As a consequence, the market for electric light during the 1880s was extremely small, and the number of “ bulb receptacles” or sockets produced was minuscule. In 1919 Hubbell unsuccessfully attempted to get an injunction to prevent other manufacturers from making receptacles and plugs to the dimensions used by Hubbell. Hubbell’s parallel pin configuration was preferred, but Hubbell rebelled against standardization, and refused to agree, asserting that it had common law rights in the dimensions of its line. Gradually the desire for trade eliminated some standards that had been used in only a few countries.

This would have been a desirable feature in the days before wall receptacles became widespread and, for many consumers, the only source of electricity was an electric light socket. The reason why the world is now stuck with no less than15 different styles of plugs and wall outlets, is because many countries preferred to develop a plug of their own, instead of adopting the US standard. Because plugs are occasionally damaged due to accidents or rough use, the lighting partsare routinely replaced during the refurbishment of an electric lamp.The earliest American patent application for an earthed plug appears to be 11 January 1915 by George P. It wasn’t until 2007 that Brazil became the first country in the world to adopttype Nas its standard wall outlet and plug top.

Knapp’s design was obsoleted in the US before the modern National Electrical Manufacturers Association (NEMA) designations, but is still used in some other countries including China, Argentina and Australia. In 1986, the IEC finally presented the universal standard plug (type N) to the world, but unfortunately the initial enthusiasm had dampened. The existence of both “tandem” and parallel pin configurations had led to the introduction in 1914 of some receptacles having both configurations of slots and others having “T” slots.

Some countries have multiple voltages, frequencies and plug designs in use, which can create inconvenience and safety hazards. However, in Britain, there were recognizable two pin plugs and wall sockets appearing on the market as early as 1885. One of the two vertical prongs is slightly taller than the other, with a corresponding tall and short slot in the outlet, which makes it impossible to insert the plug backwards, ensuring that the “hot” and “neutral” connections cannot be reversed. As the need for safer installations became apparent, earthed three-contact systems were made mandatory in most industrial countries.