Which statement best describes the relationship between relay schematics and ladder logic program symbols?

• A. Both use the same symbols
• B. Ladder logic uses PLC instruction symbols; Relay schematic uses electrical symbols
• C. Ladder logic uses electrical symbols; Relay schematic uses PLC instruction symbols
• D. Neither uses symbols

Answer: (B)

The main distinction is that ladder logic uses PLC instruction symbols, while relay schematics use electrical symbols. Ladder logic is a programming way to represent control logic for a PLC, so its symbols (like a contact representing an input condition or a coil representing an output) are symbolic of programming instructions. Relay schematics, on the other hand, depict actual electrical hardware with standard electrical symbols for coils, contacts, power sources, and wiring. So the two domains use different symbol sets, even though they can be related conceptually (a PLC input in ladder can correspond to a relay contact, and a PLC output to a relay coil). The other options misstate which symbols belong to each domain.