What is required for identifying ungrounded system conductors in a building with multiple nominal voltage systems?

In a building that has multiple nominal voltage systems, it is crucial to ensure that ungrounded system conductors are easily identifiable to promote safety and prevent errors during maintenance or modification. The requirement that they must be permanently posted at each branch-circuit panelboard provides clear, accessible information about the system's conductors right at the point where the distribution occurs.

Having this information permanently displayed helps electricians and maintenance personnel quickly understand the configuration of the electrical system, including nominal voltages and phases, thus improving safety by reducing the risk of incorrect connections or maintenance actions.

While other methods such as labeling with colors, tagging, or using phase tape can assist in identifying conductors, they may not provide the permanent and universally recognized standard that posting at the branch-circuit panelboard does. Such postings are typically aligned with NEC requirements for clarity and reliability in identifying electrical components within a complex system.