Describe a ladder logic diagram and its main components.

• A. A ladder-style schematic of control circuits; components include normally open/closed contacts, coils, timers, and relays.
• B. A power distribution single-line diagram with bus bars only.
• C. A mechanical schematic for valve actuators.
• D. A wiring diagram for a three-phase motor.

Answer: (A)

Ladder logic diagrams are a ladder-style way to depict control circuits used in programmable logic controllers. They show two vertical rails representing power and return, with horizontal rungs that carry logic from left to right. Each rung uses input devices shown as normally open or normally closed contacts, which model sensors or switches, and an output device shown as a coil that energizes to drive an actuator. Timers and relays appear as function blocks within the rungs, adding timing control and isolation or latching behavior. A rung can place multiple contacts in series to require all conditions or in parallel to provide alternative paths, giving AND and OR logic in a visually intuitive form. This representation focuses on control logic for machines and processes, not on power distribution diagrams, mechanical schematics for valve actuators, or wiring diagrams for motors.