Which logic element describes two or more normally closed switches in parallel?

• A. Nand
• B. Nor
• C. And
• D. Or

Answer: (A)

Think about how normally closed (NC) contacts behave and how parallel wiring changes the outcome. An NC switch is closed when its control input is not active and opens when the input is activated. If you have two NC switches in parallel, the current can flow as long as at least one of the switches is closed. That means the overall conduction condition is true whenever either input is false, i.e., (NOT A) OR (NOT B). This expression is equivalent to NOT (A AND B), which is the NAND function. So two NC switches in parallel implement the NAND logic.

The other options don’t match this behavior. AND would require both inputs to be true (both switches closed at the same time) for conduction, which isn’t what parallel NCs do. OR would imply conduction whenever either input is true in a different configuration, which also doesn’t align with how NC contacts in parallel respond to the inputs.