Answer / aamirali

USA use above for safety & economical reasons. Observe synchronous speed (Ns=120f/P)and output power in watts (P=1.732VI). so, you can design your equipment with less power rating & also less rpm for rotating machines as compared to 50hz, 220ac v. Saving the cost & minimize the electrical accidents.

Answer / raja.n

because current is inversly prportional to the frequency.
so it reduces the conductor dia meter as well as
tranmission cost

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