Since 1949 (see ANSI C84.1-1989), the nominal system voltages in the US are: 120V, 208V, 240V, 480V, and 600V. There are +/- tolerances for these voltages, but they are on a utility by utility basis.
The NEC says "... The actual voltage at which a system operates can vary from the nominal within a range that permits satisfactory operation of the equipment."
Motor manufacturers have decided to rate their devices at utilization voltages of 110V, 200V, 230V, 460V, 575V. Some end use appliance manufacturers rate their equipment at maximum voltages such as 125V.
[This message has been edited by JBD (edited 01-02-2002).]
