NAND logic uses ___ switch contacts for connection to programmable controller input terminals.

NAND logic uses ___ switch contacts for connection to programmable controller input terminals.

• A. Normally-Open parallel
• B. Normally-Closed parallel
• C. Normally-Open series
• D. Normally-Closed parallel

Answer: (D)

In ladder logic, wiring determines the logic function: series contacts implement AND, while parallel contacts implement OR. A normally closed contact inverts the input state (closed when the input is off, open when the input is on). To realize NAND, you want the output to be energized unless all inputs are true. By using normally closed contacts for each input and wiring them in parallel, any one input being false provides a closed path through its branch to energize the output. If both inputs are true, all normally closed contacts open, removing all paths and leaving the output de-energized. So the configuration that produces NAND behavior is normally closed contacts in parallel.

In ladder logic, wiring determines the logic function: series contacts implement AND, while parallel contacts implement OR. A normally closed contact inverts the input state (closed when the input is off, open when the input is on).

To realize NAND, you want the output to be energized unless all inputs are true. By using normally closed contacts for each input and wiring them in parallel, any one input being false provides a closed path through its branch to energize the output. If both inputs are true, all normally closed contacts open, removing all paths and leaving the output de-energized. So the configuration that produces NAND behavior is normally closed contacts in parallel.