What is the correct statement about normally open and normally closed contacts in safety interlocks?

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Multiple Choice

What is the correct statement about normally open and normally closed contacts in safety interlocks?

Normally closed contacts are closed when the control circuit is not energized and open when it is energized. In safety interlocks, this behavior means that if power is removed or the interlock is actuated, the NC contact opens and the safety circuit is interrupted, stopping the equipment. This fail-safe behavior is what makes NC contacts useful in safety circuits: the default state keeps the circuit complete, and any intentional actuation or loss of power breaks the circuit to ensure a safe stop. The statement described is the correct one because it accurately captures that NC contacts are closed in the de-energized state and open when energized. The other ideas aren’t correct: NO contacts are not closed in a de-energized state (they are open and close only when energized), NO contacts are not always closed, and NC contacts are indeed used in safety applications.

Normally closed contacts are closed when the control circuit is not energized and open when it is energized. In safety interlocks, this behavior means that if power is removed or the interlock is actuated, the NC contact opens and the safety circuit is interrupted, stopping the equipment. This fail-safe behavior is what makes NC contacts useful in safety circuits: the default state keeps the circuit complete, and any intentional actuation or loss of power breaks the circuit to ensure a safe stop.

The statement described is the correct one because it accurately captures that NC contacts are closed in the de-energized state and open when energized. The other ideas aren’t correct: NO contacts are not closed in a de-energized state (they are open and close only when energized), NO contacts are not always closed, and NC contacts are indeed used in safety applications.

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