Final answer:
The white insulated conductor may be used as an ungrounded circuit conductor when it is properly re-identified using tape in visible or accessible locations for 480-volt duct heaters or as a traveler in a 4-way switch circuit.
Step-by-step explanation:
The conductor with white insulation, traditionally known as the neutral wire, is generally used as the return path for electric current in AC wiring. However, by certain codes and practices, it may be repurposed as an ungrounded circuit conductor under specific conditions. Two of the included scenarios are acceptable with proper identification: (II) when marked with black tape if used to connect a 480-volt duct heater; and (III) if marked with pink tape when used as a traveler for a 4-way switch. The markings must be where the wire is visible or accessible. In both instances, re-identifying the white wire is a critical safety practice to avoid confusion and potential electrical hazards. The first scenario (I), using it to connect 12-volt luminaires, is not mentioned in typical codes for conductor re-identification and thus wasn't addressed.