Scott35,
Although you could install all Black ungrounded conductors on any of these systems - such as a job with 480Y/277 3ph 4 wire and 208Y/120 3ph 4 wire - and still be in compliance with the NEC,...
If both of these systems are in the same building and you are using multiwire branch circuits, then 210-4(d) requires that each ungrounded conductor be identified as to phase and voltage. The method of identification is left to the designer/installer but must be posted at each branch-circuit panelboard in the building. This requirement only applies to multiwire branch circuits and does not require the use of special identification of the grounded conductors. 200-6(d) would require that where both grounded conductors are in the same raceway, junction box, ect that the first grounded conductor be white or natural gray and the second grounded conductor be white with a colored stripe other than green.
