20-750-2262C-2R — 755 Series Safe Torque Off Option Card, SIL 2 / PLd

The 20-750-2262C-2R is a Safe Torque Off (STO) option card for the 755 series AC drive. It installs into one of the drive's option card slots and adds hardwired safety inputs that, when de-energized, inhibit the drive's gate pulses and prevent the motor from generating torque — without requiring the controller to issue a stop command. The STO function is rated SIL 2 (IEC 62061) and PLd Category 3 (ISO 13849-1), making it a certified safety component for machine safety architectures.

Most AC drives in industrial automation can be stopped by removing the run command from the control system. That works for normal operation, but it doesn't meet the requirements of a certified safety function — the control system itself could be the source of a hazardous condition, or communication could be disrupted. The 20-750-2262C-2R takes the safety path hardware, removing the dependency on the control system for the safety stop. As long as the STO inputs are de-energized, the motor cannot be made to produce torque regardless of what the drive's software is doing.

Specifications

Parameter	Value
Part Number	20-750-2262C-2R
Compatible Drive	755 Series AC Drive
Safety Function	Safe Torque Off (STO)
Safety Rating	SIL 2 (IEC 62061), PLd Category 3 (ISO 13849-1)
STO Input Channels	2 (dual-channel, independently monitored)
STO Input Voltage	24V DC
STO Input Current	~6 mA per channel
Response Time (STO activation)	≤ 8 ms
Feedback Output	STO status relay (NC contact)
Discrepancy Time	Configurable (monitors channel disagreement)
Installation	Drive option card slot
Operating Temperature	−10°C to 60°C
Standards	IEC 62061 (SIL 2), ISO 13849-1 (PLd Cat 3), CE, UL

Wiring the STO Circuit

The two STO input channels connect to the output contacts of a safety relay or the solid-state safety outputs of a safety PLC. Both channels must be energized (24V DC) for the drive to operate normally. De-energizing either or both channels activates STO.

Use individually shielded cable for the STO input wiring, separate from the drive's power wiring. Safety circuit wiring routed alongside high-voltage cables picks up induced noise that can cause nuisance STO trips.
Keep the cable run short — typically under 30 m. Longer runs increase the cable capacitance that the safety circuit must charge and discharge on each operation, potentially affecting response time.
The STO feedback relay (normally closed) opens when STO is active. Wire this contact back to the safety controller for monitoring — it confirms the STO state has been achieved and allows the safety controller to detect if the STO card has failed to respond.
Do not connect the STO inputs directly to the same 24V supply as the drive's control I/O without going through the safety relay contacts. The purpose of the safety relay is to provide the monitored, force-guided contact opening that makes the circuit certifiable.

Validation and Safety System Integration

Installing the 20-750-2262C-2R is only the first step. A safety function must be validated as a complete system — the safety relay (or safety PLC output), the wiring, the STO card, and the feedback monitoring — before the machine can claim compliance with the rated SIL 2 / PLd level. Validation involves testing the complete safety function under normal and fault conditions:

Verify STO activates correctly when the safety relay de-energizes (E-stop pressed).
Verify the STO feedback relay contact opens and is detected by the monitoring circuit.
Verify that resetting the safety relay re-energizes the STO inputs and that the drive does not automatically restart — the restart must require a deliberate operator command.
Test the discrepancy fault: with the drive running, interrupt one STO channel only and confirm the card reports a fault within the configured discrepancy time.
Document all validation tests in the machine's safety file.

FAQ

Q: Does STO stop the motor immediately?

STO removes the gate drive — the motor coasts to a stop under its own inertia and the load's inertia. It does not actively brake the motor. For applications where coasting creates a hazard (e.g., a large flywheel that takes minutes to coast to rest), a mechanical brake or a safe stop sequence (SS1) that decelerates the motor before STO engages is needed.

Q: Can the drive be running at full speed when STO is activated?

Yes. STO activates regardless of operating speed. The motor will coast from whatever speed it was running. The application's risk assessment must determine whether this coasting behavior is acceptable for the specific hazard being guarded against.

Q: Does activating STO generate a drive fault that requires acknowledgment?

STO activation sets a status indication in the drive, but whether it generates a latching fault requiring reset depends on the card's configuration. In most safety applications, STO should latch — the drive should not restart automatically when the STO inputs are re-energized. Configure the restart behavior to require an explicit operator or controller restart command.

Q: Can the 20-750-2262C-2R be used without a safety PLC — just a safety relay?

Yes. A conventional safety relay (E-stop relay, Category 3 or 4) with force-guided contacts connected to the STO inputs is a valid implementation. The STO card itself provides the SIL 2 / PLd-rated safety function; the safety relay provides the monitored input contact that starts the signal chain.

Q: Which option card slot does this card install into on the 755 drive?

The 20-750-2262C-2R installs into a designated safety option slot on the 755 drive. The 755 series has multiple option card slots with specific slot assignments — the safety card must go in the correct slot for the STO function to operate. Consult the 755 drive's option card installation instructions for the slot assignment for your specific drive frame size.

20-750-2262C-2R 24V DC IO Option Module New Factory Sealed 207502262C2R