A safe torque off (STO) system for an AC motor is disclosed that can enable STO using any or a combination of a software control and a hardware control, wherein the software control is provided by a digital logic module and the hardware control by a driver supply regulator. Proposed system provides for redundancy of signals to trigger the STO and implements various safe categories of STO using same hardware. It decelerates the motor slowly so as to avoid stress on electrical and mechanical components. The motor stops rotating when the proposed system triggers an STO so that non-electrical maintenance work can be done without switching off the complete drive. The STO system proposed also prevents an unexpected start during such works. The system has a human machine interface for its operation.
