And Applications By John W Webb.pdf =link= | Programmable Logic Controllers Principles

John W. Webb Typical Editions: 3rd, 4th, 5th (published by Prentice Hall) Target Audience: Engineering students, technicians, automation trainees, PLC programmers

"Note that the Stop pushbutton is drawn as a normally closed (NC) symbol in the ladder diagram. However, in the PLC input module, the physical Stop button should be wired NC. Why? For failsafe operation. If the wire breaks to the Stop button, the PLC sees an open circuit and stops the motor immediately. If you wired it NO, a broken wire would make the Stop button useless." John W