Gourt Home::Gourt :: Domestic AC power plugs and sockets
Domestic AC power plugs and sockets allow a connection between the mains electricity (household, usually single-phase, AC electrical power) and the appliances commonly used in homes.
A power plug (mains plug) is a connector that fits into a power point or electrical socket. It has male features, usually brass and often tin or nickel plated, which interface mechanically and electrically to the mains. Such plugs have a live contact, a neutral contact, and an optional earth (also known as ground or safety ground). In many types of plugs there is no distinction between live and neutral and in a few cases both main pins may be live.
A power socket (electrical socket, power point, mains socket, plug-in, outlet, receptacle, or female power connector) is a connection point that delivers mains electricity when a plug is inserted into it. It is the opposite of a plug, and usually has only female features.
Most common household power is "single phase". In some countries two live conductors (split phase or two phases from a three phase supply) or even three phases are wired into a home. However in most places only one phase conductor along with the neutral is connected to each household socket. Sockets for three-wire 120/240 volt appliances, with two live connections, a neutral, and ground, are also common in North America.
The sections of this article on individual plug types cover only single-phase plugs and sockets for common domestic use. For plugs used for mainly industrial applications or with more than two current carrying conductors (split phase and 3 phase) see Industrial & multiphase power plugs & sockets; for other mains plug and sockets please see unusual and obsolete plugs and sockets.
| Standard wire colours for plugs | |||
|---|---|---|---|
| live | neutral | protective earth | |
| EU, 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 | |||
| 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
Live
The live contact carries alternating current. The voltage varies by country, as set by national regulations and industry standards. In some cases (North American split phase 240 volt circuits, older installations in Scandinavian countries, the outputs of British 110 V building site isolation transformers and probably a few other cases) both main conductors may be live, either being two phases from a three-phase system or being from a single-phase transformer with centre-tapped output. 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 mate one way round in some countries it may be common to wire them without regard for which is which.Neutral
The neutral contact is in most (but not all) cases referenced to the earth. Except under fault conditions it generally does not pose a danger, but is nevertheless treated as live in most installation practices.The main danger that can be posed by the neutral is it has a non-null voltage (possibly as high as the voltage on the mains line) after a broken neutral cable in the wiring. Neutral and earth (ground) are strongly related and are usually connected at some point. However extra connections between the Neutral and the Ground must not be made unless the relevant jurisdiction's regulations allow it. Connecting neutral and ground at more than one point can create a dangerous ground loop in the system.
Earth
The earth contact is only intended to carry 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). If a bare live wire or live component in a device gets loose and touches the metal casing of the appliance, somebody touching the case may receive an electric shock. In many countries devices with metal cases must have the case connected to the ground connection. This reduces but does not eliminate the voltage present on the case relative to earth and metalwork connected to the earthing system.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.
Alternative terminology
In the United States, "mains" power is referred to as line power (because it comes from the power lines). The live contact may be called live or hot. The neutral contact may be called cold, neutral, the grounded conductor, or, most technically, the identified conductor (the term used in the National Electrical Code). The earth contact is called ground or the grounding conductor.
In Australia, the live contact is called active.
In the United Kingdom the word "line" is occasionally used to denote the live terminal or wire. This terminology derives from its being at 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.
History of plugs & 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.
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 & voltage/frequency
The outline maps below show the different plug types, voltages and frequencies used around the world, colour-coded for easy reference.
See also List of countries with mains power plugs, voltages and frequencies for specific places.
Types of plug & sockets
Electrical plugs and their sockets differ by country in shape and size. Each type is designated by a letter, following US government practice, plus a short comment in parentheses giving its country of origin and number of contacts. Subsections then detail the subtypes used in various 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
Early examples were symmetrical, but later sockets and most newer plugs distinguish the neutral conductor by making it slightly wider than the hot one. Such newer plugs often will not fit in old sockets, but both versions fit in type B sockets. Some devices that meet strict standards, 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.
- NEMA 2-15, and 2-20
- JIS 8303, Class II
Furthermore, standard wire sizes and the resulting current ratings are different from those used elsewhere in the world. Some of these outlets are also symmetrical (non-polarized) — the holes in the sockets are the same size as the smaller hole on newer North American type A (and also B) sockets, and the blades on the plugs match this.
Japanese devices should be able to fit into a North American outlet without trouble, but North American appliances with polarized plugs may require an adaptor or a replacement non-polarized plug to be able to mate with a Japanese outlet (especially if the device in question has a grounding pin).
The ungrounded, polarized two-pin socket shown above is a Japanese socket manufactured by Matsushita Electric (National brand) for use in Japan.
Type B (American 3-pin)
- NEMA 5-15 / CS22.2, Nº42
There is a common variant, the 5-20, providing 20A. In this design, the left (neutral) blade is rotated 90 degrees. The mating outlet may use a "T-slot" design for the neutral side and so will also accept a regular NEMA 5-15. This service is commonly found in hospitals, small industry, and is becoming popular in many household kitchens because people often plug two high power appliances into one duplex receptacle. Because it has worked well in the United States, it is now being adopted in Canada as well, as an alternative to split duplex 15A outlets. This type is pictured below. It will accept NEMA 2-20 plugs; however, the devices will not work, because of the insufficent voltage.
There is also a 30A version of the 120V plug and 240V versions in all current ratings with different arrangements of pin directions. The 120V 30A plug is rare the 240V versions are often seen in better equipped workshops and used to power heaters and air conditioners. There are also special connectors used when an appliance requires connection to both hot lines and the neutral.
An adaptor, sometimes called a "cheater plug" or "ground lift", may be used to insert a grounded plug into a two-pin socket. In order for the ground connection to remain effective, the ground tab should be attached to ground, If the outlet box is grounded (see below) this can be done by screwing the metal tab to the fixing screw on the socket. However, most people don't bother with this extra step and it is pointless to do it with two-pin sockets on non-earthed circuits. In some countries it is common to just cut the earth pin off instead, this is no more immediately dangerous than using an ungrounded cheater plug but leaves the appliance permanently without its ground even if the installation is updated.
Outlet boxes in older installations are often grounded via the cable armor but there is no guarantee of the quality of that ground, making the use of these adapters potentially hazardous. The most-proper way to convert an obsolete type A outlet to a safer type B is to install new cable and a NEMA 5-15 receptacle. Another accepted alternative is to replace the outlet with a ground fault circuit interrupter (GFCI) outlet, which doesn't need a ground because it will trip on any circuit leakage. These are quite cheap in North America.
Because portable air conditioners cause many electrical fires, those sold in the United States now must have Leak Current Detection and Interuption (LCDI) plugs. The cords have a fine wire mesh around the conductors and circuitry to detect any current leaking from the conductors to the mesh, which would happen if the cord was damaged or frayed. These could be NEMA 5-15, 5-20, 6-15, 6-20 or 6-30 plugs depending on the air conditioner. The plug is equipped with "Test" and "Reset" buttons on the housing.
- JIS 8303, Class I
Type C (European 2-pin)
- CEE 7/16 (Europlug)
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
.
- BS 4573
- Sockets
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 previousy 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
- CEE 7/4
- Gost 7396
- CEE 7/7
- BS 1363
This plug, most commonly known as a "13-amp plug", has three rectangular prongs that form a triangle. Live and neutral are 4 × 6 × 18 mm with 9 mm of insulation (the insulation ensures that even small fingers cannot touch any live part of the prongs while unplugging an appliance), and spaced 22 mm apart. Earth is 4 × 8 × 23 mm.
BS 1363 plugs are required by the standard to be three pin and fused. The earth pin is required as it is used to open the shutters over the live and neutral pins on most sockets. The shutter prevents accidental contact with the live socket by (say) a child with a nail, and also discourages the use of two-pin unfused plugs made to other standards (it is possible to open the shutters with a tool like a screwdriver to allow the plug to be inserted but this is not recommended). On factory-fitted plugs for class II two-wire appliances, the earth pin is often plastic.
The fuse is required to protect the flex, as British wiring allows high-current circuits; without the fuse the flex is not considered to be sufficiently protected. Accepted practice in the UK is to choose from the commonly available ratings (3 A, 5 A, and 13 A) the smallest rating that will allow for the appliance's peak power consumption. Using a 13 A fuse on an appliance with thin flex is considered extremely bad practice in the UK but is still better protection than the flexes of those appliances would get in most other countries.
BS 1363 was published in 1962 and since that time it has gradually replaced the earlier standard plugs and sockets (type D) (BS 546). Despite being capable of carrying a maximum load of only thirteen amperes (as opposed to 15 or 16 amperes for some other types of plug), it is considered a very safe system and is used in the UK and many of its former colonies.
Type H (Israeli 3-pin)
- SI 32
- AS 3112
- CPCS-CCC
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. The Chinese and Australian plugs also differ in the respect that Live and neutral are reversed
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
- SEV 1011
- IEC 60906-1 – international standard 230 V plug
- DS Afsnit 107-2-D1
- CEI 23-16/VII, 10 A style (IT10A-R) plug
- CEI 23-16/VII, 16 A style plug
- Sockets
- Connecting live wire to the ground contact - LETHAL DANGER. 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. As mentioned above in the article, some countries and older installations have unearthed outlets. It is common to connect earthed appliances to these outlets either using an adaptor, using a European plug type with an earth contact that is not a pin or simply cutting the earth pin off. 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. In other cases, this may place the line switch in the neutral wire, leaving portions of the device energized 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. However TT systems are supposed to be RCD protected anyway so the most likely outcome is an immediate trip of the RCD. 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.
- BS 1363
- Common electrical adaptors in Hong Kong and the United Kingdom
- Common electrical plug and socket problems in Hong Kong
- 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
- National Electrical Code (US)
- Power connector
- Power cord
- Power strip
- Protective multiple earthing
- Telephone plugs
- 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 *
- 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
- A company that supplies solutions for plug and socket issue for export
- 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
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)
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".
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 & F hybrid
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)
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)
There are several AS/NZS 3112 plug variants 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 by 2005. However, equipment and cords made before 2003 can still be used.
This plug is similar in appearance to the Australian and Chinese plugs. The pins are 1 mm longer than those of the Australian version and there are slight differences in the specified body dimensions.
The most important difference lies in how the Argentine 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.
Type J (Swiss 3-pin)
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.
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 *. Brazil — which uses so far a mix of Schuko, Italian 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)
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.
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.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.
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 as above; its disadvantage is that it is twice as large as a plain type L socket.
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
Inexpensive testers are available to verify proper outlet wiring. However, these cannot detect if neutral and earth connections have been swapped with each other and they cannot detect if the earth is adequate for the installation design. Some exist that can give a crude measurement of EFLI, but still require knowledge of the installation type to determine whether the indication given is acceptable or not. Testers can also give misleading results (such as detecting a lost neutral as a live/earth swap). For these reasons, while they are useful as a quick test for common faults they should not be regarded as a substitute for testing the wiring with proper equipment and knowledge.
The possible wiring errors
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 possible errors are:Use of travel adaptors
Travel adaptors are commonly available to connect different plug and socket types. Use of these on a permanent basis is not advisable as they often have thinner than normal pins to fit a variety of socket types (and thus are more vulnerable to falling out, overheating etc). Also such adaptors will often not provide an earth connection so sticking to class 2 (double insulated) equipment is advisable unless there is no other option. They will also often cause live-neutral reversal which may be an issue with some equipment (see above).Safety note for mainland European plug types C, E, F, J, K, & L
Many European countries use the same basic two-pin plug designs but extended them to be earthed in different ways. Thus it is fairly common to find plug and socket combinations where the live and neutral pins will mate, but the earth pin will not. This also applies if a European plug is forced into a UK socket. Earth connections on European sockets are also sometimes absent or unreliable in old installations, especially where earthed sockets have been installed on older electrical installations that did not have earth connections.Safety note for developing countries
Formal standards may be completely absent, or at least not enforced. Voltages and frequencies may vary greatly, by location or over time. Power supply and transmission is often very unreliable. Villages may have no power supply at all. In towns and cities, different voltages and frequencies may be supplied to the same building. Earth contacts, where they exist, may not really be connected to the ground. Safety features should not be trusted unless verified. Caution is advised. The best solution for reliable constant voltage, constant frequency power, is to use a power conditioning Uninterruptible power supply with a built in circuit breaker or Fuse (electrical).Safety note for users in Hong Kong, the British Isles and other places that use British wiring methods
Opening the shutters with a screwdriver or similar object to insert a plug from another country is not advisable - it is unsafe to connect equipment to British wiring without the protection of a BS 1362 plug fuse. Also, Schuko and French plugs will not establish an earth connection. When selecting an adaptor to connect an appliance from another country to the UK electrical system care should be taken to ensure that the adaptor is BS-1362-fused and (if the appliance is earthed) that the earthing arrangements of the adaptor are suitable for the plug. The adaptor must also comply with relevant British Standards (BS 1363 or BS 5733).Safety note for modifications
If a plug does not mate with the sockets available, do NOT modify either and only replace one if you are sure you know what you are doing. Even if the modifications "work" (that is, operates initially) there is no guarantee the setup is safe. Safety features are easily missed until a fault occurs, and then it is, ipso facto, too late.Placement of outlets
Electrical outlets have become ubiquitous in modern buildings. They can be found in almost any building, and occasionally in some vehicles or outdoors. Building codes often place restrictions on the number or placement of electrical outlets. Rooms designed for certain purposes, such as computer labs or experimental labs, may require a lot of powered devices, and thus have unusually large numbers of wall outlets.
Outlets in unusual locations are often covered to protect them from the elements. This includes floor outlets and outdoor outlets. These are often used in schools for added safety as well as convienience.
See also
References
External links
Electric power | Mains power connectors | Standards
230 volt stik | Steckverbinder | Prise électrique | Spina elettrica | Elektros lizdas | Stopcontact | 配線用差込接続器 | Tomada elétrica | Nối điện xoay chiều dân dụng | Розетка (штепсельная коробка)
"Domestic AC power plugs and sockets"