The key word is "nominal"! A word used to describe something that is lower than the actual value of the said thing! From Wiki:So how can we use NEMA standard motors? The nameplates are required to be marked 230 volts for use on a nominal 240 volt system, and 460 for use on a nominal 480 volt system.
nom·i·nal (/ˈnämən(ə)l/), adjective - (of a price or amount of money) very small; far below the real value or cost.