In a numerical cross-reference system, which type of contacts are underlined?

In a numerical cross-reference system, normally closed contacts are underlined to indicate their function and specific characteristics within the system. Normally closed contacts are those that are closed when not energized, allowing current to flow through them in their default state. Underlining these contacts helps differentiate them visually from other types of contacts, such as normally open contacts, which are open when not energized and only allow current flow when activated.

This visual distinction is important for anyone reading the schematics or working with the system, as it quickly conveys crucial information about the state and behavior of the contacts in various conditions. By recognizing which contacts are underlined, individuals can ensure they interpret wiring diagrams and implement control logic accurately, improving troubleshooting and system reliability.