What Should I Check If an SLF1 Fault Occurs on an Altivar 71/61 Drive?
Resolution:
An SLF1 fault indicates a Modbus communication timeout. This means communication between the drive and the controller was previously working, but no data was received within the configured timeout period ([Modbus timeout] (ttO)).
Checks to Perform
1. Configuration Checks
- Verify the controller (server) status is running correctly (not stopped or in error).
- Ensure the network is not overloaded with excessive traffic.
- Check the Modbus timeout (ttO) setting—consider increasing it if necessary.
- Confirm the time interval between Modbus requests is shorter than the timeout value.
2. Installation and Environment Checks
- Use the recommended shielded twisted-pair Modbus cable (e.g., TSXCSA100, TSXCSA200, TSXCSA500).
- Maintain at least 30 cm (12 in.) separation between Modbus and power cables to reduce interference.
- If cables must cross, ensure they cross at 90 degrees.
- Install termination resistors at both ends of the RS485 network to prevent signal reflections.
- Properly connect cable shielding to protective ground (earth) when possible.
Recommendation
Carefully review both communication settings and physical wiring. Most SLF1 faults are caused by incorrect timing parameters, poor cable installation, or electrical noise.
If this article does not answer your question, check out our FAQ database that has answers to more commonly asked questions:
Frequently Asked Questions - Schneider Electric (se.com)
If this FAQ did not solve your issue, you can call us at 1-888-778-2733 Option 2 and then 4 or e-mail us atdrive.products.support@se.comto create a case with our Technical Support Team.
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