What are the two standard states of ladder diagram contacts indicating whether circuits are closed?

• A. Normally Open and Normally Closed
• B. Open-Loop and Closed-Loop
• C. Active and Inactive
• D. Rigid and Flexible

Answer: (A)

Two standard states of ladder diagram contacts are normally open and normally closed. These describe how a contact behaves with its controlling input and whether the path conducts before any input changes. A normally open contact does not conduct until the controlling input is energized, at which moment it closes and completes the circuit. A normally closed contact conducts when the input is not energized and opens when the input energizes, interrupting the circuit. This distinction lets you design logic where a path can be made to close only under an active condition (using normally open) or rely on a safe default that remains closed until a signal changes (using normally closed). For example, a start pushbutton is typically normally open—the circuit closes to run the machine when pressed—while a safety interlock might be normally closed to keep the circuit complete unless a fault occurs.