What you'll learn
**Reported symptom:** The guard is closed and the safety relay resets, but the VFD remains in STO active / inhibit.
Lab time: ~14 minutes.
Lesson briefing
VFD STO Channel 1 Open
Reported symptom: The guard is closed and the safety relay resets, but the VFD remains in STO active / inhibit.
The circuit was commissioned from a known-good drawing. Treat every terminal as suspect, but test from source to load instead of guessing. Use voltage mode on an energised control circuit and continuity only after the simulated circuit is isolated.
Your task
Compare both safety output channels at the relay and at the VFD STO inputs.
Choose the fault category only when the measurements support it.
Hints
Confirm the normal run command separately; it cannot override active STO.
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This lesson uses 9 placed components on the lab canvas. Components are vendor-neutral (no proprietary trademarks); the wiring rules apply to any equivalent industrial part.
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