In ladder diagrams for an NCTO set of contacts, which symbol is typically used?

In ladder diagrams, the symbol used for a set of normally closed contacts is very specific, reflecting the action of the device in the circuit. For an NCTO (Normally Closed, Normally Open) configuration, the symbol that denotes normally closed contacts is represented as "IV." This designation visually communicates to those interpreting the diagram that the contacts will be closed in their resting state (unenergized) and will open when activated, which is essential for understanding the operation of safety circuits or control sequences.

The choice of "IV" aligns with standard conventions in electrical schematics, ensuring clarity and uniformity across different diagrams. This consistency allows electricians and engineers to quickly understand the function of each component in a circuit without needing extensive context. In contrast, other symbols may represent different configurations, such as normally open contacts or other electrical states, which would not accurately represent the NCTO operation required in this case. Thus, the selection of "IV" is critical for ensuring the proper function and safety of the systems designed using these ladder diagrams.