How to Troubleshoot ABB ACS580 Fault 5091 Safe Torque Off (STO)?
Getting the ABB ACS580 Fault 5091? This fault indicates that the Safe Torque Off (STO) circuit is active or broken. Learn how to check your safety wiring and restore drive operation. The Safe Torque Off (STO) function is a critical safety feature of the ABB ACS580 . It is designed to disable the control voltage to the power semiconductors of the drive output, effectively preventing the motor from generating torque. If your drive displays Fault 5091 , it means the drive has detected that the STO circuit is "open"—meaning the safety signal has been interrupted. When the STO circuit is broken, the drive cannot output power to the motor, regardless of any "Start" commands it receives. This is not just a fault; it is a safety state. Common Causes of Fault 5091 Open Safety Circuit: An emergency stop button or a safety gate switch in your machine's safety loop has been triggered. Loose Connections at XSTO: The physical connector on the dri...