If the standard motor is rated for 60Hz/480V, then I see a problem running it at 50Hz/480V.
Not my problem if the motor cannot take it. Supposedly Siemens has been consulted and they may have blessed using the motor this way, although I am not privy to what they said and how it was phrased, or even what was actually asked, and it is not known to me just how this was handled.
It is a Siemens motor with three different ratings on the nameplate. I have seen the motor up close and personal and can verify the nameplate does actually say all this stuff.
one rating says 400V/275A/50Hz IE3
another says 480/60Hz/225A MC1
and the third says 480V/60Hz/275A IE3
It also says NEMA MG12-12 SF1.15 60Hz on another line. I think it also says TENV somewhere but that part is cut off in the picture I have and I can only see the "TE" part.
most of this is consistent with the motor datasheet that came from Siemens although there is additional information on the datasheet and some of what is on the nameplate is not in the datasheet.
at this point my plan is to tell our customer it is not a violation of the NEC or any other standard I can think of to run the motor this way. the actual motor side of it is just not in my scope.