Technical Specifications

FAQ

1. What is the main function of the 20-750-S Safe Torque Off module?

The 20-750-S provides a hardwired Safe Torque Off function for compatible PowerFlex 750-Series drives. When the safety circuit removes the required safety-enable condition, the module prevents the drive’s output power devices from switching in the pattern required to produce motor torque. This allows the drive to enter a defined torque-off safety state without requiring the main input power to be removed from the entire drive. The STO function is intended for integration into a properly designed machine safety system and should not be treated as a conventional start/stop control.

2. What safety ratings are supported by the 20-750-S?

The 20-750-S is specified for safety applications up to Category 3 and Performance Level e according to the applicable ISO 13849 requirements, and SIL CL3 according to IEC 61508 and IEC 62061. The module is also associated with IEC/EN 60204-1 and IEC 61800-5-2 requirements. The final safety performance of a machine does not depend on the option module alone. The complete safety system, including the safety controller, input devices, wiring, drive, motor, and application architecture, must be correctly selected, installed, validated, and maintained.

3. What power supply does the 20-750-S require?

The 20-750-S uses a customer-supplied 24 V DC safety power supply with a tolerance of ±10%. The safety power should be provided through an appropriate PELV or SELV supply suitable for the safety application. The module has separate safety-related connections, including SP+ / SP− for safety power and SE+ / SE− for the safety-enable circuit. Correct polarity, voltage level, grounding, wiring separation, and protection should be verified during installation because an incorrect supply or wiring configuration can prevent the safety function from operating correctly.

4. Can the 20-750-S be installed in any PowerFlex 750 drive option port?

The Safe Torque Off module can generally be installed in an available option port of the compatible PowerFlex 750-Series drive. However, there is an important exception for Integrated Motion applications: the 20-750-S must be installed in Port 6. The selected port should therefore be confirmed against the actual drive configuration and application requirements before installation. The module should be firmly seated in the option-port connector and the retaining screws tightened to the specified torque without overtightening.

5. What type of wiring is recommended for the 20-750-S safety terminals?

The safety terminals use multi-conductor shielded cable. The specified conductor range is 0.3–0.8 mm², corresponding approximately to 28–18 AWG, with a recommended strip length of 10 mm. Control and safety wiring should be routed carefully to minimize the possibility of electrical interference or accidental damage. In particular, safety-related control wiring should be properly separated from high-power wiring and installed according to the applicable electrical codes and machine safety design requirements.

6. What happens to the motor when the 20-750-S activates Safe Torque Off?

When the Safe Torque Off function is correctly activated, the drive prevents the output power devices from switching in the sequence required to generate motor torque. The purpose is therefore to remove the drive’s ability to actively produce torque rather than to provide a conventional controlled motor stop. Mechanical forces can still cause motor movement in certain applications, such as suspended loads, stored mechanical energy, or external forces acting on the motor shaft. Additional mechanical braking or other safety measures may therefore be necessary depending on the machine design.

7. Can the 20-750-S be used as the normal start/stop control for a PowerFlex drive?

No. Safe Torque Off is a safety function and should not be used as the normal operational start/stop command for the drive. Normal machine operation should use the appropriate drive control functions and control inputs. The 20-750-S should be incorporated into a safety circuit where removal of motor-producing torque is required as part of a machine safety strategy. Using the STO circuit for routine operational switching can result in inappropriate drive behavior and unnecessary safety-system cycling.

8. What should be checked if the 20-750-S does not operate correctly?

Troubleshooting should begin by verifying that the drive is safely isolated before any physical inspection is performed. Check the 24 V DC safety power supply, SP+ / SP− connections, SE+ / SE− safety-enable circuit, terminal wiring, cable condition, connector seating, and the installed option-port connection. The input voltage should be measured against the specified operating range, and the safety circuit should be checked for open circuits, incorrect polarity, or unintended voltage drops. If the wiring and supply are correct but the safety function or drive status remains abnormal, the drive’s diagnostic information and safety-related fault indications should be reviewed before replacing the module.