Just read 417.3 . Puts my mind at rest.If it is bare wires, separated by air. then assuming it is in good condition, I cant see an issue unless it could come in to contact with something.
have a look at 417.3
have a think, have you identified a risk or a deviation from the regs.
or is it just something you have not seen before and are thinking it must be wrong because it is unusual?