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Most countries in the world have standardised their electricity supply systems to one of two frequencies: 50 hertz or 60 hertz. The list of 60 hertz countries, most of them in the New World, is shorter, but this is not to say that 60 hertz is less common. The 60 hertz countries are: American Samoa, Antigua and Barbuda, Aruba, Bahamas, Belize, Bermuda, Canada, Cayman Islands, Colombia, Costa Rica, Cuba, Dominican Republic, El Salvador, French Polynesia, Guam, Guatemala, Guyana, Haiti, Honduras, South Korea, Liberia, Marshall Islands, Mexico, Micronesia, Montserrat, Nicaragua, Northern Mariana Islands, Palau, Panama, Peru, Philippines, Puerto Rico, Saint Kitts and Nevis, Suriname, Taiwan, Trinidad and Tobago, Turks and Caicos Islands, United States, Venezuela, Virgin Islands (U.S.), Wake Island.[1] (
http://www.philip.allen.org/voltages.htm)
The following countries have a mixture of 50 Hz and 60 Hz supplies: Bahrain, Brazil (mostly 60 Hz), Japan (60 Hz used in western prefectures).[2] (
http://www.50hz.com/pwchrt2.htm)
Most countries have chosen their television standard to match their mains supply frequency.
It is generally accepted that Nikola Tesla chose 60 hertz as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60hz to the 1 2 5 10 structure popular with metric standards.
Other frequencies were somewhat common in industrial use in the first half of the 20th century, and remain in use in isolated cases today. 25 Hz power, much of it generated at Niagara Falls, was used in Ontario and the northern USA. Some 25 Hz generators were in use at Niagara Falls up until the mid-1990's, for large industrial customers who did not want to replace existing equipment. The lower frequency eases the design of low speed electric motors, especially commutator-type motors for electric traction applications such as railways, but causes a noticeable flicker in incandescent lighting.
Off-shore, textile industry, marine,computer mainframe, aircraft and spacecraft applications sometimes use 400Hz, for technical benefits of reduced weight of apparatus or higher motor speeds.
16.67 Hz power is still used in some European rail systems, such as in Sweden.
It should be noted that AC-powered appliances can give off a characteristic hum at the multiples of the frequencies of AC power that they use.