In electrical control circuits, what does a normally closed contact do?

• A. It conducts current only when energized.
• B. It never conducts current.
• C. It conducts current regardless of input.
• D. It conducts current when its input is not energized; it opens when energized.

Answer: (D)

A normally closed contact conducts current by default and opens when the control input is energized. In other words, in its resting state there is continuity, and energizing the coil (or actuator) breaks that continuity. This matches the idea that it conducts current when its input is not energized and opens when energized. This default-on behavior is why such contacts are used for safety interlocks and stop circuits—for example, a stop button wired as normally closed will allow current to flow until the button is pressed (energizing or actuating it), at which point the contact opens and the circuit is interrupted. In contrast, a normally open contact would conduct only when energized, and the other two descriptions describe states that don’t apply to a normally closed contact.