Cause: SAFE TORQUE OFF comes when the Safe Torque Off (STO) safety function has been activated. This function electronically inhibits the drive from producing torque, preventing the motor from rotating.

STO SAFE TORQUE OFF fault in Parker AC890 drive indicates indicates that the Safe Torque Off (STO) safety circuit is active, preventing the drive from enabling output to the motor. This is a safety feature, not an error — but if it appears unexpectedly or won’t clear, it needs to be addressed carefully.

Troubleshooting Steps:

• Check External Safety Circuits: Verify the status of all connected safety devices (e-stops, interlocks, etc.). Ensure they are in their normal operating (non-tripped) state.
• Inspect STO Wiring: Check for any signs of damage to the wiring.
• Verify STO Input Signals: Ensure the signals are consistent with the expected state for normal operation (STO inactive).
• Power Cycle the Drive: Turn off the power to the AC890 drive and wait a few minutes to allow any residual power to dissipate. Then, turn the power back on. This might clear a temporary fault.