Which statement describes the NOT function in ladder logic?

• A. It inverts the logic state using a normally open contact
• B. It doubles the energization path using parallel contacts
• C. It inverts the logic state using a normally closed contact
• D. It uses two coils in series

Answer: (C)

In ladder logic, inversion is accomplished with a normally closed contact. A normally closed (NC) contact conducts when its input is not energized and opens when the input is energized. That means the rung will energize the output when the controlling input is false, and stop energizing when the input is true, which is exactly how a NOT operation behaves.

If you used a normally open contact, the rung would energize only when the input is true, not invert it. Parallel (or multiple) paths would create alternative ways to energize the output (an OR effect), not invert the input. Using two coils in series changes how outputs respond and isn’t about reversing the logic of a single input.