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

AND 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 series

Answer: (C)

AND logic requires both conditions to be true to energize the PLC input. To achieve that with switch contacts, you wire normally-open contacts in series. A normally-open contact closes only when its switch is actuated, so the current path to the PLC input exists only if both switches are activated. This gives the required condition: both inputs must be true for the PLC to register a signal. If you used normally-open contacts in parallel, any one of them closing would energize the input (OR behavior), which isn’t AND. Using normally-closed contacts would invert or complicate the logic, not straightforwardly provide an AND condition.

AND logic requires both conditions to be true to energize the PLC input. To achieve that with switch contacts, you wire normally-open contacts in series. A normally-open contact closes only when its switch is actuated, so the current path to the PLC input exists only if both switches are activated. This gives the required condition: both inputs must be true for the PLC to register a signal. If you used normally-open contacts in parallel, any one of them closing would energize the input (OR behavior), which isn’t AND. Using normally-closed contacts would invert or complicate the logic, not straightforwardly provide an AND condition.