What is the function of a normally closed auxiliary contact in a control circuit when the associated device is energized?

• A. It opens on energization to provide interlock or feedback, helping ensure correct sequencing.
• B. It closes on energization to enable operation.
• C. It remains closed when de-energized.
• D. It has no effect on circuit behavior.

Answer: (A)

Normally closed auxiliary contacts are wired into control circuits to create interlocks and provide feedback for sequencing. When the device they’re attached to is not energized, the contact stays closed, allowing current to flow through its leg. Once the device energizes, the auxiliary contact opens, breaking that path. This opening on energization is what gives you interlock or feedback signals—it's how the circuit prevents another action from occurring too early or verifies that a device has started. In practice, this behavior helps ensure the correct order of operations and safe, coordinated control.

The other ideas don’t fit this function. A normally closed contact does not close when energized—that describes a normally open behavior. Saying it remains closed when de-energized is true for the rest state, but it doesn’t explain its action when the device energizes. And saying it has no effect on circuit behavior ignores the deliberate interruption or signaling the closed-to-open transition provides.