Safe torque off

What does A5A0 mean?

The Safe Torque Off (STO) function is active, meaning the safety circuit signal(s) connected to the STO connector have been lost or removed. Depending on parameter 31.22, this can be a warning when STO is intentionally activated, or an indication of an unintended safety circuit issue. The drive will prevent motor rotation for safety.

• One or both STO input signals (e.g., STO_IN1, STO_IN2) are momentarily interrupted or lost from the safety controller (PLC, safety relay).
• Incorrect parameter setting (e.g., P31.22 STO fault reaction) configured to issue a warning instead of a trip for a single channel loss.
• External safety relay contacts opening intermittently due to vibration or faulty wiring.
• Loose wiring connection at the drive's STO terminal block (e.g., X1, X2 terminals).
• Fault in the external safety circuit causing one channel to drop out while the other remains active.

Click steps to track your progress.

1. 1

   Verify the status of both STO input signals (e.g., STO_IN1, STO_IN2) from the safety controller (PLC or safety relay outputs) using a multimeter.

2. 2

   Inspect and re-torque all wiring connections at the drive's STO terminal block (e.g., terminals X1, X2 for STO inputs).

3. 3

   Check parameter P31.22 (STO fault reaction) to confirm it is set to "Warning" (e.g., value 1) for single channel loss if desired.

4. 4

   Measure voltage across STO input terminals (e.g., X1-common, X2-common) to confirm stable 24VDC signals from the safety circuit.

5. 5

   Review the external safety circuit for intermittent contact behavior or short duration signal drops from the safety relay or PLC.