Early history
When electricity was first introduced into the household, it was primarily used for lighting. At that time, many electricity companies operated a split-tariff system where the cost of electricity for lighting was lower than that for other purposes. This led to portable appliances (such as vacuum cleaners, electric fans, and hair driers) being connected to the light fitting.
However, as electricity became a common method of lighting houses and operating labour-saving appliances, a safe means of connection to the electric system other than using a light socket was needed. The original two pin electrical plug and socket were invented by Harvey Hubbell and patented in 1904. Other manufacturers adopted the Hubbell pattern and by 1915 they were widespread, although in the 1920s and even later, household and light commercial equipment was still powered through cables connected with Edison screw-base adapters to lampholders.
The grounded consumer plug was invented by Albert Büttner, who patented the Schuko-system in 1926. The American version of the grounded plug, the three-prong plug was invented by Philip F. Labre, while he was attending the Milwaukee School of Engineering .It is said that his landlady had a cat which would knock over her fan when it came in the window. When she plugged the fan back in, she would get an electric shock. Labre figured out that if the plug were grounded, the electricity would go to earth through the plug rather than through his landlady. He applied for and was issued a US patent for grounding receptacle and plug on June 5, 1928. As the need for safer installations became apparent, earthed three-contact systems were made mandatory in most industrial countries.
Proliferation of standards
During the first fifty years of commercial use of electric power, standards developed rapidly based on growing experience. Technical, safety, and economic factors influenced the development of all wiring devices and numerous varieties were invented. Gradually the desire for trade eliminated some standards that had been used only in a few countries. Former colonies may retain the standards of the colonising country, occasionally—as with the UK and a number of its former colonies—after the colonising country has changed its standard. Sometimes offshore industrial plants or overseas military bases use the wiring practices of their controlling country instead of the surrounding region. Hotels and airports may maintain receptacles of foreign standards for the convenience of travellers. Some countries have multiple voltages, frequencies and plug designs in use, which can create inconvenience and safety hazards.
Design for safety
Design features and aspects of plugs and sockets have evolved to reduce the risk of electric shock and equipment damage. Depending on the plug/socket system, safety measures may include pin and slot configuration to permit only the correct insertion of plug into socket, earth pins longer than power pins so the device becomes earthed before power is connected, insulated pin shanks to reduce or eliminate live-contact exposure when a plug is partially inserted in a socket, socket slot shutters that open only for the correct plug, as well as inbuilt fuses and switches.
Consolidation of standards
In recent years many countries have settled on one of a few de facto standards, which became formalised as official national standards, although there remain older installations of obsolete wiring in most countries. Some buildings have wiring that has been in use for almost a century and which pre-dates all modern standards.
There has been some movement towards consolidation of standards for international interoperability. For example, the CEE 7/7 plug has been adopted in several European countries and is compatible with both Type E and Type F sockets, while the unpolarised Europlug is compatible with an even greater proportion of European and other socket types. IEC 60906-1 has been proposed as a common standard for all 230-V plugs and sockets worldwide but has only been adopted in Brazil to date.
Many manufacturers of electrical devices like personal computers have adopted the practice of putting a single world-standard IEC connector on the device, and supplying for each country a power cord equipped with a standard IEC connector on one end and a national power plug at the other. The device itself is designed to adapt to a wide range of voltage and frequency standards. This has the practical benefit of reducing the amount of testing required for approval, and reduces the number of different product variations that must be produced to serve world markets.

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