All references are based on the 2017 edition of the NEC, unless otherwise noted.
Each of the conductors shown in the Photo could be used as a grounded conductor in accordance with Sec. 200.6(A). Perhaps the white wire could be used for the neutral of a 120/240V system while the white wire with the red tracer used as the grounded conductor of a corner-grounded delta system.
The Code does not specify which method of identification must be used for any particular voltage class or system type. It’s the installer’s choice. In fact, if conductors for these systems are kept in raceways and enclosures, separate from the other systems, the installer could choose to use only one of these identification methods for any and all grounded conductors. For example, white insulation could be used for all grounded conductors. However, if any of the grounded conductors from other systems are installed in the same raceway or enclosure, using only one color such as the white would be a violation of Sec. 200.6(D).
But what if all the voltages are the same? For instance, what if there are several 208Y/120V panels being powered from different transformers installed in the electric room, with the 120V branch circuits from one panel installed in the same wireway with 120V branch circuits from the other panels? In this case, would each grounded conductor in the wireway need to be identified differently than the grounded conductors coming from the other panels?
The literal wording in Sec. 200.6(D) appears to require the grounded branch-circuit conductors coming from each 208Y/120V panel to be identified differently than the other grounded conductors in the same wireway. The voltage and type of systems may all be the same, but these circuits are, in fact, being fed from different separately derived systems. Using white insulation to identify each grounded conductor in this case literally would be a violation of Sec. 200.6(D) because it states “different systems” rather than “different types of systems” or “different nominal voltage systems” in the way Sec. 210.5(C)(1) does for ungrounded conductors. Application of the rule in this way may not be the intent, but there are many other types of “systems” throughout the Code, including optional standby, legally required, energy storage, and energy management, among others, that may need to comply with Sec. 200.6(D) as well.
It would be best to have a conversation your authority having jurisdiction (AHJ) about how to properly identify any grounded conductors.
