Industrial Engineer · phase 14 of 16
STO
Safe Torque Off, a certified drive safety function that prevents torque-producing energy without serving as electrical isolation.
The Explain card
- Plain English
- Safe torque off is a certified safety input on the drive that removes the gate signals from the IGBTs. With STO active the drive cannot make torque, whatever the control board is told.
- Example
- The emergency stop circuit opens the two STO inputs on the drive. The motor coasts, the drive reports it, and no contactor was needed to guarantee the motor could not be driven.
- Why it matters
- STO lets a drive be part of a safety circuit without a contactor in the motor leads, which is cheaper and more reliable. It is safe torque, and nothing more, so the motor terminals can still be live and a hoist still needs a brake.
- Hook
- The drive is disarmed, and the wires are still hot.
Where it sits in the deck
Phase 14: VFD Safety, Faults, and Diagnostics
What a drive does when it trips, what the fault codes are telling you, and how safe torque off stops the motor without killing the panel.
