In a basic ladder logic representation, what is the function of a contact associated with a coil?

• A. The coil is energized when its associated contact(s) are closed (for NO) or open (for NC) in the rung, enabling the coil to energize.
• B. The coil energizes only when all contacts are open.
• C. The coil energizes regardless of contact state.
• D. The coil is energized only if the rung has a timer.

Answer: (A)

In ladder logic, a coil only energizes when the rung evaluates to true, meaning there is a complete path from power to the coil through the associated contacts. The contact acts as the gate for that path. A normally open contact must close to complete the circuit and energize the coil; a normally closed contact is closed when its controlling input is not active (and thus can also complete the path), but it opens when the input activates, breaking the path and de-energizing the coil. So the coil energizes when its associated NO contact is closed or when its associated NC contact is in its closed (non-actuated) state, enabling the rung to carry current to the coil. The other options don’t describe how a rung becomes true: energizing the coil only happens when the path is complete, not when all contacts are open, not regardless of state, and not only when a timer is involved.