In a parallel arrangement of two NC limit switches controlling two cylinders, the logic produced is ______.

• A. AND
• B. OR
• C. NOR
• D. NAND

Answer: (D)

In a parallel arrangement of normally closed (NC) limit switches, the path for current exists as long as at least one switch is not actuated. An NC switch is closed when its mechanism isn’t pushed, and it opens when actuated. When you wire two NC switches in parallel, the circuit remains complete unless both switches are actuated (both open). Only then is the path broken. That behavior—output is high unless both inputs are active—matches the NAND function: the output is false only when both inputs are true.

So, this configuration embodies the NAND logic: it conducts unless both switches are actuated. If the switches were in series, the behavior would resemble NOR (output true only when neither input is active), which helps see why parallel NC gives NAND rather than the other options.