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The standard, Class 1 grounded mains plug used in Germany, Australia, the Netherlands, Sweden, Norway and Finland is known as CEE 7/4 (also known as "Shuko") It has two 4.8mm round contacts on 19mm centres and two grounding clips on the sides of the connector body. Because the CEE 7/4 plug can be inserted in either direction into the receptacle, the Shuko connection system is unpolarized (i.e. line and neutral are connected at random).
The CEE 7/7 plug was developed to bridge the differences between the "Shuko" plug/socket system and the connection system used in France and Belgium (see explanation below). It is used in applications up to 16 amps. Above that, equipment must either be wired permanently to the mains or connected via another higher power connector such as the IEC 309 system. This plug is also unpolarized except when it is used in French and Belgian sockets.
France and Belgium have standardised on a socket which is not compatible with the CEE 7/4 socket that it standard n Germany and other continental European countries. The reason for incompatibility is that grounding in the French/Belgian socket is accomplished with a round male pin permanently mounted in the socket. As mentioned above, the CEE 7/7 plug bridges the differences between the two types of sockets: It has grounding clips on both sides to mate with the CEE 7/4 socket and a female contact to accept the grounding pin of the French/Belgian socket. Note that the CEE 7/7 plug is polarized when used in the French and Belgian electrical system.
DENMARK (220-230VAC/50Hz)
The Danish standard us described in Afsnit 107-2-D1 and is used only in Denmark. The Danish socket will also accept either the CEE 7/4 or CEE7/7 plugs: however, there is no grounding connection with these plugs because a male ground pin is required on the plug. The correct plug must be used in Denmark for safety reasons. 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 amps.
ITALY (220-230VAC/50Hz)
The Italian grounded plug/socket standard, CEI 23-16/VII, includes two styles rated at 10 and 16 amps and differ in terms of contact diameter and spacing. Because they can be inserted in either direction at random, they are unpolarized. The Italian connector system is relatively standardised in Libya, Ethiopia, and Chile and is found randomly throughout North Africa.
Switzerland has its own standard which is described in SEC 1011. This connector system is rated for use in applications up to 10 amps. Above 10 amps, 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.
The standard 2-wire plug used in Class II, ungrounded, applications is popularly known as the Europlug which is described in CEE 7/16. This is probably the single most widely used international plug. It will mate with any socket that accepts 4.0-4.8mm round contacts on 19mm centres. It is commonly used in all countries of Europe except the United Kingdom and Ireland. It is also used in various parts of the developing world. This plug is generally limited for use in Class II applications that require 2.5 amps or less. It is, of course, unpolarized.
The Soviet Republics use a standard plug and socket defined in Russian Standard Gost 7396 which is similar to the Shuko (German) standard. Contacts are also on 19mm centres, but the diameter of this contact is 4.0mm compared to 4.8mm which is standard in Continental Europe.

In the Eastern European countries, the situation is changing and reliable information is still difficult to access. Many official standards are virtually identical to the Shuko 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 confirm to the Shuko standard. It appears that most if not all of the Eastern European countries generally use the Shuko 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. It is recommended that manufacturers utilise the standard Shuko plug when exporting products to these countries.

British Standard BS 1363 requires use of a 3-wire grounded and fused plug for all connections to the power mains (including Class II, two wire appliances) British power outlets incorporate shutters on line and neutral contacts to prevent someone from pushing a foreign object into the socket. The plug is rated at 3-13 amps, depending on the fuse. BS 1363 was published in 1962 and since that time it has gradually replaced the earlier standard plugs and sockets (BS 546). It s used throughout the United Kingdom, Ireland, Hong Kong, Malaysia and also in Singapore.
Australia’s standard plug/socket system is described in SAA document AS 3112 and is used in applications up to 10 amps. A plug/socket configuration with rating at 15 amps (ground pin is larger) is available. A plug and socket rated at 20 amps (all three pins are larger) are available on special order. The Australian system is also standard in New Zealand and Papua New Guinea. Although there are slight differences, the Australian plug mates with the socket used in the Peoples Republic of China (Mainland China)
INDIA (220VAC/50Hz)
India has standardised on a plug which was originally defined in British Standard 546 (the standard in the United Kingdom before 1962). It is rated at 15 amps and is also used in Nepal, parts of Southern Africa, and other areas electrified by the British.
ISRAEL (220VAC/50Hz)
Israel’s standard plug, defined in SI 32, is unique to Israel and is incompatible with all other plugs. It is rated at 16 amps.
JAPAN (100VAC, 50 & 60Hz)
The Japanese plug and socket on first glance is identical to the North American NEMA 5-15 standard. However, the Japanese system which is described in JIS 8303 incorporates tighter dimensional requirements, different marking requirements, and mandatory testing and approval by MITI or JIS. Furthermore, standard wire sizes and the resultant current ratings are different than those used elsewhere in the world.

In addition, Class I grounded sockets are used less frequently in Japan than in the U.S with the result that most appliances sold in Japan use a class II, ungrounded plug. Class I grounded appliances should be sold with a round wire adapter.
The standard NEMA 5-15 plug and socket system (in Canada, CS22.2, No.42) that is commonly used in the U.S and Canada is also an important international standard. In addition to North America, it is standard in Central America, Colombia, Venezuela and Ecuador whenever Class I, grounded connections are used. (Note, however, that most electrical systems in developing countries are usually ungrounded) This plug is rated at 15 amps. Other NEMA plug and socket configurations permit power connections at higher amperage and voltage ratings.
The standard NEMA 6-15 plug and socket system is designed specifically for 250V circuits. This pair has a straight blade configuration but NEMA calls out a system of locking pairs as well.
Information on electrical systems used in developing countries is imprecise at best. Formal electrical standards, where they exist at all, frequently do not cover plugs and sockets or are ignored in the market place. Furthermore, with regards to voltages and frequencies, power generating and distribution systems have been installed at various times by different contractors. These systems occasionally produce power at different frequencies and provide for final distribution at different voltages. Therefore, some cities - even individual buildings in those cities - may be supplied by two or more generating plants and power distribution systems, each with a different single-phase voltage and frequency. Most third world electrical distribution systems are ungrounded, hence three-contact, grounded plugs, while mateable with the sockets, are not necessarily providing the expected equipment ground. Alternative methods of equipment ground is advisable in these cases.
An ungrounded version of the North American NEMA 5-15P plug is commonly used in Central America and parts of South America. It is therefore common for equipment users to simply cut off the ground pin s that the plug can be mated with a 2 pole ungrounded socket.

Another common international standard is an ungrounded version of the Continental European (German "Shuko" standard).