How would you interpret a simple relay-logic rung on a ladder diagram?

How would you interpret a simple relay-logic rung on a ladder diagram?

• A. Power flows from the source through the coil and contacts on the rung; the state of the output depends on the status of those contacts.
• B. Power flows only through the lamp.
• C. The rung shows only a single switch with no coil.
• D. The rung has no influence on the output.

Answer: (A)

In ladder logic, a rung is a single circuit path that can energize an output device such as a relay coil. Power flows from the left-side supply through the devices drawn on the rung—the input contacts in series—and reaches the output coil on the right. The coil energizes only if all required contacts are in the conducting state, so the rung is complete. If any required contact is not conducting, the path is open and the coil remains de-energized, so the output stays off. Normally-open contacts close when their control coil is energized, while normally-closed contacts open when energized; this determines how the rung behaves under different conditions. So the correct interpretation is that power flows from the source through the coil and the necessary contacts on the rung, and the output state depends on the status of those contacts.

In ladder logic, a rung is a single circuit path that can energize an output device such as a relay coil. Power flows from the left-side supply through the devices drawn on the rung—the input contacts in series—and reaches the output coil on the right. The coil energizes only if all required contacts are in the conducting state, so the rung is complete. If any required contact is not conducting, the path is open and the coil remains de-energized, so the output stays off. Normally-open contacts close when their control coil is energized, while normally-closed contacts open when energized; this determines how the rung behaves under different conditions. So the correct interpretation is that power flows from the source through the coil and the necessary contacts on the rung, and the output state depends on the status of those contacts.