In ladder logic, what does a normally open contact indicate?

• A. It remains open regardless of input signal.
• B. It is closed and conducts current when the input signal is present, completing the rung.
• C. It indicates a fault in the input signal.
• D. It acts as a fuse in the circuit.

Answer: (B)

In ladder logic, a normally open contact acts like a switch that is open by default and will close when its input signal is active. When the input is present, the contact closes, allowing current to flow through the rung and complete the path to energize the output or move to the next rung. If the input isn’t active, the contact stays open and the rung won’t energize. This behavior is what lets you design logic that only triggers when a sensor or button is true. It isn’t indicating a fault, nor does it function as a fuse, and it doesn’t stay open regardless of input.