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 receptacles for two power pins, one to carry the electrical current from the power source to the connected device (called live, line, or phase pin) and another one to carry it back to the power source (called neutral pin). Many sockets have a third receptacle or pin for a safety connection to earth ground. The plug is a male connector, usually with protruding pins that match the receptacles (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, hence the power pins are always part of the plug rather than 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. One of the first national standards for plugs and wall sockets was enacted in 1915 in the UK.
Safety features
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, particularly the British Type G, have a built-in fuse which breaks the circuit if too much current flows.
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.
<span class="anchor" id="Polarisation"></span>Polarization
Where a "neutral" conductor exists in supply wiring, polarization of the plug can improve safety by preserving the distinction in the equipment. For example, appliances may ensure that switches interrupt the live side of the circuit, or can connect the shell of a screw-base lampholder to neutral to reduce electric shock hazard. In some designs, polarized plugs cannot be mated with non-polarized sockets. In most 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 polarized plugs.
Voltage rating of plugs and power cords
thumb|Ratings of NEMA 5-15 (Type B) plug marked on the label (left: 7 A 125 V), engagement face, and [[IEC 60320 C13 connector at the appliance end of the cord (centre, right: both 10 A 125 V)]]
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
thumb|A plug strip with two USB ports and built-in [[Surge protector|surge protection]]
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
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 for 6 A, 10 A, or 16 A at 250 V or for 15 A or less at 125 V. This is the general rating of the adaptor, and indicates the maximum total load in amperes, 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 such 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
Hybrid and universal sockets
"Hybrid", "multi-standard", or "universal" sockets are intended to accommodate plugs of two or more 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 that accepts A and C plugs and an earthed socket that accepts Type I plugs. Since the 2021 revision of the Chinese standard, the installation of such dual sockets is no longer allowed in China, but they can still be found in many existing installations.
Such Thai or Chinese dual sockets also 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 countries supply residential power at 220–230 V. These dual sockets also accept French and Schuko plugs (Types E and F), but unsafely: no earth contact is established and live pins may be exposed when a plug is partially inserted. 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.
Australasian AS/NZS 3112 and compatible plugs (Type I)<span class="anchor" id="Type I"></span>
A number of countries in Oceania as well as China and Argentina use a plug that has two flat pins at an angle, forming a V-shape, as well as a flat vertical grounding pin. While the exact pin dimensions and the polarity vary between different countries, these plugs and sockets are all compatible to each other and are known as Type I.
Argentina IRAM 2073 and 2071
thumb|Type I grounded plug and socket, both rated for 10 A. Insulating sleeves around the power pins are optional in Argentina and in this case missing. The socket is installed with the earth receptacle down, as usual in Argentina.
The plug and socket system used in Argentina is defined by several standards of the Argentine Normalization and Certification Institute (IRAM). IRAM 2071 defines two sockets that have the same form factor, but differ in size and rating. The smaller, more common socket is rated for 10 A. The larger variant, rated for 20 A, is mostly used for higher-power appliances such as air conditioners. IRAM 2073 defines the corresponding plugs used for Class I appliances (that require earthing). The plug and socket system has an earthing pin and two flat current-carrying pins forming an inverted V-shape (120°).
The pins for the 10 A version measure . The power pins are set at 30° to the vertical with a distance of from their centres to the centre of the plug; they are long. The earthing pin is long and placed below the plug centre at a distance of . The pins of the 20 A version are larger – – and placed further away from the centre of the plug – for the power pins, for the earthing pin. At , the earthing pin is a bit longer, while the power pins are a bit shorter at .
There is also an unearthed version of the 10A plug, defined by IRAM 2063, that lacks an earthing pin and can be used with Class II appliances. 20A plugs, on the other hand, must always provide earthing.
Insulating sleeves around the upper parts of the power pins are allowed, but not required. When used, they significantly reduce the risk of electric shock from accidentally touching the pins of a partially inserted plug. Because the pins of the 20 A plug are placed farther apart than those of the 10 A plug, the two Argentine plug types are mutually incompatible. It is not possible to insert a 20 A plug into a 10 A socket or vice versa. In Argentina, when the earth contact is positioned downward, the live (line) contact is on the right side of the socket, while in Australasia and China it is on the left (assuming the same orientation).
In Brazil, Type I–style plugs and sockets are still commonly used in old installations for high-power appliances like air conditioners, dishwashers, and household ovens. These are often called "Argentine plugs" and are indeed physically identical to the IRAM plugs rated for 20 A, though they might have been developed independently on the basis of the American NEMA 10-20 standard (which uses the same form factor). While these plugs are sometimes used for normal single-phase power and wired in the same way as in Argentina, some are wired for split-phase power with two "hot" (or phase) wires and a neutral wire, but no earth connection. Care must therefore be taken that the same wiring scheme is used in the socket and in the plug, since otherwise the equipment would surely be damaged. In newer installations, the 20 A version of the Type N plug, adopted by Brazil as national standard NBR 14136, is generally preferred.
Australian/New Zealand standard AS/NZS 3112
10 A, 15 A, 20 A, 25 A, and 32 A single-phase sockets. Each socket accepts plugs of equal or lesser current rating.|thumb|upright=0.5
This Australian/New Zealand standard is used in Australia, New Zealand, Fiji, Tonga, Solomon Islands, and Papua New Guinea. The plug shape and basic dimensions are identical to the 10 A plug used in Argentina. The Australasian standard defines a series of plugs and sockets for devices drawing up to 10, 15, 20, 25 and 32 A that are one-way compatible.
In the 15 A plug, the height of the earth pin is increased from 6.35 to , while the dimensions of the power pins remain the same. In the 20 A plug, however, their height is increased in the same way, so that the surface dimensions of the three pins are again identical. The current version is AS/NZS 3112:2025.
<span class="anchor" id="China GB 2099.1"></span>China GB 2099.1 and GB 1002 (Type A & I)
thumb|upright=0.9|Chinese three-pin socket and compound socket which also accepts NEMA and Europlug (right), and a less common, larger 16 A version (left)
The standard for Mainland Chinese plugs and sockets (excluding Hong Kong and Macau) is set out in GB 2099.1 and GB 1002. 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 plugs are three-wire, earthed, rated for 10 or 16 A, 250 V, and are chiefly used for Class I applications. The pins of the 10 A version are thick by wide; the centres of the power pins are placed from the plug centre, while the centre of the earth pin is away. In both plug types, the live and neutral pins are long, while the earth pin is long. This makes the 10 A version compatible with Argentine and Australasian 10 A sockets, as their dimensions are nearly identical. This makes this plug compatible with the 20 A sockets used in Argentina. It is, however, incompatible with Chinese 10 A sockets as well as all Australasian sockets because of the different pin spacing.
Some 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 two pins) is entered first; others require pins to be inserted into both live terminals to open the shutter. Since its 2024 revision, GB 1002 also defines unearthed two-pin Class II plugs, though such plugs cannot be inserted into sockets that require an earth pin to open the shutters. Already since 2008 for 16 A, there is an unearthed Class II plug variant that uses an unwired dummy earth pin to open the shutters; unearthed plugs of this kind fit into all Chinese sockets of the same rating.
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). Older versions of GB 1002 also defined a socket type that accepts Europlugs (Type C), but this hybrid socket was removed from the 2021 revision of the standard. they will be mandatory from 2027.
BS 546 and related types (Type D and M)<span class="anchor" id="Type D"></span><span class="anchor" id="Type M"></span>
thumb|BS 546 plugs. Left to right: 15 A, 5 A and 2 A.
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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 polarized 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 (among them India) and about 15 countries use Type M.
BS 1363 (Type G)
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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 Ireland, Cyprus, Macau, Malaysia, Malta, Saudi Arabia, Singapore, Brunei, Sri Lanka, and the 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 (British shaver)
thumb|right|upright=0.4|BS 4573 plug
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The United Kingdom, Ireland, and Malta use the BS 4573 two-pin plug and socket for electric shavers and toothbrushes. The plug has insulating 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
thumb|upright=1.15|The CEE 7/7 plug is the shape-based intersection of two previously incompatible connectors. It made it possible to largely unify the European market without replacing a single socket, because it no longer matters whether the sockets provide grounding clips (CEE 7/3) or a grounding pin (CEE 7/5).
The CEE 7 standard is a set of general specifications and standard sheets for AC plugs and sockets, first created by the IECEE standards body in 1951. They are now the main system in use in most of Europe. CEE 7 incorporates the two round pinned (with centres spaced at 19 mm) Schuko or Type F plug that was patented by Siemens-Schuckertwerke in 1929, and also the Type E plug, likely developed in Belgium around 1930 but never patented, therefore adopted by Czecho­slovakia, Poland and France. CEE 7 have also developed and incorporated "universal" plugs that will work on both Type E and Type F sockets such as the Europlug.
European countries (whether EU or non-EU) 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. The CEE 7 system has been adapted in many countries outside of Europe as well.
CEE 7/1 unearthed socket and CEE 7/2 unearthed plug
thumb|upright=0.6|CEE 7/1 wall socket, accepts CEE 7/2 (unearthed) plugs and (unsafely) also CEE 7/4, CEE 7/6 and CEE 7/7 (earthed) plugs.
CEE 7/1 sockets and CEE 7/2 plugs are 2-pole connectors rated 10/16 A up to 250 V, with pins. It has no protective earth and therefore poses a risk of electric shock due to missing circular recess. Their sale or use has been banned in a number of countries.
CEE 7/3 socket and CEE 7/4 plug (German "Schuko"; Type F)<span class="anchor" id="Type F"></span>
thumb|Schuko plug (CEE 7/4) and socket (CEE 7/3)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). It is rated at 16 A. 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 . The Schuko system is unpolarized, allowing live and neutral to be reversed.
The plug is used in most European countries and on other continents, including in South Korea and Uruguay.
The plug is rated at 16 A and looks similar to CEE 7/4 plugs, but with earth contacts to fit both CEE 7/5 and CEE 7/3 sockets. Due to its compatibility with the inherently unpolarized Schuko (CEE 7/4) plugs, appliances using it cannot expect the current to flow in any particular direction.
CEE 7/16 Alternative I
The CEE 7/16 Alternative I unearthed plug is used for unearthed appliances. It has two round pins, rated at 2.5 A. 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)<span class="anchor" id="Type C"></span><span class="anchor" id="Europlug"></span>
thumb|upright=.9|Europlug
Alternative II, popularly known as the Europlug, is a flat 2.5 A-rated plug with two round pins, 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 live and neutral are connected arbitrarily. To improve contact with socket parts the Europlug has slightly flexible pins which converge toward their free ends.
The Europlug is widely used in most of Europe and parts of the Middle East, Africa, South America, and Asia. There is no socket defined to accept only the Europlug. Instead, it fits a range of sockets including all three CEE 7 sockets (unearthed, German/"Schuko", and Belgian/French) and also many non-CEE 7 standard sockets such as Swiss, Danish and Italian (10 A) ones as well as Israeli sockets. British shaver sockets also accept Europlugs, although in this configuration the connection supply is only rated at 200 mA.
CEE 7/17 unearthed "contour" plug
thumb|upright=.75|Hybrid unearthed CEE 7/17 plug
This is a round plug compatible with all three types of CEE 7 sockets. Also called the "contour plug", it has two round pins measuring . 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.
Danish plug (Type K)
thumb|Standard Danish plug and socket
This Danish standard plug is described in the Danish Plug Equipment Section 107-2-D1 Standard sheet (SRAF1962/DB 16/87 DN10A-R). Like in most European plugs, the power pins of Danish plugs are long and spaced apart, with a diameter of . The earthing pin is part of the plug (in contrast to French and Schuko plugs); it is D-shaped, long, and offset from the power pins by . It is thick with a diameter of . Sockets and plugs are rated for 16A. The Danish standard provides for sockets to have child-resistant shutters. Sockets are polarized in the same way as British ones: if earth is at the bottom, live is at the left of the socket.
Europlugs (CEE 7/16) and contour plugs (CEE 7/17) can safely be used with Danish sockets. Physically the sockets also accept earthed CEE 7/4 (Schuko), CEE 7/6 (French), and CEE 7/7 (Schuko-French hybrid) plugs, but no earth connection will be established. Therefore news sites and industry magazines warn that plugging these directly into a Type K socket can give noticeable electric shocks, be dangerous and even be life-threatening.
thumb|Two sockets for the tilted flattened pins and half-round earth pin of a Danish computer plug. On the right is a normal socket (which can also accept computer plugs).
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 they must be recessed to prevent touching the live pins. 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 by 1 July 2008.
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 another variation for hospital equipment with a rectangular left pin, which is used for life support equipment.
IEC 60906-1 (Type N)
thumb|IEC 60906-1 (Type N) socket|upright=0.9
thumb|Three-pin 16 A plug conforming to South African Standard SANS 164-2|upright=0.9
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, live and neutral are on centres 19 mm apart. The earth pin is offset by 3.0 mm. The live pin is on the right when looking at a socket with the earth pin offset up. Shutters over the live and neutral pins are mandatory.
The first country to have officially adopted the standard is South Africa (as SANS 164-2). Paraguay has also adopted it as national standard (PNA-IEC 60906-1), but so far its application is voluntary, and , there is no indication that sockets of this type are commonly installed in the country.
Brazil developed a plug resembling IEC 60906-1 as the national standard under specification NBR 14136. 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.
Due to their smaller pin diameter, Brazilian plugs rated for 10A also fit into Brazilian sockets rated for 20A and South African sockets rated for 16A. 20A plugs do not fit into 10A sockets, which is as intended. However, if the Brazilian and South African variants are mixed, due to receptacle tolerances it might be possible to insert a 16A plug into a 10A socket or a 20A plug into a 16A socket, which could overload the socket.
Israel SI32 (Type H)
thumb|upright=.9|Two Israeli plugs and one socket. The left plug is the old standard; the one on the right is the 1989 revision.
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 live and neutral apart. The plug is rated at 16 A. In 1989 the standard was revised, with three round pins in the same locations designed to allow the socket to accept both older and newer Israeli plugs, and also non-grounded Europlugs (often used in Israel for equipment which does not need to be grounded and does not use more current than the Europlug is rated for).
Italy (Type L)
Italian plugs and sockets are defined by the standard CEI 23-50 and referred to as "Type L". This includes models rated at 10 A and 16 A that differ in contact diameter and spacing. Both are symmetrical, allowing the live and neutral contacts to be inserted in either direction. The 10 A plug has 4 mm diameter pins and the centres spaced 19 mm apart, while the 16 A plug has 5 mm diameter pins and the centres spaced 26 mm apart. This plug type is also used in Chile and Uruguay.
The two form factors 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).
thumb|A CEI 23-50 P40 socket (Italian adapted Schuko) next to a CEI 23-50 P17/11 (bipasso) socket in a modern installation
Modern installations in Italy (and in other countries where Type L plugs are used) typically use sockets that accept several plug types. The simplest type, designated CEI 23-50 P17/11, has a central round hole flanked by two figure-8 shaped holes, allowing the insertion of Italian 10 A and 16 A plugs as well as Europlugs. These compact hybrid sockets are known as presa bipasso (twin-gauge socket). A larger, but more flexible hybrid socket is called CEI 23-50 P40. It merges the bipasso form factor with a "Schuko" socket, thus also accepting earthed CEE 7/4 (Schuko) and CEE 7/7 (CEE hybrid) as well as unearthed CEE 7/17 ("contour") plugs.
Many appliances sold in Italy today are equipped with hybrid CEE 7/7 or CEE 7/17 plugs, but only these larger CEI 23-50 P40 sockets will accept them without an adapter. However, adaptors that allow plugging them into smaller sockets are also commonly sold and regulated by a specific standard.
North America, Central America and IEC 60906-2<span class="anchor" id="NEMA"></span>
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) <span class="anchor" id="Type A"></span>
NEMA 1-15 polarized plug|thumb|upright=0.9
NEMA 1-15 unpolarized plug|thumb|upright=0.9
NEMA-1 plugs have two parallel blades and are rated 15 A at 125 volts. They provide no ground connection but will fit into a grounding NEMA 5-15 receptacle. Early versions were not polarized, but today most plugs are polarized via a wider neutral blade. (Unpolarized AC adaptors are a common exception.) Harvey Hubbell patented a parallel blade plug in 1913, where the blades were equal width (). In 1916 Hubbell received a patent for a polarized version where one blade was both longer and wider than the other (). In the polarized version of NEMA 1-15, introduced in the 1950s, both blades are the same length, with only the width varying.
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) <span class="anchor" id="Type B"></span>
thumb|upright=0.9|Ungrounded vs grounded NEMA plugs
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 live 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 and many plugs have round ground pins. Both current-carrying blades on grounding plugs may be narrow, since the ground pin enforces polarity, but outlets have a wider opening for the neutral blade to prevent ungrounded polarized plugs from being put in backwards. This socket is recommended in IEC standard 60906-2 for 120-volt 60 Hz installations.
The National Electrical Contractors Association's installation standard (NEIS 130-2016) requires a consistent orientation for sockets installed together or nearby, but does not prescribe any specific orientation.
In practice, most sockets are mounted with the ground contact below the other contacts. This ground-down orientation has been called the "sad socket", "dismayed face", or "shocked face" – names which reflect pareidolia.
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
thumb|upright=0.6|5-20RA (Canada) or 5-20R (US) T-slot socket mounted with the earth hole up. The neutral connection is the wider T-shaped slot on the right.
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
left|thumb|upright=0.75|NEMA 14-50 outlet
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
240 V 20-, 30- and 50-amp rated sockets are often used for high-current appliances such as air conditioners, clothes dryers and electric stoves, respectively.
JIS C 8303, Class II unearthed<span class="anchor" id="Japan"></span>
The Japanese Class II plug and socket appear physically identical to NEMA 1-15 and also carries 15 A. The relevant Japanese Industrial Standards, 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 unpolarized—the slots in the sockets are the same size—and will accept only unpolarized plugs. Japanese plugs generally fit into most North American sockets without modification, but polarized North American plugs may require adaptors or replacement non-polarized 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<span class="anchor" id="Japan earthed"></span>
Japan also uses a grounded plug similar to the North American NEMA 5-15.
Swiss SN 441011 (Type J)
thumb|Type J: The 10 ampere SN 441011 type 13 socket (here: a triple socket) and type 12 plug
The Swiss standard, also used in Liechtenstein, 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 does not require the use of child protective shutters.
10 A plugs and sockets (Type J)
SN 441011 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 obsolete type 12 socket had no recess, while the newer 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 and 12 plugs had live 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. replaced prior standards which were based on NEMA 1-15 and 5-15, as Thailand uses 230 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 standard also defines an ungrounded plug with a smaller form factor that is very similar to the Europlug (but a bit higher); its power pins are identical to the grounded variant and both are rated for up to 16 A (while the Europlug is only rated for 2.5 A). The generally used hybrid socket is also defined in TIS 166-2547, in addition to a plain three-round-pin socket, with plans to eventually replace the former and phase out support for NEMA-compatible plugs. Sockets are polarized (as in NEMA 5-15).
The grounded 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
thumb|upright|400 V CEE sockets with cables plugged in.
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, campervans 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
thumb|Plug (sheet V) and socket (sheet VI) to French standard NF C 61-315 (400 V, 32 A)
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, 32, or even 40 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).
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.
Though BS 4573 plugs look similar to Europlugs (Type C), there are subtle differences between them. While the BS 4573 plug has round 5 mm contacts, spaced at 16 mm, the Europlug has 4 mm contacts, spaced at (roughly) 19 mm. In order to insert a Europlug into a BS 4573 socket, an adaptor should be used.
Comparison of standard types
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! IEC<br />TR<br />60083<br />World<br />Plugs<br />Type