Safe torque off

What does 5091 mean?

The Safe Torque Off (STO) function has been activated, meaning the motor's torque production is safely disabled. This usually results from a break in the external safety circuit connected to the XSTO connector or a diagnostic fault setting, preventing the motor from starting or running.

• External safety circuit open (e.g., emergency stop button pressed, safety gate open, light curtain tripped).
• Faulty wiring in the STO safety chain (e.g., broken wire to XSTO1 or XSTO2 terminals, loose connections).
• Failure of an external safety relay or safety PLC providing the STO signal to the drive.
• Incorrect or missing voltage applied to the STO input terminals (e.g., 24VDC not present on XSTO1 and XSTO2).
• Internal failure of the drive's STO circuit, though this is rare and usually indicates a hardware defect.

Click steps to track your progress.

1. 1

   Verify the status of all external safety devices (e.g., E-stop buttons, safety gates, light curtains) in the safety circuit.

2. 2

   Measure the voltage across STO input terminals (e.g., XSTO1 and XSTO-COM, XSTO2 and XSTO-COM); it should be 24VDC when STO is inactive.

3. 3

   Check continuity of all wiring from the external safety relay/PLC to the drive's STO input terminals (e.g., XSTO).

4. 4

   Reset any tripped safety relays or clear safety PLC faults in the external safety system.

5. 5

   If voltage is present and wiring is confirmed good, test the drive's internal STO functionality by momentarily removing and re-applying a valid STO signal.