Tesla starts AC
Early in the history or electricity, Thomas Edison's General Electric company was distributing direct current (DC) electricity at 110 volts in the United States. Then Nikola Telsa the devised a system of three-phase alternating current (AC) electricity at 240 volts. Three-phase meant that three alternating currents slightly out of phase were combined in order to even out the great variations in voltage occurring in AC electricity. He had calculated that 60 cycles per second (60Hz) was the most effective frequency. Tesla later compromised to reduce the voltage to 110V for safety reasons.
Europe goes to 50Hz
With the backing of the Westinghouse Company, Tesla's AC system became the standard in the United States. Meanwhile, the German company AEG started generating electricity and became a virtual monopoly in Europe. They decided to use 50Hz instead of 60Hz to better fit their metric standards, but they kept the voltage at 110V.
Unfortunately, 50Hz AC has greater losses and is not as efficient as 60HZ. Due to the slower speed 50Hz electrical generators are 20% less effective than 60Hz generators. Electrical transmission at 50Hz is about 10-15% less efficient. 50Hz transformers require larger windings and 50Hz electric motors are less efficient than those meant to run at 60Hz. They are more costly to make to handle the electrical losses and the extra heat generated at the lower frequency.
Europe goes to 220V
Europe stayed at 110V AC until the 1950s, just after World War II. They then switched over to 220V for better efficiency in electrical transmission. Great Britain not only switched to 220V, but they also changed from 60Hz to 50Hz to follow the European lead. Since not that many people had electrical appliances in Europe at that time, the change-over was not that expensive for them.
U.S. stays at 110V, 60Hz
The United States also considered converting to 220V for home use but felt it would be too costly, due to all the 110V electrical appliances people had. A compromise was made in the U.S. in that 220V would come into the house where it would be split to 110V to power most appliances. Certain household appliances such as an electric stove and electric clothes dryer would be powered at 220V.