There is no standard for this voltage!! In 2002 the IEC put forward the new voltage standard and change was as the 220v was charge to 230v, 380v was charge to 400v and 660v was charge to 690v all with the tolerance of +/- 10% the frequency is always based on 50Hz. You will find that each voltage has the square root of 3 as a multiplication (1.73). The reason is star Connection at 400v give you delta in 690v!
For achieving the correct 60Hz voltage (This is not a standard but correct mathematically and physically) Divider 60Hz/50Hz = 1.2. If you then wanted the correct 60Hz voltage multiplication for example 400v x 1.2, you get 480v at 60Hz! Since all Electrical motors, transformer, breaker etc in low voltage has and is producer for Max 690v +/- 10% the only way (which is not approved) is to take the tolerance 690v x1.1= 759v + 0% and - 20%! But the problem is that no approved institute will make up a certification on this because you are on absolute Max voltage nominal voltage limit!