In ladder logic, a normally open (NO) contact represents a condition that is closed when its input is true; how does it affect the coil?

• A. It is closed when its input is false, energizing the coil.
• B. It is open when its input is true, energizing the coil.
• C. It is closed only when its input is true, and when closed it energizes the coil.
• D. It is closed regardless of input, energizing the coil.

Answer: (C)

A normally open contact behaves like a switch that is open until its controlling input becomes true. When that input is true, the contact closes and provides a path from power to the coil, allowing current to energize it. If the input is false, the contact stays open and the coil does not energize. So the coil is energized exactly when the input is true and the NO contact is closed. In broader circuits, NO contacts in series require all inputs to be true to energize (AND behavior), while NO contacts arranged in parallel offer alternative paths (OR behavior).