the number or reach of sockets.

Extension cords

Extension cords (extension leads) are used for temporary connections when a socket is not within convenient reach of an appliance's power lead. This may be in the form of a single socket on a flexible cable or a power strip with multiple sockets. A power strip may also have switches, surge voltage protection, or overcurrent protection.

Multisocket adaptors

• A French CEE 7 adaptor
• An old US multisocket adaptor

Multisocket adaptors (or "splitters") allow the connection of two or more plugs to a single socket. They are manufactured in various configurations, depending on the country and the region in which they are used, with various ratings. This allows connecting more than one electrical consumer item to one single socket and is mainly used for low power devices (TV sets, table lamps, computers, etc.). They are usually rated at 6 A 250 V, 10 A 250 V, or 16 A 250 V. This is the general rating of the adaptor, and indicates the maximum total load in amps, regardless of the number of sockets used (for example, if a 16 A 250 V adaptor has four sockets, it would be fine to plug four different devices into it that each consume 2 A as this represents a total load of only 8 A, whereas if only two devices were plugged into it that each consumed 10 A, the combined 20 A load would overload the circuit). In some countries these adaptors are banned and are not available in shops, as they may lead to fires due to overloading them or can cause excessive mechanical stress to wall-mounted sockets. Adaptors can be made with ceramic, Bakelite, or other plastic bodies.

Cross-compatibility

Universal sockets

• A so-called "universal socket", which meets no official standard but is intended to accept a number of different plug types
• An earthed Thai socket that appears to comply with figure 4 of TIS 166-2549. Although it may accept NEMA plugs, the Thai voltage is 220 V and thus is electrically incompatible with devices designed only for 110 V.
• Chinese dual socket accepting both unearthed two-pin (upper) and earthed three-pin (lower) plugs

"Universal" or "multi-standard" sockets are intended to accommodate plugs of various types. In some jurisdictions, they violate safety standards for sockets.

Safety advocates, the United States Army, and a manufacturer of sockets point out a number of safety issues with universal socket and adaptors, including voltage mismatch, exposure of live pins, lack of proper earth ground connection, or lack of protection from overload or short circuit. Universal sockets may not meet technical standards for durability, plug retention force, temperature rise of components, or other performance requirements, as they are outside the scope of national and international technical standards.

A technical standard may include compatibility of a socket with more than one form of plug. The Thai dual socket is specified in figure 4 of TIS 166-2549 and is designed to accept Thai plugs, and also Type A, B, and C plugs. Chinese dual sockets have both an unearthed socket complying with figure 5 of GB 1002-2008 (both flat pin and 4.8 mm round pin), and an earthed socket complying with figure 4 of GB 1002-2008. Both Thai and Chinese dual sockets also physically accept plugs normally fitted to 120 V appliances (e.g. 120 V rated NEMA 1-15 ungrounded plugs). This can cause an electrical incompatibility, since both states normally supply residential power only at 220 V.

Swappable cables and plugs

Commonly, manufacturers provide an IEC 60320 inlet on an appliance, with a detachable power cord (mains flex lead) and appropriate plug in order to avoid manufacturing whole appliances, with the only difference being the type of plug. Alternatively, the plug itself can often be swappable using standard or proprietary connectors.

Travel adaptors

Adaptors between standards are not included in most standards, and as a result they have no formal quality criteria defined. Physical compatibility does not ensure that the appliance and socket match in frequency or voltage. Adaptors allow travellers to connect devices to foreign sockets, but do not change voltage or frequency. A voltage converter is required for electrical compatibility in places with a different voltage than the device is designed for. Mismatch in frequency between supply and appliances may still cause problems even at the correct voltage. Some appliances have a switch for the selection of voltage.

Standard types in present use

The plugs and sockets used in a given area are regulated by local governments.

The International Electrotechnical Commission (IEC) maintains a guide with letter designations for generally compatible types of plugs, which expands on earlier guides published by the United States Department of Commerce. This is a de facto naming standard and guide to travellers. Some letter types correspond to several current ratings or different technical standards, so the letter does not uniquely identify a plug and socket within the type family, nor guarantee compatibility. Physical compatibility of the plug and socket does not ensure correct voltage, frequency, or current capacity. Not all plug and socket families have letters in the IEC guide, but those that have are noted in this article, as are some additional letters commonly used by retail vendors.

In Europe, CENELEC publishes a list of approved plug and socket technical standards used in the member countries.

Argentina IRAM 2073 and 2071 (Type I)

• Argentine 1996 power plug arrangement

The plug and socket system used in Class 1 applications in Argentina is defined by IRAM standards. These two standards are; IRAM 2073 "Two pole plugs with earthing contact for domestic and similar purposes, rated 10 A and 20 A, 250 V AC" and IRAM 2071 "Two pole socket – outlets with earthing contact for 10 A and 20 A, 250 V AC., for fixed installations." The plug and socket system is similar in appearance to the Australian and Chinese plugs. It has an earthing pin and two flat current-carrying pins forming an inverted V-shape (120°). The flat pins for the 10 A version measure 6.25 by 1.55 mm (0.246 by 0.061 in) and 8.0 by 1.9 mm (0.315 by 0.075 in) for the 20 A version, and are set at 30° to the vertical at a nominal pitch of 7.92 mm (0.312 in). The pin length is the same as in the Chinese version. The earthing pin length is 21.4 mm (0.843 in) for the 10 A version and 21.8 mm (0.858 in) for the 20 A version. On the plugs, the pole length is 18.2 mm (0.717 in) for the 10 A version and 17.8 mm (0.701 in) for the 20 A version.

The most important difference from the Australian plug is that the Argentine plug is wired with the live and neutral contacts reversed.

In Brazil, similar plugs and sockets are still commonly used in old installations for high-power appliances like air conditioners, dishwashers, and household ovens. Although being often called "Argentine plug," it is actually based on the American NEMA 10-20 standard, and is incompatible with Argentine IRAM plugs. Since Brazil adopted the NBR 14136 standard which includes a 20 A version, the original motivation to use the NEMA 10-20 plug has ceased to exist.

Australian/New Zealand standard AS/NZS 3112 (Type I), used in Australasia

• Australasian switched three-pin (10 A) dual socket outlet, the most commonly found variant

• Standard Australian 10 A power plug with insulated pins

• 10 A, 15 A, 20 A, 25 A, and 32 A single-phase sockets. Each socket accepts plugs of equal or lesser current rating.

This Australian/New Zealand standard is used in Australia, New Zealand, Fiji, Tonga, Solomon Islands, and Papua New Guinea. It defines a plug with an earthing pin, and two flat current-carrying pins which form an inverted V-shape. The flat pins 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 (locally often referred to as power points) 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 double-insulated appliances, but the sockets always include an earth contact.

There are several AS/NZS 3112 plug variants, including ones with larger or differently shaped pins used for devices drawing 15, 20, 25 and 32 A. These sockets accept plugs of equal or lower current rating, but not higher. For example, a 10 A plug will fit all sockets but a 20 A plug will fit only 20, 25 and 32 A sockets. In New Zealand, PDL 940 "tap-on" or "piggy-back" plugs are available which allow a second 10 A plug to be fitted to the rear of the plug. In Australia these piggy-back plugs are now available only on pre-made extension leads.

Australia'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 based on a design patented by Harvey Hubbell and was superseded by AS 3112 in 1990. The requirement for insulated pins was introduced in the 2004 revision. The current version is AS/NZS 3112:2011, Approval and test specification – Plugs and socket-outlets.

Brazilian standard NBR 14136 (Type N)

• Brazilian 10 ampere socket and plugs
• Brazilian 20 ampere socket

Brazil, which had been using mostly Europlugs, and NEMA 1-15 and NEMA 5-15 standards, adopted a (non-compliant) variant of IEC 60906-1 as the national standard in 1998 under specification NBR 14136 (revised in 2002). These are used for both 220-volt and 127-volt regions of the country, despite the IEC 60906-2 recommendation that NEMA 5-15 be used for 120 V connections. There are two types of sockets and plugs in NBR 14136: one for 10 A, with a 4.0 mm pin diameter, and another for 20 A, with a 4.8 mm pin diameter. This differs from IEC 60906-1 which specifies a pin diameter of 4.5 mm and a rating of 16 A. NBR 14136 does not require shutters on the apertures, a further aspect of non-compliance with IEC 60906-1. NBR 14136 was not enforced in that country until 2007, when its adoption was made optional for manufacturers. It became compulsory on 1 January 2010.

Few private houses in Brazil have an earthed supply, so even if a three-pin socket is present it is not safe to assume that all three terminals are actually connected. Most large domestic appliances were sold with the option to fit a flying earth tail to be locally earthed, but many consumers were unsure how to use this and so did not connect it. The new standard has an earth pin, which in theory eliminates the need for the flying earth tail.

British and compatible standards

BS 546 and related types (Type D and M)

BS 546, "Two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors for AC (50-60 Hz) circuits up to 250 V" describes four sizes of plug rated at 2 A, 5 A (Type D), 15 A (Type M) and 30 A. The plugs have three round pins arranged in a triangle, with the larger top pin being the earthing pin. The plugs are polarised and unfused. Plugs are non-interchangeable between current ratings. Introduced in 1934, the BS 546 type has mostly been displaced in the UK by the BS 1363 standard. According to the IEC, some 40 countries use Type D and 15 countries use Type M. Some, such as India and South Africa, use standards based on BS 546.

• BS 1363 sockets
• BS 1363 plug with fuse compartment visible

BS 1363 (Type G)

BS 1363 "13 A plugs, socket-outlets, adaptors and connection units" is the main plug and socket type used in the United Kingdom. According to the IEC it is also used in over 50 countries worldwide. Some of these countries have national standards based on BS 1363, including: Bahrain, Hong Kong, Ireland, Cyprus, Malaysia, Malta, Saudi Arabia, Singapore, Sri Lanka, and UAE.

This plug has three rectangular pins forming an isosceles triangle. The BS 1363 plug has a fuse rated to protect its flexible cord from overload and consequent fire risk. Modern appliances may only be sold with a fuse of the appropriate size pre-installed.

BS 4573 (UK shaver)

The United Kingdom, Ireland, and Malta use the BS 4573 two-pin plug and socket for electric shavers and toothbrushes. The plug has insulated sleeves on the pins. Although similar to the Europlug Type C, the diameter and spacing of the pins are slightly different and hence it will not fit into a Schuko socket. There are, however, two-pin sockets and adaptors which will accept both BS 4573 and Europlugs.

CEE 7 standard

The International Commission on the Rules for the Approval of Electrical Equipment (IECEE) was a standards body which published Specification for plugs and socket-outlets for domestic and similar purposes as CEE Publication 7 in 1951. It was last updated by Modification 4 in March 1983. CEE 7 consists of general specifications and standard sheets for specific connectors.

Standard plugs and sockets based on two round pins with centres spaced at 19 mm are in use in Europe, most of which are listed in IEC/TR 60083 "Plugs and socket-outlets for domestic and similar general use standardized in member countries of IEC." EU countries each have their own regulations and national standards; for example, some require child-resistant shutters, while others do not. CE marking is neither applicable nor permitted on plugs and sockets.

CEE 7/1 unearthed socket and CEE 7/2 unearthed plug

CEE 7/1 unearthed sockets accept CEE 7/2 round plugs with 4.8 by 19 mm (0.189 by 0.748 in) pins. Because they have no earth connections they have been or are being phased out in most countries. Some countries still permit their use in dry areas, while others allow their sale for replacements only. Older sockets are so shallow that it is possible to accidentally touch the live pins of a plug. CEE 7/1 sockets also accept CEE 7/4, CEE 7/6 and CEE 7/7 plugs without providing an earth connection. The earthed CEE 7/3 and CEE 7/5 sockets do not allow insertion of CEE 7/2 unearthed round plugs.

CEE 7/3 socket and CEE 7/4 plug (German "Schuko"; Type F)

The CEE 7/3 socket and CEE 7/4 plug are commonly called Schuko, an abbreviation for Schutzkontakt, Protective contact to earth ("Schuko" itself is a registered trademark of a German association established to own the term). The socket has a circular recess with two round holes and two earthing clips that engage before live pin contact is made. The pins are 4.8 by 19 mm (0.189 by 0.748 in). The Schuko system is unpolarised, allowing live and neutral to be reversed. The socket accepts Europlugs and CEE 7/17 plugs and also includes CEE 7/7. It is rated at 16 A. The current German standards are DIN 49441 and DIN 49440. The standard is used in Germany and several other European countries and on other continents. Some countries require child-proof socket shutters; the DIN 49440 standard does not have this requirement.

The plug is used in most or many countries of Europe, Asia, and Africa, as well as in the countries of South Korea, Peru, Chile and Uruguay. The few European countries not using it at all are Belgium, Czech Republic, Cyprus, Ireland, Liechtenstein, Switzerland, and the UK, or not using it predominantly are Denmark, Faroe Island, France, Italy, Monaco, San Marino, Slovakia.

CEE 7/5 socket and CEE 7/6 plug (French; Type E)

• French socket (CEE 7/5)
• Rewireable French plug (CEE 7/6)
• Hybrid CEE 7/7 plug

French standard NF C 61-314 defines the CEE 7/5 socket and CEE 7/6 plug, (and also includes CEE 7/7, 7/16 and 7/17 plugs). The socket has a circular recess with two round holes. The round earth pin projecting from the socket connects before the energized contacts touch. The earth pin is centred between the apertures, offset by 10 mm (0.394 in). The plug has two round pins measuring 4.8 by 19 mm (0.189 by 0.748 in), spaced 19 mm (0.748 in) apart and with an aperture for the socket's projecting earth pin. This standard is also used in Belgium, Poland, the Czech Republic, Slovakia and some other countries.

Although the plug is polarised, CEE 7 does not define the placement of the live and neutral, and different countries have conflicting standards for that. For example, the French standard NF C 15-100 requires live to be on the right side, while Czech standard ČSN 33 2180 requires live to be on the left side of a socket. Thus, a French plug when plugged into a Czech socket (or a Czech plug when plugged into a French socket) will always have its polarity reversed, with no way for the user to remedy this situation apart from rewiring the plug. One approach for resolving this situation is taken in Poland, where CEE 7/5 sockets are typically installed in pairs, the upper (upside-down) one having the "French" polarity and the lower one having the "Czech" polarity, so that the user can choose what to plug where.

CEE 7/4 (Schuko) plugs are not compatible with the CEE 7/5 socket because of the round earthing pin permanently mounted in the socket; CEE 7/6 plugs are not compatible with Schuko sockets due to the presence of indentations on the side of the recess, as well as the earth clips. CEE 7/7 plugs have been designed to solve this incompatibility by being able to fit in either type of socket.

Sales and installations of 7/5 sockets are legally permitted in Denmark since 2008, but the sockets are hard to find in physical stores, and installation is exceedingly rarely performed.

CEE 7/7 plug (compatible with E and F)

The CEE 7/7 plug fits in either French or Schuko sockets. It is rated at 16A and looks similar to CEE 7/4 plugs, but with earth contacts to fit both CEE 7/5 sockets and CEE 7/3 ones. It is polarised when used with a French-style CEE 7/5 socket, but can be inserted in two ways into a CEE 7/3 socket. However, with the French socket it is not specified whether the live connection is on the left or right, as this can vary between countries.

Earthed appliances are typically sold fitted with non-rewireable CEE 7/7 plugs attached, though rewireable versions are also available. This plug can be inserted into a Danish Type K socket, but the earth contact will not connect.

CEE 7/16 plugs

The CEE 7/16 unearthed plug is used for unearthed appliances. It has two round 4 by 19 mm (0.157 by 0.748 in) pins, rated at 2.5 A. There are two variants.

CEE 7/16 Alternative I

Alternative I is a round plug with cutouts to make it compatible with CEE 7/3 and CEE 7/5 sockets. (The similar-appearing CEE 7/17 has larger pins and a higher current rating.) This alternative is seldom used.

CEE 7/16 Alternative II "Europlug" (Type C)

Alternative II, popularly known as the Europlug, is a flat 2.5 A-rated plug defined by Cenelec standard EN 50075 and national equivalents. The Europlug is not rewirable and must be supplied with a flexible cord. It can be inserted in either direction, so line and neutral are connected arbitrarily. To improve contact with socket parts the Europlug has slightly flexible pins which converge toward their free ends.

There is no socket defined to accept only the Europlug. Instead, the Europlug fits a range of sockets in common use in Europe. These sockets include CEE 7/1, CEE 7/3 (German/"Schuko") and CEE 7/5 (French). Most Israeli, Swiss, Danish and Italian sockets were designed to accept pins of various diameters, mainly 4.8 mm, but also 4.0 mm and 4.5 mm, and are usually fed by final circuits with either 10 A or 16 A overcurrent protection devices.

Although the standard does not permit extension cables and does not define any socket-outlets, unauthorized extension cables and sockets are manufactured.

UK shaver sockets are designed to accept BS 4573 shaver plugs while also accepting Europlugs. In this configuration, the connection supply is only rated at 200 mA. It is not permissible within the UK for the shaver socket to be fitted and used for a higher rated current draw than the 200 mA maximum.

The Europlug is also used in parts of the Middle East, Africa, South America, and Asia.

CEE 7/17 unearthed plug

This is a round plug compatible with CEE 7/1, CEE 7/3, and CEE 7/5 sockets. It has two round pins measuring 4.8 by 19 mm (0.189 by 0.748 in). The pins are not sheathed, in contrast to e.g. CEE 7/16 Europlugs. It may be rated at either 10 A or 16 A. A typical use is for appliances that exceed the 2.5 A rating of CEE 7/16 Europlugs. It may be used for unearthed Class II appliances (and in South Korea for all domestic non-earthed appliances). It is also defined as the Class II plug in Italian standard CEI 23-50.

It is sometimes called a contour plug, because its collar contour follows that of the socket's recess. The collar prevents accidental contact with the non sheathed pins when inserting or removing the plug in a recessed socket.

It can be inserted into Israeli SI 32 outlets with some difficulty, as well as Danish (type K) ones. The Soviet GOST 7396 standard includes both the CEE 7/17 and the CEE 7/16 variant II plug.

China GB 2099.1-2008 and GB 1002-2008 (Type A & I)

The standard for Chinese plugs and sockets (excluding Hong Kong, Macau and Taiwan) is set out in GB 2099.1-2008 and GB 1002-2008. 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; a slightly larger 16 A version also exists. The nominal pin dimensions of the 10 A version are: 1.5 mm thick by 6.4 mm wide, the line & neutral are 18 mm long, and the earth is 21 mm long. It is similar to the Australian plug. Many 3 pin sockets in China include a physical lockout preventing access to the active and neutral terminals unless an earth pin (which is slightly longer than the other 2 pins) is entered first. China also uses American/Japanese NEMA 1-15 sockets and plugs for Class-II appliances (however, polarized plugs with one prong wider than the other are not accepted); a common socket type that also accepts Europlug (type C) is also defined in GB 1002. The voltage at a Chinese socket of any type is 220 V.

Type I plugs and sockets from different countries have different pin lengths. This means that the uninsulated pins of a Chinese plug may become live while there is still a large enough gap between the faces of the plug and socket to allow a finger to touch the pin.

Danish Section 107-2-D1 earthed (Type K)

This Danish standard plug is described in the Danish Plug Equipment Section 107-2-D1 Standard sheet (SRAF1962/DB 16/87 DN10A-R). The Danish standard provides for sockets to have child-resistant shutters.

The Danish socket will also accept the CEE 7/16 Europlug or CEE 7/17 Schuko-French hybrid plug. CEE 7/4 (Schuko), CEE 7/7 (Schuko-French hybrid), and earthed CEE 7/6 French plugs will also fit into the socket but will not provide an earth connection and may be attached to appliances requiring more than the 13 A maximum rating of the socket.

A variation (standard DK 2-5a) of the Danish plug is for use only on surge protected computer sockets. It fits into the corresponding computer socket and the normal socket, but normal plugs deliberately do not 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, which 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 it is a requirement that the sockets have a cavity to prevent touching the live pins. The shape of the plugs generally makes it difficult to touch the pins when connecting/disconnecting.

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

As of 1 July 2008, wall sockets for French two-pin, female earth CEE 7/5 are permitted for installations in Denmark. This was done because little electrical equipment sold to private users is equipped with a Danish plug. In Europe, devices are usually sold with the Europlug CEE 7/16 and Hybrid plug CEE 7/7, as these fit in most countries. However, in Denmark this often leads to the situation that the protective earth is not connected.

CEE 7/3 sockets were not permitted until 15 November 2011. Many international travel adaptor sets sold outside Denmark match CEE 7/16 (Europlug) and CEE 7/7 (Schuko-French hybrid) plugs which can readily be used in Denmark.

Though Type K remains by far the most common socket in Danish homes as of January 2024, newssites and industry magazines have warned that plugging a Schuko plug directly into a Type K socket can give noticeable electric shocks to the point of pain, be dangerous to the point of hospitalising, or even be life-threatening.

IEC 60906-1 (Type N)

In 1986, the International Electrotechnical Commission published IEC 60906-1, a specification for a plug and socket that look similar, but are not identical, to the Swiss plug and socket. This standard was intended to one day become common 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.

The plug and socket are rated 16 A 250 V AC and are intended for use only on systems having nominal voltages between 200 V and 250 V AC The plug pins are 4.5 mm in diameter, line and neutral are on centres 19 mm apart. The earth pin is offset 3.0 mm. The line pin is on the right when looking at a socket with the earth pin offset up. Shutters over the line and neutral pins are mandatory.

The only country to have officially adopted the standard is South Africa as SANS 164-2.

Brazil developed a plug resembling IEC 60906-1 as the national standard under specification NBR 14136. The NBR 14136 standard has two versions, neither of which has pin dimensions or ratings complying with IEC 60906-1. Use at 127 V is permitted by NBR 14136, which is against the intention of IEC 60906-1.

Israel SI32 (Type H)

The plug defined in SI 32 (IS16A-R) is used only in Israel, the Gaza Strip and the West Bank. There are two versions: an older one with flat pins, and a newer one with round pins.

The pre-1989 system has three flat pins in a Y-shape, with line and neutral 19 mm (0.75 in) apart. The plug is rated at 16 A. In 1989 the standard was revised, with three round 4.5 mm (0.177 in) pins in the same locations designed to allow the socket to accept both older and newer Israeli plugs, and also non-earthed Europlugs (often used in Israel for equipment which does not need to be earthed and does not use more current than the Europlug is rated for). Pre-1989 sockets which accept only old-style plugs have become very rare in Israel.

SI 32 plugs have no sleeve insulation, so when a plug is partially removed its prongs may still be powered although they can be touched by small fingers, metal objects, etc., with a risk of electric shock.

Sockets have a defined polarity; looking at the front, neutral is to the left, earth at the bottom, and line to the right.

Italy (Type L)

Italian plugs and sockets are defined by the standard CEI 23-50 which superseded CEI 23-16. This includes models rated at 10 A and 16 A that differ in contact diameter and spacing (see below for details). Both are symmetrical, allowing the line and neutral contacts to be inserted in either direction. This plug is also commonly used in Chile and Uruguay.

1. 10 A plugs and socket: Pins which are 4 mm in diameter, the centres spaced 19 mm apart. The 10 A three-pin earthed rear entry plug is designated CEI 23-50 S 11 (there are also two side-entry versions, SPA 11 and SPB 11). The 10 A two-pin unearthed plug is designated CEI 23-50 S 10. The 10 A three-pin earthed socket is designated CEI 23-50 P 11, and the 10 A two-pin unearthed socket is designated CEI 23-50 P 10. Both 10 A sockets also accept CEE 7/16 (Europlugs).
2. 16 A plug and socket: Pins which are 5 mm in diameter, the centres spaced 26 mm apart. The 16 A three-pin earthed rear entry plug is designated CEI 23-50 S 17 (there are also two side-entry versions, SPA 17 and SPB 17). The 16 A two-pin unearthed plug is designated CEI 23-50 S 16. The 16 A three-pin earthed socket is designated CEI 23-50 P 17, there is not a 16 A two-pin unearthed socket. The 16 A socket used to be referred to as per la forza motrice (for electromotive force, see above) or sometimes (inappropriately) industriale (industrial) or even calore (heat).

The two standards were initially adopted because up to the second half of the 20th century in many regions of Italy electricity was supplied by means of two separate consumer connections – one for powering illumination and one for other purposes – and these generally operated at different voltages, typically 127 V (a single phase from 220 V three-phase) and 220 V (a single phase from three-phase 380 V or two-phase from 220 V three-phase). The electricity on the two supplies was separately metered, was sold at different tariffs, was taxed differently and was supplied through separate and different sockets. Even though the two electric lines (and respective tariffs) were gradually unified beginning in the 1960s (the official, but purely theoretical, date was the summer of 1974) many houses had dual wiring and two electricity meters for years thereafter; in some zones of Lazio the 127 V network was provided for lighting until 1999. The two gauges for plugs and sockets thus became a de facto standard which is now formalized under CEI 23-50. Some older installations have sockets that are limited to either the 10 A or the 16 A style plug, requiring the use of an adaptor if the other gauge needs to be connected. Numerous cross adaptors were used.

Almost every appliance sold in Italy nowadays is equipped with CEE 7/7 (German/French), CEE 7/16 or CEE 7/17 plugs, but the standard Italian sockets will not accept the first and the third ones since the pins of the CEE 7/7 and CEE 7/17 plugs are thicker (4.8 mm) than the Italian ones (4 mm); besides the pins are not sheathed and forcing them into a linear Italian socket may lead to electric shock. Adaptors are standardized in Italy under CEI 23-57 which can be used to connect CEE 7/7 and CEE 7/17 and plugs to linear CEI 23-50 sockets.

Europlugs are also in common use in Italy; they are standardized under CEI 23-34 S 1 for use with the 10 A socket and can be found fitted to Class II appliances with low current requirement (less than 2.5 A).

The current Italian standards provide for sockets to have child-resistant shutters ("Sicury" patent).

Italian multiple standard sockets

• Old adaptor from forza to 2 × luce and 1 × forza
• CEI 23-50 17/11 (Bipasso) socket (#1) and CEI 23-50 P 40 (Italian adapted Schuko) (#2) in a modern installation
• Italian Vimar universale socket accepting CEE 7/4 (German), CEE 7/7 (German/French), CEE 7/16 (Europlug), CEE 7/17 (German/French unearthed), NEMA 1-15 (US/Japan), CEI 23-50 S 11 (10 A) and S 17 (16 A) Italian plugs
• 4box side socket combining 1 Schuko and 2 CEI 23-50 P 17/11 bipasso (Italian type plugs)

In modern installations in Italy (and in other countries where Type L plugs are used) it is usual to find sockets that can accept more than one standard.

The simplest type, designated CEI 23-50 P 17/11, has a central round hole flanked by two figure-8 shaped holes, allowing the insertion of CEI 23-50 S 10 (Italian 10 A plug unearthed), CEI 23-50 S 11 (Italian 10 A plug earthed), CEI 23-50 S 16 (Italian 16 A plug unearthed), CEI 23-50 S 17 (Italian 16 A plug earthed) and CEE 7/16 (Europlug). The advantage of this socket style is its small, compact face; its drawback is that it accepts neither CEE 7/7 nor CEE 7/17, very commonly found in new appliances sold in Italy. Vimar brand claims to have patented this socket first in 1975 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.

A second, quite common type is called CEI 23-50 P 30 and looks like a Schuko socket, but adds a central earthing hole (optional according to CEI 23-50, but virtually always present). This design can accept CEE 7/4 (German), CEE 7/7 (German/French), CEE 7/16, CEE 7/17 (Konturenstecker, German/French unearthed), CEI 23-50 S 10 and CEI 23-50 S 11 plugs. Its drawback is that it is twice as large as a normal Italian socket, it does not accept 16 A Italian plugs and the price is higher; for those reasons Schuko sockets have been rarely installed in Italy until recent times.

Other types may push compatibility even further. The CEI 23-50 P 40 socket, which is quickly becoming the standard in Italy along with CEI 23-50 P 17/11, accepts CEE 7/4, CEE 7/7, CEE 7/16, CEE 7/17, CEI 23-50 S 10, CEI 23-50 S 11, CEI 23-50 S 16 and CEI 23-50 S 17 plugs; its drawback is that it does not accept SPA 11, SPB 11, SPA 17 and SPB 17 side-entry plugs; however almost no appliance is sold with these types, which are mainly used to replace existing plugs. The Vimar-brand universale (all purpose) socket accepts CEE 7/4, CEE 7/7, CEE 7/16, CEE 7/17, CEI 23-50 S 10, CEI 23-50 S 11, CEI 23-50 S 16, CEI 23-50 S 17 and also NEMA 1-15 (US/Japan) plugs (older versions also had extra holes to accept UK shaver plugs).

North America, Central America and IEC 60906-2

• Left: NEMA 5-15 plug. Right: "Decora"-style duplex socket, with ground-pin up orientation specified in NECA 130-2010, centre. Photos are different scale – parallel blades are on 1⁄2-inch (12.7 mm) centres.
• Ordinary duplex socket mounted in ground-pin down orientation.

Most of North America and Central America, and some of South America, use connectors standardized by the National Electrical Manufacturers Association (NEMA). The devices are named using the format NEMA n-mmX, where n is an identifier for the configuration of pins and blades, mm is the maximum current rating, and X is either P for plug or R for receptacle. For example, NEMA 5-15R is a configuration type 5 receptacle supporting 15 A. Corresponding P and R versions are designed to be mated. Within the series, the arrangement and size of pins will differ, to prevent accidental mating of devices with a higher current draw than the receptacle can support.

NEMA 1-15 ungrounded (Type A)

• NEMA 1-15 polarised plug
• NEMA 1-15 unpolarised plug

NEMA-1 plugs have two parallel blades and are rated 15 A at 125 volts. They provide no ground connection but will fit a grounding NEMA 5-15 receptacle. Early versions were not polarised, but most plugs are polarised today via a wider neutral blade. (Unpolarised AC adaptors are a common exception.)

Harvey Hubbell patented a parallel blade plug in 1913, where the blades were equal width (U.S. patent 1,064,833). In 1916 Hubbell received a patent for a polarised version where one blade was both longer and wider than the other (U.S. patent 1,180,648), in the polarised version of NEMA 1-15, introduced in the 1950s, both blades are the same length, only the width varies.

Ungrounded NEMA-1 outlets are not permitted in new construction in the United States and Canada, but can still be found in older buildings.

NEMA 5-15 grounded (Type B)

The NEMA 5-15 plug has two flat parallel blades like NEMA 1-15, and a ground (earth) pin. It is rated 15 A at 125 volts. The ground pin is longer than the line and neutral blades, such that an inserted plug connects to ground before power. The ground hole is officially D-shaped, although some round holes exist. Both current-carrying blades on grounding plugs are normally narrow, since the ground pin enforces polarity. This socket is recommended in IEC standard 60906-2 for 120-volt 60 Hz installations.

The National Electrical Contractors Association's National Electrical Installation Standards (NECA 130-2010) recommends that sockets be mounted with the ground hole up, such that an object falling on a partially inserted connector contacts the ground pin first. However, the inverted orientation (with ground pin downwards) is more commonly used. The ground-down orientation has been called the "sad socket", "dismayed face", or "shocked face" by some.

Tamper-resistant sockets may be required in new residential construction, with shutters on the power blade sockets to prevent contact by objects inserted into the socket.

In stage lighting, this connector is sometimes known as PBG for Parallel Blade with Ground, Edison or Hubbell, the name of a common manufacturer.

NEMA 5-20

The NEMA 5-20 AP variant has blades perpendicular to each other. The receptacle has a T-slot for the neutral blade which accepts either 15 A parallel-blade plugs or 20 A plugs.

NEMA 14-50

NEMA 14-50 devices are frequently found in RV parks, since they are used for "shore power" connections of larger recreational vehicles. Also, it was formerly common to connect mobile homes to utility power via a 14-50 device. Newer applications include Tesla's Mobile Connector for vehicle charging, which formally recommended the installation of a 14-50 receptacle for home use.

Other NEMA types

30- and 50-amp rated sockets are often used for high-current appliances such as clothes dryers and electric stoves.

JIS C 8303, Class II unearthed

• Japanese Class II polarized sockets with earth post, for a washing machine (similar to NEMA 1-15)
• Japanese 20 A socket with earth post and earth connector, for an air conditioner (similar to NEMA 5-20)
• Japanese 200 V socket with earth slot, for an air conditioner (similar to NEMA 6-20)

The Japanese Class II plug and socket appear physically identical to NEMA 1-15 and also carries 15 A. The relevant Japanese Industrial Standard, JIS C 8303, imposes stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and type approval.

Older Japanese sockets and multi-plug adaptors are unpolarised—the slots in the sockets are the same size—and will accept only unpolarised plugs. Japanese plugs generally fit into most North American sockets without modification, but polarised North American plugs may require adaptors or replacement non-polarised plugs to connect to older Japanese sockets. In Japan the voltage is 100 V, and the frequency is either 50 Hz (Eastern Japan: Tokyo, Yokohama, Tohoku, Kawasaki, Sapporo, Sendai and Hokkaido) or 60 Hz (Western Japan: Osaka, Kyoto, Nagoya, Shikoku, Kyushu and Hiroshima) depending on whether the customer is located on the Osaka or Tokyo grid. Therefore, some North American devices which can be physically plugged into Japanese sockets may not function properly.

JIS C 8303, Class I earthed

Japan also uses a grounded plug similar to the North American NEMA 5-15. However, it is less common than its NEMA 1-15 equivalent. Since 2005, new Japanese homes are required to have class I grounded sockets for connecting domestic appliances. This rule does not apply for sockets not intended to be used for domestic appliances, but it is strongly advised to have class I sockets throughout the home.

Soviet standard GOST 7396 C 1 unearthed

• Soviet grip plug, 6 A 250 V AC, thermoset plastic
• Soviet round plug, 6 A 250 V AC, thermoset plastic, half height
• Moulded rubber Soviet plugs cut with knife so that they can fit into CEE 7/3 socket. Originally the plugs had a round base.
• Soviet shaver power cord. The plug is similar to CEE 7/16, but has different configuration. Thermoplastic plug is rated 6 A and 250 V.

This Soviet plug, still sometimes used in the region, has pin dimensions and spacing equal to the Europlug, but lacks the insulation sleeves. Unlike the Europlug, it is rated 6 A. It has a round body like the European CEE 7/2 or flat body with a round base like CEE 7/17. The round base has no notches. The pins are parallel and do not converge. The body is made of fire-resistant thermoset plastic. The corresponding 6 A socket accepts the Europlug, but not others as the 4.5 mm holes are too small to accept the 4.8 mm pins of CEE 7/4, CEE 7/6 or CEE 7/7 plugs.

There were also moulded rubber plugs available for devices up to 16 A similar to CEE 7/17, but with a round base without any notches. They could be altered to fit a CEE 7/5 or CEE 7/3 socket by cutting notches with a sharp knife.

Swiss SN 441011 (Type J)

The Swiss standard, also used in Liechtenstein and Rwanda (and in other countries alongside other standards) is SN 441011 (until 2019 SN SEV 1011) Plugs and socket-outlets for household and similar purposes. The standard defines a hierarchical system of plugs and sockets with two, three and five pins, and 10 A or 16 A ratings. Sockets will accept plugs with the same or fewer pins and the same or lower ratings. The standard also includes three-phase devices rated at 250 V (phase-to-neutral) / 440 V (phase-to-phase). It does not require the use of child protective shutters. The standard was first described in 1959.

10 A plugs and sockets (Type J)

SEV 1011 defines a "Type 1x" series of 10 A plugs and sockets. The type 11 plug is unearthed, with two 4 mm diameter round pins spaced 19 mm apart. The type 12 plug adds a central 4 mm diameter round earth pin, offset by 5 mm. The type 12 socket has no recess, while the type 13 socket is recessed. Both sockets will accept type 11 and type 12 plugs, and also the 2.5 A Europlug. Earlier type 11 & 12 plugs had line and neutral pins without sleeved pins, which present a shock hazard when partially inserted into non-recessed sockets. The IEC type J designation refers to SEV 1011's type 12 plugs and type 13 sockets.

Unique to Switzerland is a three-phase power socket compatible with single-phase plugs: The type 15 plug has three round pins, of the same dimensions as type 12, plus two smaller flat rectangular pins for two additional power phases. The type 15 socket is recessed, and has five openings (three round and two flat rectangular). It will accept plugs of types 11, 12, 15 and the Europlug.

16 A plugs and sockets

SEV 1011 also defines a "Type 2x" series of 16 A plugs and sockets. These are the same as their 10 A "Type 1x" counterparts, but replace the round pins with 4 mm × 5 mm rectangular pins. The sockets will accept "Type 1x" plugs. The unearthed type 21 plug has two rectangular pins, with centres 19 mm apart. The type 23 plug adds a central rectangular earth pin, offset by 5 mm. The recessed type 23 socket will accept plugs of types 11, 12, 21, 23 and the Europlug.

Again, the three-phase power socket is compatible with single-phase plugs, either of 10 A or 16 A ratings: The type 25 plug has three rectangular pins of the same dimensions as type 23, plus two rectangular pins of the same dimensions as type 15. The corresponding type 25 socket is recessed and will accept plugs of types 11, 12, 15, 21, 23, 25 and the Europlug.

Regulation of adaptors and extensions

A 2012 appendix to SEV 1011:2009, SN SEV 1011:2009/A1:2012 Plugs and socket-outlets for household and similar purposes – A1: Multiway and intermediate adaptors, cord sets, cord extension sets, travel adaptors and fixed adaptors defines the requirements applicable to multiway and intermediate adaptors, cord sets, cord extension sets, and travel and fixed adaptors, it covers the electrical safety and user requirements, including the prohibition of stacking (the connection of one adaptor to another). Non-conforming products must be withdrawn from the Swiss market before the end of 2018.

Pictures

Plug forms from SN 441011 Single-phase, unearthed Single-phase, earthed Three-phase, earthed 2.5 A Europlug 10 A Type 11 Type 12 Type 15 16 A Type 21 Type 23 Type 25

Socket forms from SN 441011 Single-phase, earthed Three-phase, earthed 10 A Type 13 Type 15 16 A Type 23 Type 25

Other Swiss socket forms Type 12 triple socket (10 A), now obsolete and no longer sold or installed Type 14 single socket (10 A), now obsolete Type 13 triple socket (10 A) Type 23 triple socket (16 A)

Thai three-pin plug TIS 166-2549 (Type O)

Thai Industrial Standard (TIS) 166-2547 and its subsequent update TIS 166-2549 replaced prior standards which were based on NEMA 1-15 and 5-15, as Thailand uses 220 V electricity. The plug has two round power pins 4.8 mm in diameter and 19 mm in length, insulated for 10 mm and spaced 19 mm apart, with an earthing pin of the same diameter and 21.4 mm in length, located 11.89 mm from the line connecting the two power pins. The earth pin spacing corresponds to that of NEMA 5 and provides compatibility with prior hybrid three-pin sockets, which accept NEMA 1-15, NEMA 5-15 and Europlugs, all of which have been variably used in Thailand. The hybrid socket is also defined in TIS 166-2547, in addition to a plain three-round-pin socket, with plans to replace the former and phase out support for NEMA-compatible plugs. Sockets are polarised (as in NEMA 5-15).

The plug is similar to, but not interchangeable with, the Israeli SI32 plug. The Thai plug is designated as "Type O" at IEC World Plugs.

Special purpose plugs and sockets

Special purpose sockets may be found in residential, industrial, commercial or institutional buildings. Examples of systems using special purpose sockets include:

• "Clean" (low electrical noise) earth for use with computer systems,
• Device for Connection of Luminaires (DCL) is a European standard for ceiling- and hanging light fixtures.
• Emergency power supply,
• Uninterruptible power supply for critical or life-support equipment,
• Isolated power for medical instruments, tools used in wet conditions, or electric razors,
• "Balanced" or "technical" power used in audio and video production studios,
• Theatrical lighting,
• CEE 17 are a series of industrial grade (IP44) three-phase "pin & sleeve" connectors for industrial purposes, carpentry- and gardening appliances and also used as a weather-resistant connector for outdoor usage, like Caravans, Motorhomes, camper vans and tents for mains hook-up at camp-sites.
• Sockets for electric clothes dryers, electric ovens, and air conditioners with higher current rating.

Special-purpose sockets may be labelled or coloured to identify a reserved use of a system, or may have keys or specially shaped pins to prevent use of unintended equipment.

Single-phase electric stove plugs and sockets

The plugs and sockets used to power electric stoves from a single-phase line have to be rated for greater current values than those used with three-phase supply because all the power has to be transferred through two contacts, not three. If not hardwired to the supply, electric stoves may be connected to the mains with an appropriate high power connector. Some countries do not have wiring regulations for single-phase electric stoves. In Russia, an electric stove can often be seen connected with a 25 or 32 A connector.

In Norway a 25 A grounded connector, rectangular shaped with rounded corners, is used for single-phase stoves. The connector has three rectangular pins in a row, with the grounding pin longer than other two. The corresponding socket is recessed to prevent shocks. The Norwegian standard is NEK 502:2005 – standard sheet X (socket) and sheet XI (plug). They are also known as the two pole and earth variants of CEE 7/10 (socket) and CEE 7/11 (plug).

Shaver supply units

National wiring regulations sometimes prohibit the use of sockets adjacent to water taps, etc. A special socket, with an isolation transformer, may allow electric razors to be used near a sink. Because the isolation transformer is of low rating, such outlets are not suitable to operate higher-powered appliances such as hair dryers.

An IEC standard 61558-2-5, adopted by CENELEC and as a national standard in some countries, describes one type of shaver supply unit. Shaver sockets may accept multiple two-pin plug types including Australian (Type I) and BS 4573. The isolation transformer often includes a 115 V output accepting two-pin US plugs (Type A). Shaver supply units must also be current limited, IEC 61558-2-5 specifies a minimum rating of 20 VA and maximum of 50 VA. Sockets are marked with a shaver symbol, and may also say "shavers only".

Isolation transformers and dedicated NEMA 1-15 shaver receptacles were once standard installation practice in North America, but now a GFCI receptacle is used instead. This provides the full capacity of a standard receptacle but protects the user of a razor or other appliance from leakage current.

Differences between BS4573 Type C and Europlug Type C. The BS4573 plug has round 5mm contacts, spacing 16mm. The Euro-plug has 4mm contacts, spacing 19mm. In order to plug a Europlug into a BS4573 socket, an adaptor is required.

Comparison of standard types

1. ^ Type letters are from the International Electrotechnical Commission (IEC) Web site that provides classification letters similar to a United States Department of Commerce publication that sees widespread but not universal use to differentiate plug and socket types based on rough mechanical compatibility. Most common household plugs have an associated letter.
2. ^ Will accept unearthed plugs.
3. ^ Standard does not define a socket.
4. ^ CEE 7/17 specifies an unearthed hybrid plug that will fit into both the CEE 7/3 and CEE 7/5 sockets.
5. There are some CEE 7/17 plugs with special shape which are polarised when used with CEE 7/5 sockets (mechanically only).
6. CEE 7/1 socket accepts earthed CEE 7/3, CEE 7/5 and CEE 7/7 plugs but provides no earth connection.
7. BS 4573 and BS EN 61558-2-5 do not explicitly specify a current rating for a compliant plug, see BS 4573 section of British and compatible standards.
8. ^ CEE 7/7 specifies an earthed hybrid plug that will fit into both the CEE 7/3 and CEE 7/5 sockets.
9. Plug can only be inserted one way with French CEE 7/5, but lack of wiring convention means that the system is not polarised.
10. ^ The recess provided by CEE 7/3 and CEE 7/5 sockets offers protection against touching the live pins of CEE 7/4, CEE 7/6 and CEE 7/7 plugs. When used in CEE 7/1 (unearthed) sockets, or "universal adaptors" there is no protection for those plugs.
11. Not polarised when used with a CEE 7/3 socket, most CEE 7/7 plugs are (mechanically only) polarised when used with a CEE 7/5 socket
12. The actual rating of non-rewirable plugs is marked according to the fuse fitted by the cord set manufacturer, the fuse rating being determined by the rating of the flexible cable.
13. Except when used with unearthed plugs such as Europlug.
14. Import of plugs with non-partially-insulated pins no longer allowed after 2012.
15. Type L comes in two variations with ratings of 10 A & 16 A having different pin diameters and spacing from each other.

Unusual types

Lampholder plug

• Italian bypass lampholder plugs with Edison screw mount.
  Left: early type (porcelain and brass, c. 1930).
  Right: late type (black plastic, c. 1970)
• Lampholder plug (US, c. 1950–1960)

A lampholder plug fits into a light socket in place of a light bulb to connect appliances to lighting circuits. Where a lower rate was applied to electric power used for lighting circuits, lampholder plugs enabled the consumers to reduce their electricity costs. Lampholder plugs are rarely fused. Edison screw lampholder adaptors (for NEMA 1-15 plugs) are still commonly used in the Americas.

Soviet adaptor plugs

Some appliances sold in the Soviet Union had a flat unearthed plug with an additional pass-through socket on the top, allowing a stacked arrangement of plugs. The usual Soviet apartment of the 1960s had very few sockets, so this design was very useful, but somewhat unsafe; the brass cylinders of the secondary socket were uncovered at the ends (to allow them to be unscrewed easily), recessed by only 3 mm, and provided bad contact because they relied on the secondary plug's bisected expanding pins. The pins of the secondary plug (which lacked insulation sleeves) could not be inserted into the cylindrical sockets completely, leaving a 5 mm gap between the primary and secondary plugs. The adaptors were mostly used for low power appliances (for example, connecting both a table lamp and a radio to a socket).

UK Walsall Gauge plug

Unlike the standard BS 1363 plugs found in the UK, 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 university laboratories (from batteries) and the BBC, and is still in use in parts of the London Underground for 110 V AC voltage supply. In the 1960s they were used for 240 V DC in the Power laboratory of the Electrical Engineering department of what was then University College, Cardiff. Power was supplied by the public 240 V DC mains which remained available in addition to the 240 V AC mains until circa 1969, and thereafter from in-house rectifiers. They were also used in the Ministry of Defence Main Building inside circuits powered from the standby generators to stop staff from plugging in unauthorised devices. They were also known to be used in some British Rail offices for the same reason.

Italian BTicino brand Magic Security connector

• Magic Security socket, detail.
• Assortment of Magic Security sockets (in orange, the industrial three-phase type)
• Assortment of Magic Security plugs
• Magic Security plug (10 A) (left) with a type L to Magic Security plug adaptor

In the 1960s, the Italian firm BTicino introduced an alternative to the Europlug or CEI 23-16 connectors then in use, called Magic Security. The socket is rectangular, with lateral key pins and indentations to maintain polarisation, and to prevent insertion of a plug with different current ratings. Three single-phase general purpose connectors were rated 10 A, 16 A and 20 A; and a three-phase industrial connector rated 10 A; all of them have different key-pin positioning so plugs and sockets cannot be mismatched. 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 positioned on both sides of the plug; the plug is energised only when it is inserted fully into the socket.

The system is not compatible with Italian CEI plugs, nor with Europlugs. Appliances were never sold fitted with these security plugs, and the use of adaptors would defeat the safety features, so the supplied plugs had to be cut off and replaced with the security connector. Even so, the Magic security system had some success at first because its enhanced safety features appealed to customers; standard connectors of the day were not considered safe enough. The decline of the system occurred when safety lids similar to the Magic type were developed for standard sockets.

In Italy, the system was never definitively abandoned. Though very rarely seen today, it is still marked as available in BTicino's catalogue, (except for the three-phase version, which stopped being produced in July 2011).

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 plugs 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.

See also

• Anderson Powerpole
• DC connector
• History of AC power plugs and sockets
• IEC 60309 high-power industrial and polyphase connectors
• IEC 60320 Appliance couplers for household and similar general purposes
• Industrial and multiphase power plugs and sockets
• Mains electricity
• Mains electricity by country lists voltage, frequency, and connector types for over 200 countries
• Perilex
• Pattress
• Plug load
• Polyphase system
• Smart plug
• Stage pin connector
• Light switch

References

1. John Mellanby (1957). The History of Electric Wiring. London: Macdonald.
2. "Universal AC Outlet • Setup Guide" (PDF). Anaheim, CA: Extron Electronics. November 2017. 68-1638-01 Rev. F. Archived from the original (PDF) on 16 May 2018. Retrieved 21 May 2018.
3. "Alert noting non-compliant power strips" (PDF). 2009. Archived from the original (PDF) on 6 March 2016. Retrieved 25 October 2019.
4. "Sri Lanka Sets National Standard for Plugs and Socket Outlets". Public Utilities Commission of Sri Lanka. Archived from the original on 2 April 2019. Retrieved 25 October 2019. Standardized on Type G; sale of non-compliant sockets is banned as of August, 2018, and buildings must re-wire by August, 2038.
5. James S. Jennings. "Army Sustainment: The Three Most Common Electrical Safety Issues in Deployed Environments". Archived from the original on 23 February 2015.
6. "Universal Sockets Are Unsafe". Interpower Corporation. Interpower. Retrieved 6 July 2018.
7. ^ World Plugs Retrieved on 27 March 2015.
8. ^ The letter system first appeared in such guides in 1967 (Electric Current Abroad. United States Department of Commerce, 1967. Retrieved on 14 December 2013.) which designated types A two-pin US, B (BS 546), and C (BS 1363). The 1984 edition (Electric Current Abroad. United States Department of Commerce, 1984. Retrieved on 14 December 2013.) uses the letters A to G in the same manner as they are used today, and the last revision of the print series was in 1998 ("Electric Current Abroad" (PDF). US Department of Commerce, International Trade Administration (retrieved 9 October 2015). 2002.). The International Trade Administration of the US Department of Commerce now publishes a web version: Electric Current Worldwide, which differs slightly from the IEC list and from Misplaced Pages's list at Mains electricity by country.
9. ftp://ftp.cencenelec.eu/CENELEC/TCs/61/PlugsSockets.pdf Plugs and socket types in each CENELEC country, Retrieved 15 February 2012.
10. AS/NZS 3112:2004, Approval and test specification – Plugs and socket-outlets, Standards Australia and Standards New Zealand
11. "Mains Plugs with Insulated Pins. Australian Standards AS/NZS3112:2000 & AS/NZS3112:2004 refer [sic]". Access Communications. 19 April 2007.
12. ^ NBR 14136:2002 – Plugues e tomadas para uso doméstico e análogo – Padronização [Plugs and socket-outlets for household use and similar purposes – Specification] (in Portuguese), BR: ABNT, 2002
13. "Norma ABNT NBR 14136:2002" (in Portuguese). BR: Projeto de redes.
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External links

• Digital Museum of Plugs and Sockets (comprehensive collection of plugs and sockets)
• Glossary of standards terms
• Edison thread

• Electrical standards
• Electrical wiring
• Mains power connectors