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In other words, are there any historical reasons that set mains supply voltage to 120, 127, 220, 240Vrms per phase, and 50/60Hz? These are the most common voltages/frequencies, there are many others, depending on country. Here in Brazil a single phase is always 127Vrms/60Hz.

PDuarte
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  • Great! But what about the voltages? – PDuarte Feb 29 '16 at 21:39
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    Compromise between industrial users (motors) and the emerging private consumer user market (lighting). Everything about our electrical grid is based around those two loads - the first commercial products of the electrical industry. The earliest distribution networks were only for industrial customers so you have oddities like 25hz – crasic Feb 29 '16 at 21:44
  • Nominal voltage in brasil is depending on the area 110, 115, 127,130, 220 or 240V, you are living in one of the most diverse countries that exist ;) Though the vast majority there runs on 127/220, anyways for the voltage there exists this question: http://electronics.stackexchange.com/questions/204033/ – PlasmaHH Feb 29 '16 at 21:49
  • @PlasmaHH Tks, wow all these variations here? I suppose I don't know my country this well :). Still, this link it's not very convincing, nobody seems to know exactly why... – PDuarte Feb 29 '16 at 22:07
  • @PDuarte: I don't think you get any more information than that. In the beginning someone arbitrarily chose a value. Then survival of the fittest. I don't see what there is more to know behind that – PlasmaHH Feb 29 '16 at 22:13

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