Competency and practice field guide
Normally-closed E-stop curriculum scenario: practice plan
Direct answer
The learner can create a truth table for healthy and actuated states, give stop priority and prevent an automatic run request after reset or power return.
Written for pLC beginners learning why de-energize-to-stop signals are interpreted separately from ordinary run commands.
Scope
Healthy contact state, actuated state, input electrical meaning, program tag meaning, stop priority, run request, output command and restart permission.
Signal path
Emergency-stop device through normally-closed path and input image into control logic, final output owner and modeled machine state.
Baseline practice
Healthy state allowing a separate deliberate start, actuation removing the request and release alone not restarting the machine.
Edge cases
Broken conductor, inverted tag, stuck input, start and stop together, reset held, latched run state, controller restart and power return.
Fault practice
A device, conductor, input, tag meaning, priority, latch, final-writer, output or restart mismatch.
Transfer to the job
The lesson retained as logic evidence while the real safety function is risk-assessed, engineered and validated independently.
Why use a normally closed E-stop input in a PLC lesson?
It teaches de-energize-to-stop interpretation: a healthy circuit holds a signal, while actuation or some open-circuit faults remove it. That lesson is not safety validation.
Should releasing an emergency stop restart a machine?
No. Release should make a controlled reset and deliberate restart possible only when all other requirements are satisfied.