Define normally open and normally closed contacts and how they change state.

Define normally open and normally closed contacts and how they change state.

• A. Normally open contacts are closed when the coil is energized and open when de-energized; normally closed contacts are closed when de-energized and open when energized.
• B. Normally open contacts are open when the coil is de-energized and close when energized; normally closed contacts are closed when de-energized and open when energized.
• C. Normally open contacts are always closed; normally closed contacts are always open.
• D. Normally open contacts depend on coil temperature; normally closed depend on coil humidity.

Answer: (B)

In relay and switch terminology, contacts change state based on whether the control coil is powered. A normally open contact is open when the coil is de-energized and closes when the coil is energized, allowing current to flow only after activation. A normally closed contact is closed when the coil is de-energized and opens when the coil is energized, stopping current when activated. So, with no power to the coil, the NO path conducts nothing while the NC path conducts; applying power flips both states—NO closes and NC opens. This behavior is used to design circuits that respond to a control signal and to create predictable fail-safe or interlocking behavior.

In relay and switch terminology, contacts change state based on whether the control coil is powered. A normally open contact is open when the coil is de-energized and closes when the coil is energized, allowing current to flow only after activation. A normally closed contact is closed when the coil is de-energized and opens when the coil is energized, stopping current when activated.

So, with no power to the coil, the NO path conducts nothing while the NC path conducts; applying power flips both states—NO closes and NC opens. This behavior is used to design circuits that respond to a control signal and to create predictable fail-safe or interlocking behavior.