AC power plugs and sockets

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.

Different types of plug are used for different IEC appliance classes. The assigned class depends on whether the device is earthed and the degree of insulation it incorporates. Class I, for example, refers to earthed equipment that requires a third contact in the plug and socket, while Class II refers to unearthed equipment protected by double insulation.

Polarization

Where the building wiring system defines a "neutral" conductor that is close to earth potential, it is an advantage for appliance designers to preserve that distinction. For example, appliances may ensure that single-pole switches interrupt the line side of the circuit, or ensure that screw-base lampholder shells are connected to the neutral side of the supply, minimizing the chance of contact with live parts. This requires a plug that can be connected to the socket in only one way, so that the energised and neutral conductors are not interchanged. In most designs, such "polarized" plugs cannot be mated with non-polarized sockets. Wiring systems where both circuit conductors have a significant potential with respect to earth do not benefit from polarized plugs.

Polarization is maintained by the shape, size, or position of plug pins, socket apertures, and socket recesses to ensure that a plug fits only one way into a socket. Lamps with screw bases connect the shell of the lamp socket to the neutral conductor. Similarly, the single-pole switch of the appliance is connected in series with the energized wire. However, because of the uncertainty, in practice, of which conductor is the neutral, some appliances have dual-pole switches, which interrupt both conductors.

Though rotationally asymmetrical, Argentinean connectors have the opposite polarity to those of other Type I countries.

Universal sockets and adapters

"Universal" or "multi-standard" sockets are intended to accommodate plugs of various types and standards. They are sometimes used in China^[14] and other Asian countries, such as India,^[15] Indonesia,^[16] Japan,^[17] Singapore,^[18] Taiwan,^[19] and the Philippines.^[20] In some countries, and other jurisdictions, they violate electrical (safety) standards that apply to portable sockets (such as power strips) or fixed sockets (wall outlets). This includes Singapore,^[21] Sri Lanka,^[22] the European Union, and Switzerland.^[23]

Safety advocates, the United States Army,^[24] and Interpower corporation^[25] point out a number of safety issues, including the following:

• They can allow plugging of 120 V equipment into 230 V mains, potentially resulting in equipment damage. To avoid this, users must know the voltage requirements of their appliances, as well as the local voltage of the socket they are using.^[26]
• It is possible, in some cases, to mis-insert plugs. For example, when a line wire is connected to earth.^[26]
• Some appliances require earthing, but universal sockets often omit the earthing connection for certain plugs. For example, universal sockets with flat engagement surfaces fail to provide an earthing contact for Type F (CEE 7/4 "Schuko"), Type E (CEE 7/6 French), and combination E/F (CEE 7/7) plugs.^[27]
• Some universal sockets allow appliances to be connected to an electricity supply with the appliance requiring a higher current than what the circuit is designed for.
• In some cases, users are not protected from contact with live electrical leads in exposed sockets or half-inserted plugs.^[26]
• Sometimes plugs can be inserted with the wrong polarization between line and neutral. In that case, the power switch on the appliance may leave internal circuitry energized when it should be at earth voltage. This happens in sockets where the two line/neutral holes for NEMA plugs are the same size,^[28] and in outlets designed to accept both NEMA and BS 1363 plugs, where the polarization can only be correct for one type of plug.^[29][30]
• Some universal sockets lack adequate fuse protection. In the United Kingdom, most sockets are connected to a ring final circuit (capable of supplying 32 A) rather than a radial. Adequate protection for the flexible cord is provided by the fuse in the BS 1363 plug. If a universal socket is connected to a ring final circuit and anything other than a BS 1363 plug is inserted into it, then there is a risk of fire in case of a fault condition.^[26]
• The electrical contact made with some universal sockets is poor, which can result in arcs and overheating of the metal parts that do make contact.^[26]
• With some universal sockets the mechanical contact is poor, meaning plugs can easily fall out.^[26]
• Some universal sockets, designed to accept British plugs, have pin apertures that are larger than allowed by BS 1363, and are therefore not legal for British or Irish use.^[31]
• The Low Voltage Directive of the European Union specifically excludes domestic plugs and sockets^[32] and CE marking is neither applicable nor permitted on plugs and sockets. However, CE marking is sometimes fraudulently used on universal sockets.^[33]

These criticisms should not be taken to apply to sockets such as Thai and Chinese dual sockets. The Thai dual socket is specified in figure 4 of TIS 166-2549 (shown below) 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. The exception is that both Thai and Chinese dual sockets also accept 120 V rated plugs, potentially causing an electrical incompatibility because both states use a 220 V residential voltage.

• 
  A so-called 'universal socket', which meets no standard^[34] 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 electrically incompatible with US devices.
• 
  Chinese dual socket accepting both unearthed 2-pin (upper) and earthed 3-pin (lower) plugs.

Voltage rating of plugs and power cords

NEMA 5-15 (type B) plugs with current and voltage ratings shown (left) on label (7 A 125 V) and (centre) on engagement face (10 A 125 V). Also shown (right) is the rating on the C13 connector at the other end of the 10 A 125 V appliance cord.

Plugs and power cords have a rated voltage (V) and rated current (A) assigned to them by the manufacturer, and these values are required by IEC 60884-1 (which might not be legally binding in a given country) to be marked on the plug.^[35] Using an appliance, 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.

Appliance connections and extensions

So that manufacturers need not build, distribute and maintain many similar appliances differing only in the type of plug fitted, a common strategy is to provide an IEC 60320 inlet on the appliance and a detachable power cord (mains flex lead) to allow connection of the appliance to the socket. The appliance need only to be tested to the power inlet. Some types of appliance require the consumer to also change a switch to adapt to different voltages or frequency. In addition to sockets permanently attached to building wiring, extension cords (extension leads) are used for temporary connections when a socket is not within convenient reach of an appliance's power lead. A power strip can also include switching, surge voltage and over-current protection.

Adapters and converters

Plugs and sockets are usually designed as a system to meet standards for safety and reliability. Occasionally, plug and socket combinations may allow power to flow but may not meet product standards for mating force, earthing, current capacity, life expectancy, or safety. Failure to meet quality standards is even more likely when using third-party adapters or improvised user-modified connectors. Physical compatibility does not always ensure that the appliance and socket match in frequency or voltage. Retailers generally distinguish between travel adapters which transform physical connection but not voltage, converters which transform physical connection and voltage. Mismatch in frequency between supply and appliances may still cause problems even at the correct voltage.

Differences in pin length

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.

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,
• Electric car charging, IEC 62196, SAE J1772, Type 2 connector,
• 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,
• 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.

Shaver supply units

Shaver supply unit for BS 4573, US Type A, Australian two-pin, and Europlug Type C.

National wiring regulations sometimes prohibit the use of sockets within certain areas adjacent to water taps, etc. In such cases shaver supply units meeting IEC 61558-2-5 may be permissible. This has been adopted as a European CENELEC standard EN 61558-2-5 and also as a national standard in some countries, e.g. UK (BS EN 61558-2-5) and Malaysia (MS IEC 61558-2-5).

For such shaver supply units, an isolation transformer is required, and sockets usually accept multiple two-pin plug types including Europlug (Type C), 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.^[36] IEC 61558-2-5 requires sockets to be marked with the shaver symbol defined in IEC 60417-5225, the words "shavers only" are also often used but not required.

Argentina IRAM 2073 and 2071 and compatible types (Type I)

The plug and socket used in Class 1 applications in Argentina is defined by IRAM. The applicable 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." It is similar in appearance to the Australasian and Chinese plugs. It has an earthing pin and two flat current-carrying pins forming an upside down 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. The poles plugs 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 Argentinian plug is wired with the line and neutral contacts reversed.

Argentinian 1996 power plug arrangement

In Brazil, similar plugs and sockets are still commonly used for high-power appliances like air conditioners, dishwashers, and household ovens. Although being often called "Argentinian plug," it is actually based on the American NEMA 10-20 standard, and is incompatible with Argentinian 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.

Australasian standard AS/NZS 3112 (Type I)

Australian 2005 standard power plug with insulated pins

Australasian switched 3-pin dual power point (socket) rated 10 amperes

The plug used in Australia, New Zealand, Fiji, Tonga, Solomon Islands, and Papua New Guinea has an earthing pin and two flat current-carrying pins forming an upside down V-shape.^[43] 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 almost always have switches on them for extra safety, as in the UK. An unearthed version of this plug with two angled power pins but no earthing pin is used with small double-insulated appliances, but the 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 of a lower current capacity, but not of higher capacity. For example, a 10 A plug will fit all sockets but a 20 A plug will fit only 20, 25 and 32 A sockets. In New Zealand PDL 940 "Tap-on" or Piggy-back plugs are available which allow a second 10 A plug, or a charger, to be fitted to the rear of the plug.

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 superseded by AS 3112 in 1990. The requirement for insulated pins was introduced in the 2004 revision.^[44] The current version is AS/NZS 3112:2011, Approval and test specification – Plugs and socket-outlets.

Brazilian standard NBR 14136 (Type N)

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).^[45] 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.^[46] 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 didn't connect it. The new standard has an earth pin, which in theory eliminates the need for the flying earth tail.^[47]

Brazilian 10 ampere socket and plugs 

Brazilian 20 ampere socket 

British and compatible standards

BS 546 and related types (Type D and M)

BS 546 plugs. Left to right: 15 A, 5 A and 2 A.

BS 546, "Two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors for AC (50-60 Hz) circuits up to 250V" 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 plugs and sockets to the BS 1363 standard. According to the IEC^[48] 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 (Type G)

BS 1363 rewirable plug

Comparison of moulded plugs. Schuko type weighing 47g and BS 1363 weighing 44g, both manufactured by Longwell Company

BS 1363 "13 A plugs, socket-outlets, adaptors and connection units"^[49] is the main plug and socket type used in the United Kingdom. According to the IEC^[40] it is also used in over 50 countries worldwide. Some of these countries have national standards based on BS 1363, including: Ireland, Malaysia, Malta, Singapore, and Saudi Arabia.

This plug, commonly called a 13 A plug or 13 amp plug, has three rectangular pins forming an isosceles triangle. The BS 1363 plug has a fuse which is suitably rated to protect the appliance's flexible cord from overload.

BS 4573 (UK shaver)

Main article: AC power plugs and sockets: British and related types § BS 4573 (UK shaver)

BS 4573 Plug

In the United Kingdom, Ireland, and Malta, there is a two-pin plug and socket for use with electric shavers and toothbrushes, defined by the BS 4573 standard.^[50] The plug has insulated sleeves on the pins. Shaver sockets are normally incorporated into shaver supply units which include an isolation transformer and meet the safety requirements of the BS EN 61558-2-5 standard.^[51] These are commonly found in bathrooms, and typically accept a variety of ~230 V two-pin plug types including BS 4573, Europlug Type C, and Australian two-pin plugs. The isolation transformer often includes a 115 V output to allow it to be used with a two-pin US Type A plug. These sockets are required by both standards to be marked with a shaver icon, and may optionally also be marked "shavers only".

CEE 7 standards

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, known simply as CEE 7. It was originally published in 1951, the 2nd edition was published in May 1963 and was last updated by Modification 4 in March 1983.^[52] CEE 7 consists of general specifications, plus a number of standard sheets for specific connectors.

A number of standards based on two round pins with centres spaced at 19 mm are in use in continental Europe and elsewhere, 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".^[53] There is no European Union regulation of domestic mains plugs and sockets, and the Low Voltage Directive specifically excludes domestic plugs and sockets.^[32] 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 wall socket, accepts CEE 7/2 (unearthed) plug and also CEE 7/4, CEE 7/6 and CEE 7/7 (earthed) plugs 

Power bar with CEE 7/1 sockets and CEE 7/2 plug 

CEE 7/4 plug partially inserted in CEE 7/1 non-earthed socket, pins are in contact but exposed. There is no connection for the earthing contact 

CEE 7/1 unearthed sockets are designed to accept CEE 7/2 round plugs without notches in the body and having 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. The regulations of countries using the CEE 7/3 and CEE 7/5 socket standards vary in whether CEE 7/1 sockets are still permitted in environments where the need for earthing is less critical. Sweden, for example, prohibited them from new installations in 1994. In Germany unearthed sockets are rare, whereas in the Netherlands and Sweden it is still common to find them in "dry areas" such as in bedrooms or living rooms. Some countries prohibit use of unearthed and earthed sockets in the same room, in the "insulated room" concept, so that people cannot touch an earthed object and one that has become live, at the same time.

The depth of the sockets varies between countries and age. Older sockets are so shallow that it is possible to touch the pins of a plug when the plug is inserted only deep enough to get electrical power on the pins, while newer sockets are deep enough to protect from this kind of accident. CEE 7/1 sockets 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 were specifically designed not to allow insertion of CEE 7/2 unearthed round plugs fitted to older appliances which had to be earthed via other means.

Two Schuko (CEE 7-3) socket-outlets manufactured by Busch-Jaeger Elektro GmbH, the lower has (black) protective shutters, the upper does not, revealing internal metal contacts.

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

Further information: Schuko

Schuko plug (CEE 7/4) and socket (CEE 7/3)

The CEE 7/3 socket and CEE 7/4 plug are commonly called Schuko. The socket (which is often, in error, also referred to as CEE 7/4) has a predominantly circular recess which is 17.5 mm (0.689 in) deep with two symmetrical round apertures and two earthing clips on the sides of the socket positioned to ensure that the earth is always engaged before live pin contact is made. The plug pins are 4.8 by 19 mm (0.189 by 0.748 in). The Schuko connection system is symmetrical and unpolarised in its design, allowing line and neutral to be reversed. The socket also accepts Europlugs and CEE 7/17 plugs. It is rated at 16 A. The current German standards are DIN 49441:1972-06 "Two-pole plugs with earthing-contact 10 A 250 V≅ and 10 A 250 V–, 16 A 250 V∼" (which also includes CEE 7/7 plug) and DIN 49440-1:2006-01 "Two-pole socket-outlets with earthing contact, 16 A 250 V a.c." In addition to Germany, it is used in Albania, Austria, Belarus, Bosnia and Herzegovina, Bulgaria, Chile, Croatia, Denmark, Estonia, Finland, Greece, Hungary, Iceland, Indonesia, Iran, Italy (standard CEI 23-50), Kazakhstan, Latvia, Lithuania, Luxembourg, Republic of Macedonia, Republic of Moldova, the Netherlands, Norway, Pakistan, Portugal, Romania, Russia,^[54] Serbia, Slovenia, South Korea^[55], Spain, Sweden, Turkey, Ukraine, and Uruguay.

Schuko is an abbreviation for the German word Schutzkontakt, which means "Protective contact" - in this case "protective" refers to the earth.

Some countries, including South Korea, Portugal, Finland, Denmark,^[56] Norway and Sweden, require child-proof socket shutters; the German DIN 49440-1:2006-01 standard does not have this requirement.

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

French socket

Rewireable French plug

The CEE 7/5 socket and CEE 7/6 plug are defined in French standard NF C 61-314 "Plugs and socket-outlets for household and similar purposes" (which also includes CEE 7/7, 7/16 and 7/17 plugs) The socket has a predominantly circular recess which is 15 mm (0.591 in) deep with two symmetrical round apertures and a round 4.8 mm (0.189 in) earth pin projecting from the socket such that the tip is 23 mm (0.906 in) beyond the live contacts, to ensure that the earth is always engaged before live pin contact is made. The earth pin is centred between the apertures, offset by 10 mm (0.394 in). The plug (which is often, in error, also referred to as CEE 7/5) 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 line and neutral and there is no universally-observed standard. However, the Czech standard recommends that the line wire be on the left side when facing the socket. The French convention changed circa 2002 from nothing particular, to, if the earth pin was at the top then the line hole in the socket would be on the right looking at the socket. However, the socket may not necessarily be installed with the earth pin at the top. Packaging in France of sockets is normally marked with correct connection of the cables. Polarised pre-fitted plugs on appliances are therefore connected with the brown line wire to the right pin and the blue neutral wire to the left, the earth being connected to the contact at the "top" of the plug.

CEE 7/2 and 7/4 plugs are not compatible with the CEE 7/5 socket because of the round earthing pin permanently mounted in the socket.

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

CEE 7/7 plug

To bridge the differences between German and French standards, the CEE 7/7 plug was developed. It is polarised to prevent the line and neutral connections from being reversed when used with a French CEE 7/5 socket, but allows polarity reversal when inserted into a German CEE 7/3 socket. The plug is rated at 16 A.

It has earthing clips on both sides to connect with the CEE 7/3 socket and a female contact to accept the earthing pin of the CEE 7/5 socket. Currently, appliances in many countries are sold with non-rewireable CEE 7/7 plugs attached, enabling use in all countries whose socket standards are based on either CEE 7/3 or CEE 7/5.

CEE 7/16 plugs

The CEE 7/16 standard sheet appears in Supplement 2 (June 1962) to the 1951 edition of CEE 7. The CEE 7/16 unearthed plug is used for low power Class II applications, 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. Although it is similar in appearance to CEE 7/17 it has narrower pins (4 mm) and a lower current rating (maximum 2.5 A). This alternative is seldom used.

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

Further information: Europlug

Example of a Europlug

Alternative II, popularly known as the Europlug, is a flat plug. It is also defined by Cenelec standard EN 50075 "Flat non-rewirable two-pole plugs, 2.5 A 250 V, with cord, for the connection of class II-equipment for household and similar purposes", which has national equivalents in most European countries, as described in IEC 60083. The Europlug is not rewirable and must be supplied with a flexible cord. Because it is unpolarised, it can be inserted in either direction into a socket, so line and neutral are connected arbitrarily.

Plugs and sockets are usually designed together, with the contacts of the socket part designed to accept the specific pin diameter, pin length, and pin spacing of the mating plug part. However, there is no socket defined by EN 50075; neither is there a socket specified in CEE 7 to accept only 4 mm (0.157 in) pins or the profile of a Europlug. (There are examples of sockets on the market which accept only such plugs, sometimes in multiples, but these meet no recognized standard.) Instead of being designed with a matching socket, the Europlug was designed to be compatible with a range of sockets in common use throughout mainland Europe. These sockets, including the CEE 7/1, CEE 7/3 (German/"Schuko"), CEE 7/5 (French), and 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.^[57] To improve contact with socket parts intended to receive pins having a diameter larger than 4.0 mm, the Europlug has two round, slightly flexible pins which converge slightly towards their free ends.

The Europlug is physically not compatible with BS 1363 13 A sockets, however most modern UK dedicated shaver sockets designed to accept BS 4573 shaver plugs also accept Europlugs for applications requiring less than 200 mA.^[58] Other than such personal hygiene applications, UK consumer protection legislation^[59] does not permit the supply of appliances fitted with Europlugs.

Apart from use in continental Europe, the Europlug is also used in the Middle East (Iran), most African nations, South America (Argentina, Bolivia, Brazil, Chile, Peru and Uruguay), Asia (India, Bangladesh, Sri Lanka, Indonesia, Pakistan, China, South Korea, Thailand, Philippines, Malaysia and Singapore) as well as Russia and the former Soviet republics, such as Ukraine, Armenia, Georgia, and many developing nations. Where permitted it is also used, by means of adaptors, in many nations, particularly former British colonies, which use the BS 1363 standard.

CEE 7/17 unearthed plug

CEE 7/17 plug

This is a round plug which conforms to a shape 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). It may be rated at either 10 A or 16 A, and 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 can be inserted into Israeli SI 32 with some difficulty. The Soviet GOST 7396 standard includes both the CEE 7/17 and the CEE 7/16 variant II plug.

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

Danish 107-2-D1, standard DK 2-1a, with round power pins and half round earth pin

Danish unearthed and switched socket

Socket for the tilted flattened pins and half-round earth pin of Danish computer equipment plug (mainly used in professional environment), standard DK 2-5a

This Danish standard plug is described in the Danish Plug Equipment Section 107-2-D1 Standard sheet (SRAF1962/DB 16/87 DN10A-R). Unlike the French CEE 7/6 plug, the earthing pin is on the plug, not in the socket^[60]. The Danish socket need not be recessed to protect the earthing pin. 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 don't fit into the special computer socket. The plug is often used in companies, but rarely in private homes.

There is a variation for hospital equipment with a rectangular left pin, 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 then 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 2-pin, female earth CEE 7/5 are permitted for installations in Denmark.^[61] This was done because no electrical equipment sold to private users is equipped with a Danish plug.

Sockets for the Schuko 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.

Denmark has allowed CEE 7/3 "Schuko" sockets since 15 November 2011.^[62]

Italy (Type L)

Side by side comparison of Italian CEI 23-50 S 11 and S 17 plugs and sockets rated 16 A (left) and 10 A (right).

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)^[63]. 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.

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).

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^[64] (for electromotive force, see above) or sometimes (inappropriately) industriale (industrial) or even calore.

Old adaptor from forza to 2 × luce and 1 × forza

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 single phase and 220 V single phase (from 3-phase 380 V) or two phase (from 220 V 3-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.^[65] 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)^[66] 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).^[67]

Italian multiple standard sockets

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^[68] 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).

Soviet standard GOST 7396 C 1 unearthed

This Soviet plug, still widely used in modern Russia, 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 French CEE 7/6 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.

• 
  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 CEE7/16, but has different configuration. Thermoplastic plug is rated 6 A and 250 V.

Swiss SEV 1011

Type J: The 10 Ampere SEV 1011:2009 type 13 socket (here: a triple socket) and type 12 plug

The Swiss standard, also used in Liechtenstein,^[69] is SN SEV 1011:2009 Plugs and socket-outlets for household and similar purposes.^[70] 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.^[71]

SEV 1011:2009, overview of the hierarchical Swiss System

The three phase variants of the standard are also described at Industrial and multiphase power plugs and sockets § Switzerland: SEV 1011.

All of the single phase connectors are rated at 250 V. The three-phase connectors are rated at 250 V (phase-to-neutral) / 400 V (phase-to-phase).

The Swiss standard does not require the use of child protective shutters.

The Swiss standard was first described in SEV 1011 (ASE1011/1959 SW10A-R). On 4 December 2009, the TK23 Technical Committee issued the new revised edition of the Swiss standard SEV 1011:2009 for 10-A plugs and 11/12 sockets to provide, among other things, improved protection against contact with partially insulated pins can. As of 1 January 2013, imports into Switzerland of Type 11 and Type 12 plugs are only permitted with partially insulated plug pins. After the year 2016, only sockets type 13 with a recessed socket hole may be brought onto the market.

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.^[76]

The plug and socket are rated 16 A 250 V a.c. and are intended for use only on systems having nominal voltages between 200 V and 250 V a.c. 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 left when looking at a socket with the earth pin offset down. 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.^[77][78]

Brazil developed a plug resembling IEC 60906-1 as the national standard under specification NBR 14136.^[45] The NBR 14136 standard has two versions, neither of which has pin dimensions or ratings complying to IEC 60906-1. Use at 125 V is permitted by NBR 14136, which is against the intention of IEC 60906-1.

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

Chinese 3-pin socket and compound socket which also accepts NEMA and Europlug (right), and a less common, larger 16 A version (left)

The standard for Chinese plugs and sockets (excluding Hong Kong and Macau) 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.^[79] 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; 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.

Israel SI32 (Type H)

Two Israeli plugs and one socket. The left plug is the old standard; the one on the right is the 1989 revision.

Socket polarity, with wire colour coding.

The plug defined in SI 32 (IS16A-R) is used only in Israel and in the territories of the West Bank and the Gaza Strip. There are two versions: an older one with flat pins, and a newer one with round pins.^[80]

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).^[80] 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.^[81]

North American and IEC 60906-2

Most of North America and Central America, and some of South America, use connectors standardized by the National Electrical Manufacturers Association. 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 amperage, 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. The prefix, L, is added for the locking types; a 15 A 120 V two-pole grounding plug is designated NEMA L5-15P. Twist-locking types are used for additional protection from accidental disconnection, or to prevent interchange with parallel blade types

For some configurations, the arrangement of pins will differ slightly for the different current ratings, to prevent accidental mating of devices with a higher current draw than the receptacle can support.

IEC 60906-2 is based on NEMA 5-15.

A brief description of some common NEMA standards appears below. A more comprehensive list, with more detail, appears in the NEMA connector article.

NEMA 1-15 ungrounded (Type A)

Polarized (left) and unpolarized NEMA 1-15 plugs

Main article: NEMA 1

NEMA-1 plugs, rated 15 A at 125 volts, are compatible with both NEMA-1 receptacles and NEMA-5 receptacles; NEMA-1 is ungrounded (no earth), while NEMA 5 is grounded. The plug has two parallel blades. Early versions were not polarized, but most plugs are polarized today via a wider neutral blade on the plug that fits a wider neutral opening on the receptacle. (Unpolarized AC adaptors are a common exception.)

Harvey Hubbell patented a parallel blade plug in 1913, where the blades were equal width (US patent 1064833^[82]). In 1916 Hubbell received a further patent for a polarized version where one blade was both longer and wider than the other (US patent 1180648^[83]), in the polarized version of NEMA 1-15 both blades are the same length, only the width varies.

Ungrounded NEMA-1 outlets are not permitted in new building construction in the United States and Canada, but can still be commonly found in older construction. Allowed replacement of NEMA-1 receptacles varies by local code.

NEMA 5-15 grounded (Type B)

NEMA 5-15 plug, left. Decorative-style duplex socket, with orientation as specified in NECA 130-2010, centre. Ordinary duplex socket, with orientation typically found, right. Photos are different scale – parallel blades are on 1/2 inch (12.7 mm) centres.

Main article: NEMA 5

The NEMA 5-15 plug has two flat parallel blades like NEMA 1-15, but also adds a ground (earth) pin.^[84] It is rated 15 A at 125 volts. The ground (earth) pin is longer than the line and neutral blades, so the device is grounded before the power is connected. Both current-carrying blades on grounding plugs are normally narrow, since the ground (earth) pin enforces polarity. NEMA 1-15 plugs are also compatible with NEMA 5-15 sockets.

The 5-15 socket is standard in Canada, the United States, Mexico and Panama. It is also used in Central America, the Caribbean, northern South America (Colombia, Ecuador, Venezuela and, as a legacy, parts of Brazil), Japan, Taiwan, the Philippines and Saudi Arabia. This socket is recommended in IEC standard 60906-2 for 120 volt 60 Hz installations. Looking directly at a NEMA 5-15 socket in the commonly found orientation of ground (earth) at the bottom, the neutral slot is on the left, and the line slot is on the right. However, in the US the National Electrical Installation Standards (NECA 130-2010)^[85] specifies that the ground hole should be on top. Sideways installation is also permitted; in this case, NECA 130-2010 specifies the neutral (long) slot is on top and the ground hole on the left..

In 46 of the 50 United States^[86] and all of Canada, tamper-resistant sockets are now required in new residential construction. These prevent contact by objects like keys or paper clips inserted into the socket.^[87]

In stage lighting, this connector is sometimes known as PBG for Parallel Blade with Ground (earth), Edison or Hubbell, the name of a common manufacturer.^[88]

NEMA 5-20

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.

As NEMA 5 currents increase, changes are made to the plug's neutral blade so that it will not fit into sockets rated for a lower current. Some sockets rated for higher currents are designed to accept many shapes for the neutral blade, so that both high and low draw devices are compatible with it.

The NEMA 5-20 AP variant has a horizontal neutral blade (in a plane that would intersect the hot blade). The receptacle has a T-slot for the neutral blade which accepts either 15 A parallel-blade plugs or 20 A plugs.

NEMA 5-30 and 5-50 are rare; L5-30 and L5-50 twistlock is more common. The non-locking versions are physically incompatible with 5-15 and 5-20, as the hot/neutral blades are farther apart.

JIS C 8303, Class II unearthed

Japanese socket with earth post, for a washing machine

Japanese socket with earth post and earth connector, for an air conditioner

Japanese 200 V socket with earth post, for an air conditioner

The Japanese plug and socket appear physically identical to NEMA 1-15. The Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by METI or JIS.^[89]

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 (East Japan) or 60 Hz (West Japan) depending on whether the customer is located on the Osaka or Tokyo grid.^[90][91] Therefore, some North American devices which can be physically plugged into Japanese sockets may not function properly.

Thai 3 pin plug TIS 166-2549

TIS 166-2549 plug

Thai Industrial Standard (TIS) 166-2547 and its subsequent update TIS 166-2549^[93] 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).^[94] The plug is similar to, but not interchangeable with, the Israeli SI32 plug. The Thai plug has not been designated with a letter code at IEC World Plugs,^[40] but is sometimes referred to and sold as "Type O".^{[95][96][97][98][99]}

Compatibility

Plugs of type D, G, and M are physically incompatible with any other type other than their own.
3-pin plugs of type H, J, K, L, N, and Thai are only compatible with sockets of the same letter type.
Not all plugs with a given letter are entirely compatible with a socket of the same letter.:

• Polarized A plugs will physically not fit into unpolarized A sockets.
• Type I sockets in Argentina vs. Australia & China are physically compatible, but have the reverse polarity, thus causing an electrical incompatibility.
• Sometimes the physical shape of the plug (especially when built into a device like an AC adapter) may cause the plug to be physically incompatible with the socket, or to prevent nearby sockets from being used.
• Various European-style plugs with two male pins fit a variety of 2 and 3-pin sockets, but compatibility is not complete across all types (see table).

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)

A lampholder plug fits into the bayonet cap or Edison screw socket of a lampholder in place of a light bulb and enables an electrical appliance to be powered from a wall or ceiling light fitting. As mentioned in Early History above, they were first introduced in the late 1800s and in use to the 1960s in situations where wall sockets were scarce and sometimes non-existent in some rooms (bathrooms, cellars, attics, etc.). Also, as in some countries (such as Italy) electricity was supplied on a "split tariff" basis with electricity for lighting being charged at a lower rate than that for other purposes, lampholder plugs enabled the consumers to reduce their electricity costs and were thus in broad use.

Lampholder plugs were and are rarely fused.

In the UK, lighting circuits are protected with a 5 A fuse or 6 A miniature circuit breaker.^[101] Wiring regulations in the UK and some other countries no longer approve lampholder plugs because of the risks of overheating and fire.

Edison screw lampholder adaptors (for NEMA 1-15 plugs) are still easily found and commonly used in the Americas.

NEMA 2‐15 and 2‐20

These unearthed plugs with two flat parallel blades are intended for use on 240 volt circuits. The 2‐15 has coplanar current blades, and is used for 240 V service at 15 A, while the 2‐20 has the blades at 90° relative to each other (one vertical, one horizontal) and is used for 240 V service at 20 A. NEMA 2 plugs and sockets are rare because they are unearthed and so, no longer permitted for new installations. They have no neutral. In some cases these plugs can be inserted into incorrect-voltage sockets. Prior to the adoption of the NEMA standard, a plug nearly identical to the 2‐20 was used for 120 V at 20 A. That obsolete plug would fit into 5‐20 and 6‐20 sockets, which supply different voltages, but will not fit a NEMA 2‐20 socket.

Soviet adaptor plugs

Soviet adaptor plug

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. This design was very useful, because the usual Soviet apartment of the 1960s had very few sockets, 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

Walsall Gauge 13 A plug (bottom) compared to regular BS 1363 plug

Unlike the standard BS 1363 plugs found in the UK, the earth pin is on a horizontal axis and the line 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 on parts of the London Underground for 110 V AC voltage supply.^[102] 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 on circuits powered from the standby generators to stop staff from plugging in unauthorised devices, e.g. kettles. They were also known to be used in some British Rail offices for the same reason.

Italian BTicino brand Magic security connector

Left: Bticino Magic Security socket, detail.
Centre: assortment of Magic Security sockets (in orange, the industrial three-phase type).
Right: assortment of Magic Security plugs.

This style of connector, produced by Italian manufacturer BTicino, appeared in the 1960s and was intended as an alternative to the Europlug or CEI 23-16 connectors then in use.^[103] The socket is an almost rectangular socket, with one or more lateral key pins and indentations to prevent inverting the polarised plug, or connecting plugs and sockets with different current ratings. At least four models were produced: three single-phase general purpose connectors rated respectively 10 A, 16 A and 20 A; plus a three-phase industrial connector rated 10 A; all of them have different key-pin positioning so plugs and sockets cannot be mismatched.^[104] 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 energized only when it is inserted fully into the socket.

On the left a BTicino Magic Security plug (10 A), on the right a type L to Magic Security plug adaptor

The obvious drawback of the system is that it is not compatible with Italian 10 A and 16 A plugs, as well as with Europlugs. As household appliances were never sold fitted with these security plugs and the use of adaptors would defeat all of the newly introduced safety features, once this system is adopted all standard plugs must be cut off and replaced with the appropriate security connector. However, the Magic security system had some success at first because its enhanced safety features appealed to customers; standard connectors of the day were considered not safe enough.^[103] The decline of the system occurred when safety lids similar to the Magic type were developed (Vimar Sicury^[105]) and then applied to standard sockets by third brands and by BTicino itself.

In Italy, the system was never definitively abandoned and, though very rarely seen today, is still marked as available in BTicino’s products catalogue,^[106] (except for the three-phase version, which stopped production 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.