AC power plugs and sockets: Difference between revisions
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Revision as of 17:43, 24 September 2006
Domestic AC power plugs and sockets are devices that connect the home appliances and portable light fixtures commonly used in homes to the commercial power supply so that AC electric power can flow to them.
Power plugs are male electrical connectors that fit into female electrical sockets. They have contacts that are pins or blades which connect mechanically and electrically to holes or slots in the socket. Plugs usually have a live or hot contact, a neutral contact, and an optional earth or ground contact. Many plugs make no distinction between the live and neutral contacts, and in some cases they have two live contacts. The contacts may be brass, tin or nickel plated,
Power sockets are female electrical connectors that have slots or holes which accept the pins or blades of power plugs inserted into them and deliver electricity to the plugs. Sockets are usually designed to reject any plug which is not built to the same electrical standard. Some sockets have one or more pins that connect to holes in the plug.
This article covers only plugs and sockets intended for common domestic use. For plugs and sockets used for industrial applications, or with more than two current carrying conductors, see Industrial & multiphase power plugs & sockets. For less common plugs and sockets see unusual and obsolete plugs and sockets.
| Standard wire colours for plugs | |||
|---|---|---|---|
| Region | Live | Neutral | Protective earth |
| EU,UK, Australia & South Africa (IEC 60446) | brown | blue | yellow & green |
| UK, Ireland & Australia before 1969 | red | black | green |
| United States and Canada (screw colour) | black (brass) | white (silver) | green (green) |
| Standard wire colours for wall sockets | |||
| Region | Live | Neutral | Protective earth |
| EU (IEC 60446) | brown or black | blue | yellow & green |
| Note: the colours above represent current European practice but older installations may be to previous national standards. | |||
| UK & Australia | brown or red (on older installs) | blue or black (on older installs) | green/yellow (core is usually bare and should be sleeved at terminations) |
| United States and Canada | black (or red) | white | green or bare |
The three contacts
In most countries, household power is single-phase electric power, in which a single live conductor brings alternating current into a house, and a neutral returns it to the power supply. North American electricity is a more complicated split phase system in which two live conductors bring current into the house and a single neutral returns it. Despite that, most household sockets have only a single live conductor.
Live or Phase
The live contact (also known as phase, hot or active) carries alternating current from the power source to the equipment. The voltage varies by country, as set by national standards. In some installations, there may be two live conductors, either being two phases from a three-phase system or being both phases from a split phase system. Some plug/socket combinations are designed in a way that a plug can be inserted only one possible way — this is referred to as a polarized plug (not to be confused with positive and negative polarity). Others allow the plug to be inserted with live and neutral either way round — this is referred to as an unpolarized plug. Furthermore even if live and neutral can only connect one way, in some countries it is common to wire them without regard for which is which. This can be hazardous with some equipment in which the neutral is connected directly to the chassis.
Neutral
The neutral contact returns current from the equipment back to the power source or distribution panel. It is in most (but not all) cases referenced to the earth. Except under fault conditions it does not pose a danger because the voltage is close to zero, but is nevertheless treated as live in most installation practices because it can develop a high voltage under fault conditions.
The main danger posed by the neutral is the voltage can rise as high as the voltage on the live conductor if a broken neutral cable in the wiring disconnects the neutral but leaves the live conductor connected. Another possibility is that the live and neutral may be reversed or crossed by improper installation.
Neutral and earth (ground) are closely related and are usually connected at some point. However extra connections between the neutral and the earth should be avoided unless the relevant jurisdiction's regulations allow it. Connecting neutral and earth at more than one point can sometimes create a dangerous ground loop in the system.
Earth/Ground
The earth contact (known as ground in American English) is only intended to carry electric current when connected to equipment that has developed an insulation fault (except for EMI/RFI filters which do cause a small current down the earth). The earth connection was added to modern plugs because, if a live wire or other component in a device touches the metal casing, anybody touching the device may receive a dangerous electric shock. In many countries devices with metal cases must have the case connected to the earth contact. This reduces but does not eliminate the possibility of the case developing a high voltage relative to the earth and grounded metalwork.
The idea of "taking fault currents safely to earth" popular in laymans understanding of earthing (and worryingly school science books) is a misconception, the earthing system serves two purposes, firstly it provides a system to automatically cut the power to an appliance with a fault to the case and secondly it tries to hold all touchable metalwork that has a low impedance connection to anything at the same potential.
When the neutral is directly connected to the earth as part of the wiring system (a TN system) a fault to earth is a short circuit and therefore provided the wiring is done correctly the circuit breaker will open, or the fuse will blow. In the case of an indirect connection (via the body of the earth) between the earth and the neutral (a TT system) the resistance of the path is much higher and therefore a residual-current device (RCD) must normally be used to disconnect the fault.
The neutral core could in theory be used as a ground, but this would be dangerous if the core broke, so this is not normally used in building wiring or portable appliances. It is, however, used in some other situations with special precautions. For instance, in Switzerland, sockets in houses with the old two wire installation have the ground and neutral contacts connected together, probably supposing, that the professionally maintained house installation is much more reliable than plugged-in device. Also using the neutral as a ground prevents the use of RCDs.
Differences in terminology
There are significant differences between American English and British English in talking about power plugs and sockets.
| British | American | Meaning |
|---|---|---|
| mains power | line power | House electrical AC current |
| earth connection | ground connection | Safety connection to the earth or ground |
| flex | cord | Flexible electric cable from plug to appliance |
| socket | outlet, receptacle | Female part of an electrical connection |
| pin | prong | Male part of an electrical connector |
In the United States, the live contact may be called live or hot. The neutral contact may be called cold, neutral, the grounded conductor, or (in the National Electrical Code), the identified conductor. The earth contact is called ground or the grounding conductor.
In the United Kingdom the word "line" is occasionally used to denote the live terminal or wire. This terminology derives from its being at the line voltage relative to neutral and ground, as distinct from the "phase" voltage, between lines on different phases of the supply.
Live conductors are called phases when there is more than a single phase in use. Pins are also known as prongs, contacts or terminals.
In Australia, the live contact is called active.
History of plugs and sockets
When electricity was first introduced into the domestic environment, it was primarily for lighting. However, as it became a viable alternative to other means of heating and also the development of labour-saving appliances, a means of connection to the supply other than via a light socket was required. The electrical plug and socket were invented by Harvey Hubbell and patented in 1904.
At that time, some electricity companies operated a split-tariff system where the cost of electricity for lighting was lower than that for other purposes, which led to low-power appliances (for example, vacuum cleaners, hair driers) being connected to the light fitting. The picture to the left shows a 1909 electric toaster with a light bulb socket plug.
In 1928, the three prong plug was invented by Philip F. Labre, while he was going to school at MSOE (Milwaukee School of Engineering). The story goes that his landlady had a cat, the cat would knock over her fan when it came in the window and when she would plug the fan back in, she would get shocked. Philip figured out that if the plug was grounded, the electricity would be controlled. He applied for and was issued a patent for grounding receptacle and plug on June 5 1928.[1]
As the need for safer installations grew, earthed three-contact systems were developed.
The reason that there are now over a dozen different styles of plugs and wall outlets is that many countries preferred to develop plug designs of their own, instead of adopting a common standard. In many countries, there is no single standard, with multiple plug designs in use, creating extra complexity and potential safety problems for users.
However, as shown below, most countries have settled on one of a few common de facto standards; though there are legacy installations of obsolete wiring conventions in most regions of the world. Some buildings have wiring that has been in use for almost a century and which pre-dates all modern standards.
Many manufacturers of electrical devices, particularly personal computers, have adopted the practice of incorporating a world-standard IEC connector on the device and including a power cord equipped with a mating IEC connector on one end and the local power plug at the other.
World maps by plug/socket and voltage/frequency
There are two basic standards for voltage and frequency in the world. One is the North American standard of 110-120 volts at 60 Hz, which uses plugs A and B, and the other is the European standard of 220-240 volts at 50 Hz, which uses plugs C through M. Countries on other continents have adopted one of these two standards, although some countries use variations or a mixture of standards. The outline maps below show the different plug types, voltages and frequencies used around the world,[2] colour-coded for easy reference.
See also List of countries with mains power plugs, voltages and frequencies for specific places.
Types of plug and sockets
Electrical plugs and their sockets differ by country in shape, size, and type of connectors. The type used in each country is set by national standards legislation. [3] In this article each type is designated by a letter, plus a short comment in parentheses giving its country of origin and number of contacts. Subsections then detail the subtypes of each type as used in different parts of the world.
Note that IEC Class I refers to earthed equipment. IEC Class II refers to unearthed equipment protected by double insulation. See Appliance classes.
Type A (American/Japanese 2-pin)
- NEMA 1-15
As standardized by the U.S. National Electrical Manufacturers Association [4] and similar bodies in other countries, this simple plug with two flat parallel pins, or blades, is used in most of North America, Central America, South America, Japan, and the Caribbean on devices not requiring a ground connection, such as lamps and "double-insulated" small appliances. The corresponding sockets have been prohibited in new construction in the United States or Canada since 1965, but remain in place in many older homes and are still sold "for replacement use only". Type A plugs are still very common because they fit into type B sockets.
Early designs were symmetrical, but many modern ones prevent the neutral pin from being inserted into the live socket by making it wider than the live one, which is referred to as a polarized plug. (Note that this is not the same as positive/negative polarization in a direct current system.) New polarized plugs will not fit in old type A sockets, but both old and new type A plugs will fit in new type A and type B sockets. Some devices that do not distinguish between neutral and live, such as sealed electronic power supplies, are still sold with both pins narrow. When attaching a new polarized plug to a cord, it is useful to remember that the most common type of two-conductor cord for low-power use in North America has smooth insulation on the "hot" side and ribbed insulation on the "neutral" side.
- JIS 8303, Class II
The Japanese plug and socket are identical to NEMA 1-15. However, the Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by MITI or JIS. [5]
Some Japanese outlets are non-polarized — the slots in the sockets are the same size - and will only accept non-polarized plugs. Japanese plugs should be able to fit into North American outlets without trouble, but North American appliances with polarized plugs may require adaptors or replacement non-polarized plugs to connect to Japanese outlets.
Japanese standard wire sizes and the resulting current ratings are different from those used elsewhere in the world. Furthermore, Japanese voltage is only 100 volts - lower than American voltage - and the frequency in eastern Japan is only 50 Hertz instead of 60, so even if a North American plug can be inserted into a Japanese socket, it doesn't always mean the device will work properly.
Type B (American 3-pin)
- NEMA 5-15
The type B plug has two flat parallel pins with the same geometry as type A, and a round ground or earthing pin (American standard NEMA 5-15/Canadian standard CSA 22.2, Nº42).[4] It is rated at 15 amperes. The ground pin is longer than the two parallel pins so that the device is grounded before the supply is connected. The neutral jack in the type B socket is wider to accommodate polarized type A plugs, but the type B plugs often have both pins narrow, the ground pin enforcing polarity.
The 5-15 socket is standard in all of North America (Canada, the United States and Mexico). It is also used in Central America, the Caribbean, the west coast of South America, Japan, parts of Korea, and Taiwan.
With American and Canadian plugs, if you look directly at a socket with the ground socket at a bottom, the neutral slot is on the left, and the live slot is on the right. They may also be installed with the ground at the top or on either side, but the sockets going clockwise are always ground, neutral, live. The plug has the same connections going counterclockwise. If the plug is polarized, the widest pin is the neutral connector.
Due to the low power (1.8KW) availible from a 120V 15A socket a number of other NEMA connectors for higher currents and 240 V supplies are also commonly encountered in north american homes.
- JIS 8303, Class I
Japan also uses a Type B plug.[5] However it is less common than its Type A equivalent.
Type C (European 2-pin)
- CEE 7/16 (Europlug)
This two-wire plug is unearthed and has two round, 4 mm pins, which usually converge slightly. It is popularly known as the Europlug and is described in CEE 7/16.[6] This is probably the single most widely used international plug. It will mate with any socket that accepts 4.0 mm round contacts spaced 19 mm apart.
It is commonly used in all countries of Europe except the UK, Ireland, and (former) UK dependencies such as Malta. It is also used in Russia (GOST 7396) and in various parts of the developing world such as India and much of Africa. This plug is generally limited for use in class II applications that require 2.5 A or less. Because it can be inserted in either direction into the socket, it is symmetrical (that is, live and neutral are connected at random). This plug is also defined in Italian standard CEI 23-5.
- CEE 7/17
This symmetrical plug might also be categorised under E or F. It has two pins like 7/16, but they are 4.8 mm in diameter like types E and F, and also a round, plastic or rubber base that stops the plug being inserted into small sockets that 7/16 can fit into. Instead, only large round sockets such as those intended for types E and F can take it. The base has holes in it to accommodate both side contacts and socket earth pins. Class II applications. Also defined in CEI 23-5. It is commonly used on Class 2 appliances in South Korea.
- BS 4573
In the United Kingdom and Ireland, there is a special version of the type C plug for use with shavers (electric razors) in bath or shower rooms.[7] It has 5 mm diameter pins 16.6 mm apart, and the sockets for this plug can often take CEE 7/16, US and/or Australian plugs. They are also often capable of supplying either 230 V or 115 V. In wet zones, they must contain an isolation transformer compliant with BS 3535.
- Sockets
Some Type C sockets can only take 4 mm pins or have plastic barriers in place to prevent Schuko or French plugs from entering. However, many can take 4.8 mm pins and have plenty of room for a 4.8 mm pin round Schuko or French plug to be inserted.
Type D (Old British 3-pin)
- BS 546, 5 A
India has standardised on a plug which was originally defined in BS 546. It has three large round pins in a triangular pattern, and is now almost exclusively used in India, Sri Lanka, Nepal, Namibia, and Hong Kong. This type was also previously used in tandem with the 15 A version in South Africa, but was eventually phased out. However, this 5 ampere plug, along with its 2 A cousin, is sometimes used in the UK for centrally switched domestic lighting circuits, in order to distinguish them from normal power circuits.
- BS 546, 15 A
This plug is sometimes referred to as type M, but it is in fact merely the 15 A version of the plug above, which it resembles, though its pins are much larger: 7.05 mm × 21.1 mm. Live and neutral are spaced 25.4 mm apart, and earth is 28.6 mm away from each of them. Although the preceding type is standard in India, Sri Lanka, Nepal, and Namibia, the 15 A version is also used in these countries for larger appliances. Some countries like South Africa use it as the main domestic plug and socket type, where sockets almost always have an on–off switch built into them. The Type M is almost universally used in the UK for indoor dimmable theatre and architectural lighting installations. It is also often used for non-dimmed but centrally controlled sockets within such installations. The main reason for doing this is that fused plugs, while convenient for domestic wiring (as they allow 32 A socket circuits to be used safely), are not convenient if the plugs and sockets are in hard to access locations (like lighting bars) or if using chains of extension leads (since it is hard to figure out which fuse has blown). Both of these situations are common in theatre wiring. This plug is also widely used in Israel for air conditioners.
Type E (French 2-pin, female earth)
 |
 |
- French type E
France, Belgium, Poland, Czech Republic, Slovakia and some other countries have standardised on a socket which is not compatible with the CEE 7/4 socket (type F) that is standard in Germany and other continental European countries. The reason for incompatibility is that earthing in the E socket is accomplished with a round male pin permanently mounted in the socket. The plug itself is round with two round pins measuring 4.8 × 19 mm, spaced 19 mm apart and a hole for the sockets earth pin. It will accept Europlug and CEE 7/17 plugs.
As with the German plug below this plug will fit some other types of socket either easily or with force. However there is no earth connection with such sockets! Also in some cases if the plug is forced in, the socket may be damaged when the plug is removed.
Type F (German 2-pin, side clip earth)
- CEE 7/4
Plug F, known as CEE 7/4 and commonly called a "Schuko plug", is like E except that it has two earthing clips on the sides of the plug instead of a female earth contact. The Schuko connection system is, of course, symmetrical. The socket accepts Europlug and CEE 7/17 plugs. It is used in applications up to 16 amperes. Above that, equipment must either be wired permanently to the mains or connected via another higher power connector such as the IEC 309 system.
"Schuko" is an abbreviation for the German word Schutzkontakt, which means "Protective (that is, earthed) contact".
- Gost 7396
The countries of the CIS use a standard plug and socket similar to the Schuko standard. The CIS standard is in Russian Standard Gost 7396. Contacts are also 19 mm apart, but the diameter of these pins is 4.0 mm (like C) instead of 4.8 mm (E and F). It is possible to mate Russian plugs with Schuko outlets, but Russian sockets will not mate with type E and F plugs as the outlets have smaller hole diameters than the pins of type E and F. This socket accepts Europlugs, but does not accept CEE 7/17 plugs because they use the larger pin size.
Many official standards in Eastern Europe are virtually identical to the Schuko standard. Furthermore, one of the protocols governing the reunification of Germany provided that the DIN and VDE standards would prevail without exception. The former East Germany was required to conform to the Schuko standard. It appears that most if not all of the Eastern European countries generally use the Schuko standard internally but, until recently, they exported appliances to the Soviet Union with the Soviet standard plug installed. Because the volumes of appliance exports to the Soviet Union were large, the Soviet plug has found its way into use in Eastern Europe as well.
Type E and F hybrid
- CEE 7/7
In order to bridge the differences between sockets E and F, the CEE 7/7 plug was developed: it has earthing clips on both sides to mate with the CEE 7/4 socket and a female contact to accept the earthing pin of the type E socket. Nowadays, when appliances are sold with type E/F plugs attached, the plug is CEE 7/7 and non-rewirable. This means that the plugs are identical in countries like France and Germany: only the sockets are now different.
One is only likely to come across type E/F plugs that are not compatible with the other type if for some reason a cheap replacement plug has been attached to a cord that originally had another plug. Better-quality replacements are usually CEE 7/7 and are compatible with Schuko and French standard sockets.
Note that the CEE 7/7 plug is polarised when used with a type E outlet, but becomes symmetrical with a type F outlet. The plug is rated at 16 A. Above that, equipment must either be wired permanently to the mains or connected via another higher power connector such as the IEC 309 system.
Type G (British 3-pin)
- BS 1363
The BS 1363 plug[8], commonly known as a "13-amp plug", is a large plug that has three rectangular prongs forming a triangle. Live and neutral are 4 × 6 × 18 mm spaced 22 mm apart. 9 mm of insulation over the base of the pins prevents people from touching a bare connector while the plug is partly inserted. Earth is 4 × 8 × 23 mm.
The earth pin is required to open shutters over the live and neutral pins on most sockets to prevent children from inserting metal objects into them, and also prevents the use of plugs made to other standards. On plugs for Class II appliances that do not require an earth, the pin is often plastic.
The plug is unusual in that it has a fuse inside rather than relying on a circuit breaker in the distribution panel for protection. The fuse is required to protect the flex, as British wiring standards allow very high-current circuits to the socket. Accepted practice is to choose the smallest standard fuse (3 A, 5 A, or 13 A) that will allow the appliance to function. Using a 13 A fuse on an appliance with thin flex is considered bad practice.
BS 1363 was published in 1962 and since that time it has gradually replaced the earlier standard (type D) (BS 546). Despite being capable of carrying a maximum load of 13 A, it is considered a very safe system.
Type H (Israeli 3-pin)
- SI 32
This plug, defined in SI 32 (IS16A-R), is unique to Israel and is incompatible with all other sockets. It has three flat pins to form a Y-shape. "Live" and "Neutral" are spaced 19 mm apart. The type H plug is rated at 16 A but in practice the flat pins causes it to overheat when connecting large appliances. In 1989 the SI 32 was revised to use three round 4 mm pins in the same locations as the older standard. Sockets are manufactured to accept both flat and round pins in order to be compatible with both old and new plugs. This also allows the type H socket to accommodate type C plugs which are used in Israel for non grounded appliances. Older sockets, from about the 1970s have both flat and round holes for "Live" and "Neutral" in order to accept type C plugs. As of 2006, "pure" type H sockets (for 3 flat pins) that do not accept type C plugs are very rare in Israel.
This plug is also used in the areas controlled by the Palestinian National Authority in the West Bank and all of the Gaza Strip.
Type I (Australian/Chinese 2/3-pin)
- AS 3112
This plug, used in Australia, New Zealand, and Papua New Guinea, has an earthing pin and two flat pins forming an upside down V-shape. There is an unearthed version of this plug as well, with only the two flat V-aligned pins. These flat blades measure 6.5 × 1.6 mm and are set 30° to the vertical on a nominal pitch of 13.7 mm. Wall sockets almost always have switches on them for extra safety, as in the UK.
There are several AS/NZS 3112 plug variants, [9] including one with a wider earth pin is used for devices drawing up to 15 A; sockets supporting this pin will also accept 10 A plugs. Additionally, there exists a 20 A variant, in which all three pins are oversized and 25 and 32 A variants with the 20 A larger pins and the earthing pin forming an inverted "L" for the 25 A and a horizontal "U" for the 32 A (note that the 5 variants {10; 15; 20; 25 & 32 ampere sockets} will accommodate all the plugs that are equal or of a lesser current carring capacity but not a higher value; i.e. a 10 A plug will be accommodated by all sockets but a 20 A plug will only be accommodated by a 20: 25 and 32 A outlet).
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. As of 2003, the latest major update is AS/NZS 3112:2000, which mandated insulated pins [10] by 2005. However, equipment and cords made before 2003 can still be used.
- CPCS-CCC
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Although there are slight differences (the pins are 1 mm longer) the Australian plug mates with the socket used in the People's Republic of China (mainland China). The standard for Chinese plugs and sockets was set out in GB 2099.1–1996 and GB 1002–1996. As part of China's commitment for entry into the WTO, the new CPCS (Compulsory Product Certification System) has been introduced, and compliant Chinese plugs have been awarded the CCC (China Compulsory Certification) Mark by this system. The plug is three wire, grounded, rated at 10 A, 250 V and used for Class 1 applications.
In PRC, the sockets are upside down, relative to the Australian one shown in the picture. However the most important difference lies in how the plug is wired: the positions of the live and neutral contact pins are reversed from those of the Australian plug. With devices conforming to current standards this should not matter too much in practice as neutral is generally treated with the same care as live in appliance design. However with older or non-complying equipment, using for example single pole switches to break only the live conductor rather than both live and neutral, this difference can be dangerous.
PRC also uses American/Japanese "Type A" sockets and plugs for Class-II appliances. It should be noted that the voltage across the pins of a Chinese socket will always be 220, no matter what the configuration.
- IRAM 2073
The Argentinian plug is a three-wire, earthed plug rated at 10 A, 250 V defined by IRAM and used in Class 1 applications in Argentina and Uruguay.
This plug is similar in appearance to the Australian and Chinese plugs. The pin lengths and wiring are the same as those for the Chinese version. The most important difference is that the Argentinian plug is wired with the live and neutral contacts reversed from those of the Australian plug.
Type J (Swiss 3-pin)
- SEV 1011
Switzerland has its own standard which is described in SEV 1011. (ASE1011/1959 SW10A-R) This plug is similar to C, except that it has the addition of an earth pin off to one side. Swiss sockets can take europlugs (CEE 7/16). This connector system is rated for use in applications up to 10 amperes. There is also a variant for 16 A with 3 square pins but it is much less common. Above 16 A, equipment must be either wired permanently to the electrical supply system with appropriate branch circuit protection or connected to the mains with an appropriate high power industrial connector.
This type of socket can also be sporadically encountered in buildings in Spain, where they may be erroneously referred to as enchufes americanos — American sockets.
Switzerland also has a two-pin plug, with the same pin shape, size and spacing as the SEV 1011's live and neutral pins, but the hexagonal form factor is more flattened. It fits into both Swiss sockets (round and hexagonal) and CEE 7/16 sockets and is rated for up to 10 A.
- IEC 60906-1 – international standard 230 V plug
In 1986, the International Electrotechnical Commission published with IEC 60906-1 the specification for a plug that looks similar but is not identical to the Swiss plug. This plug was intended to become one day the common standard for all of Europe and other regions with 230 V mains. An effort to adopt it as a European Union standard was put on hold in the mid 1990s. [11] Brazil — which uses a mix of Europlug, Argentine and NEMA plugs — adopted it as national standard NBR 14136 in 2001 and it will be the only plug permitted to be sold with domestic appliances in Brazil from 2009.
Type K (Danish 3-pin)
- DS Afsnit 107-2-D1
The Danish standard is described in DS section 107-2-D1 (SRAF1962/DB 16/87 DN10A-R). The plug is similar to F except that it has an earthing pin instead of earthing clips. As well as its own plug the Danish socket can be used with CEE 7/16 (Europlug) or CEE 7/17 (Schuko-French hybrid without earth contacts) plugs. CEE 7/4 (Schuko), CEE 7/7 (Schuko-French hybrid), and french earthed plugs will also fit but should not be used as the earth contacts will not mate. A variation of this plug intended for use only on surge protected computer circuits has been introduced. The current rating on both plugs is 10 A.
Adapter plugs exist to facilitate connection of CEE 7/7 prongs to non-computer outlets. These usually don't sell at the local supermarket and thus visitors wishing to be "safe" should visit an electrician.
Since the beginning of the 1990s grounded outlets have been required in all new electric installations.
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Type L (Italian 3-pin)
The Italian earthed plug/socket standard, CEI 23-16/VII, includes two styles rated at 10 A and 16 A that differ in terms of contact diameter and spacing. Both are symmetrical, and thus can be inserted in either direction. CEE 7/16 (type C) unearthed plugs are also in common use, and standardized as CEI 23-5. Appliances with CEE 7/7 plugs are often sold in Italy, but not every socket can take them. Adaptors are commonly used to connect CEE 7/7 plugs to CEI 23-16/VII sockets.
- CEI 23-16/VII, 10 A style (IT10A-R) plug
The 10 ampere style extends CEE 7/16 by adding a central earthing pin. Thus, CEI 23-16-VII 10 A sockets can accept CEE 7/16 plugs (europlugs). This is the plug in the illustrations.
Outside of Italy, this plug is relatively standardised in Libya, Ethiopia, and Chile and is found randomly throughout North Africa, and occasionally in old buildings in Spain.
- CEI 23-16/VII, 16 A style plug
The 16 ampere style looks like a bigger version of the 10 A style. The pins are a couple of millimetres further apart, and all three are slightly thicker. The packaging on these plugs in Italy may claim they are a "North European" type. They were also referred to as industriale ("industrial") although this is not a correct definition.
- Sockets
Two types of sockets are in common use in modern installations in Italy. One type has a central round hole and two 8-shaped holes above and below: this design allows the connection of both styles of type L plugs (CEI 23-16/VII 10 A and 16 A) and of the type C CEE 7/16 plug. The advantage of this socket type is its small footprint.
The other type looks like a type F socket, but adds a central grounding hole. This design accepts CEE 7/7 (type E/F) plugs, in addition to type C and type L 10 A variant; its disadvantage is that it is twice as large as a plain type L socket. Some of these sockets have extra holes to also accept type L 16 A plugs.
Older installations often have sockets that are specific to either the 10 A or the 16 A style plug, requiring the use of an adapter in case the other style needs to be connected.
Type M (see D)
Type M is used to describe the 15 A version of D.
Multi standard sockets
Sockets that take all common two pin plugs are commonly seen in poorer countries without strong standards of their own. Sometimes one or more earth holes may also be present to allow one or more 3 pin plug types. However these will not work with the non pin earth connections of schuko and french plugs and may well not actually be connected to earth. Great care should be taken about voltage and grounding arrangements when using such outlets.
Safety notes
Despite the fact that it seems easy to connect a plug or socket, some mistakes may result in a working but highly dangerous installation. Also, an incorrectly wired socket or plug may cause safety problems in the whole house. The main issues are:
- Connecting live wire to the ground contact -- this is lethally dangerous. This is especially bad because even though it can kill a human being who touches the box, the device will still work and so it may go unnoticed.
- Not connecting the ground contact at all. Some countries and older installations have unearthed outlets. It is common to connect earthed appliances to these outlets by a variety of means. Since appliances with earth connections will generally only be single insulated this can mean that a single fault will make the case live. Nonetheless it remains common practice in many parts of the world.
- Swapping live and neutral wires. In some cases, this has no effect and not all countries even consider it an error. In other cases, this may place the line switch in the neutral wire, leaving portions of the device live at all times (which does not pose immediate danger but increases the risk of shock if there is another fault or if someone tries to work on the appliance). For screw-in line voltage lamps, this can also result in the shell of the lamp base being connected to the line, greatly increasing the risk of shock when changing light bulbs.
- Swapping ground and neutral wires. This can cause a number of issues. In a TT earthing system it will mean that significant current will go down the earth rod and may lead to significant voltages between the case of the appliance with the wires swapped and other appliances. In a TN-S or TN-C-S system immediate danger is unlikely but there is still the potential for danger if a neutral or earth wire also breaks. Finally combined with a live-neutral swap further back it could result in live being supplied to the earth pin.
- Not providing adequate overcurrent/short circuit protection resulting in a far greater possibility of fire in the event of a fault.
See also
- DC plugs
- Double insulated
- Electricity
- Electrical power
- Extension cable
- Ground and neutral
- Industrial and multiphase power plugs and sockets
- List of countries with mains power plugs, voltages and frequencies
- Power connector
- Power cord
- Power strip
- Telephone plugs
References
General
- The original content for this article came from http://users.pandora.be/worldstandards/electricity.htm.
- IEC/TR 60083: Plugs and socket-outlets for domestic and similar general use standardized in member countries of IEC. International Electrotechnical Commission, May 2004. This 359-page technical report describes all national standards for domestic plugs and sockets. Its 1963 predecessor, CEE Publication 7, covered only the plugs and sockets of continental Europe.
- IEC 60884: Plugs and socket-outlets for household and similar purposes. International Electrotechnical Commission. This international standard defines general safety and test requirements for domestic plugs and sockets, but not any particular shapes.
- IEC 60906: IEC system of plugs and socket-outlets for household and similar purposes. International Electrotechnical Commission. This international standard defines the domestic plugs and sockets that the IEC suggests as a potential future common world-wide standard.
- IEC 60906-1 defines standard 230 V plugs
- IEC 60906-2 defines standard 115 V plugs
- IEC 60906-3 defines standard 4-48 V low-voltage plugs
- Guidance Notes for the Electrical Products (Safety) Regulation (2001 Edition — with amendments), Electrical and Mechanical Services Department, Hong Kong [1]
Notes
- ^ U.S. patent 1,672,067
- ^ Electric Current Abroad, U.S. Department of Commerce, International Trade Administration (2002), http://www.ita.doc.gov/media/Publications/pdf/current2002FINAL.pdf
- ^ IEC/TR 60083, Plugs and socket-outlets for domestic and similar general use standardized in member countries of IEC, International Electrotechnical Commission (2006)
- ^ a b ANSI/NEMA WD6, Dimensional requirements for plugs and receptacles, National Electrical Equipment Manfacturers Assocation
- ^ a b JIS C 8303,Plugs and Receptacles for Domestic and Similar General Use,Japanese Standards Association (1993)
- ^ EN 50075 (1991), Specification for flat non-wirable two-pole plugs 2.5 A 250 V, with cord, for the connection of class II-equipment for household and similar purposes,European Committee for Standardization (CEN)
- ^ BS 4573 (1970),British Standard Specification for two-pin reversible plugs and shaver socket-outlets,British Standards Institution
- ^ BS 1363 (1995), 13 A plugs, socket-outlets and adaptors. Specification for rewirable and non-rewirable 13 A fused plugs, British Standards Institute
- ^ AS/NZS 3112 plug variants
- ^ insulated pins
- ^ http://www.iec.ch/zone/plugsocket/ps_history.htm
External links
- Hubbell History - Invention of the power plug and outlet.
- Australian AS/NZS 3112 mains plug description and wiring
- Australian AS/NZS 3112 mains plug with insulated pins
- Australian AS/NZS 3112 mains plug variants
- IEC Zone: Plugs and sockets
- AC Power Cords
- Glossary of standards organisations
- Steve Kropla's World Electric Guide
- http://www.starkelectronic.com/fzfv.htm
- Change to UK electrical wire colours 2004
- Household electrical safety handbook, Electrical and Mechanical Services Department, Hong Kong Special Administrative Region Government
- http://www.powerconnections.co.uk
- IEEE history of Australian power connectors (in MS Word format)
- Information on the electrical systems in use in most countries of the world
- International plug standards from travel-island.com
- Pictures and dimensions of various plug types