On a 4-wire delta-connected system, which conductor or busbar must be durably marked in orange?

In a 4-wire delta-connected system, the requirement to mark conductors or busbars is guided by safety practices to help identify their function and the voltage levels they carry. The conductor that must be durably marked in orange is the one associated with the highest phase voltage. This marking convention is in place to alert workers and maintenance personnel to the potential risks associated with higher voltage levels.

The marked conductor typically indicates a different level of safety precautions is needed when working with that specific connection. By marking the highest phase voltage conductor in orange, it provides a clear visual cue that helps mitigate the risk of accidental contact, thereby enhancing safety in environments where high voltages are present.

In contrast, the other options don't align with the NEC requirements regarding marking conductors in a 4-wire delta system. The grounded conductor, for instance, is usually identified with a different marking, and marking all conductors would dilute the critical information provided by the orange color. Additionally, marking the lowest phase voltage does not address the primary concern related to voltage risks. Therefore, the emphasis on the highest phase voltage conductor for the orange marking is crucial for safety compliance and awareness in electrical installations.