European countries use 50Hz They decided to use 50Hz instead of 60Hz, because they use a decimal (US using duodecimal) , this calculation is more convenient, but they still retained the voltage of 110V. Unfortunately, 50Hz AC efficiency is far poorer than 60Hz.
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Frequency Standardization As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). Standardization allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids.
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