E.SAF Safety Circuit Fault in Mitsubishi FR-A800 Drive

E.SAF Safety Circuit Fault in the Mitsubishi FR-A800 Drive indicates that the drive has detected a fault in the Safety Stop (STO - Safe Torque Off) circuit. The FR-A800 continuously monitors the safety inputs to ensure that the safety circuit is functioning correctly. If the safety circuit becomes open, disconnected, or incorrectly configured, the inverter immediately disables its output and generates E.SAF to prevent unintended motor operation.

This fault generally indicates a problem with the Safety Stop wiring, safety relay module, STO input circuit, or safety switch configuration, rather than a fault in the motor or power section of the drive.

Possible Causes

• Safety circuit fault.
• Safety relay module failure.
• Fault in the external safety device.
• Open circuit between terminals S1 and SIC.
• Open circuit between terminals S2 and SIC.
• Incorrect Safety Stop (STO) wiring.
• Loose or damaged STO wiring.
• Shorting wire between S1 and PC disconnected when STO is not used.
• Shorting wire between S2 and PC disconnected when STO is not used.
• Manufacturer setting switches (SW3 and SW4) changed from their factory positions.
• Incorrect commissioning of the safety circuit.
• Faulty terminal connections.
• Internal safety input circuit fault.

Solutions

• Check the safety relay module for proper operation.
• Verify that the external safety circuit is functioning correctly.
• Inspect the wiring between terminals S1, S2, and SIC.
• Tighten any loose terminal connections.
• Repair or replace damaged safety wiring.
• When using the Safety Stop function, verify that the safety input source is operating correctly.
• Refer to the Safety Stop Function Instruction Manual for detailed troubleshooting.
• If the Safety Stop function is not used, install shorting wires between S1 and PC and between S2 and PC.
• Verify that manufacturer setting switches SW3 and SW4 are in their factory default (OFF) positions.
• Restore the switch settings if they have been changed.
• Restart the inverter after correcting the fault.
• Contact Mitsubishi technical support if the fault persists.

Additional Information

The Mitsubishi FR-A800 incorporates a Safe Torque Off (STO) function that removes torque-producing power from the motor without disconnecting the main power supply.

The drive continuously monitors the STO safety channels.

E.SAF is generated when:

• A safety circuit fault occurs.
• Either safety input channel becomes open.
• The STO wiring is incorrect.
• Required shorting links are missing when STO is not used.
• Manufacturer safety switch settings have been altered.

According to Mitsubishi:

• When using the Safety Stop function, terminals S1, S2, and SIC must be wired correctly through an approved safety relay module.
• When the Safety Stop function is not used, terminals S1–PC and S2–PC must remain shorted using the supplied shorting wires.
• Manufacturer setting switches SW3 and SW4 must remain in their factory default OFF positions.

Unlike an Emergency Stop, E.SAF specifically indicates that the drive's monitored safety circuit is invalid or incomplete, preventing the inverter from enabling motor output.

Common Symptoms

• Drive displays E.SAF Safety Circuit Fault.
• Motor cannot start.
• Inverter output is immediately disabled.
• Fault appears immediately after power-up.
• Fault occurs after modifying safety wiring.
• Fault appears after replacing the safety relay.
• Safety relay indicates an error.
• STO inputs remain inactive.
• Fault persists after reset until the safety circuit is restored.
• Drive operates normally after proper safety wiring is restored.

Recommended Troubleshooting Sequence

1. Switch OFF power to the inverter.
2. Verify whether the Safety Stop (STO) function is being used.
3. Inspect the safety relay module.
4. Check the wiring between S1, S2, and SIC.
5. Verify all terminal connections are secure.
6. Check for damaged or broken safety wiring.
7. If STO is not used, verify shorting wires are installed between S1–PC and S2–PC.
8. Inspect manufacturer setting switches SW3 and SW4.
9. Confirm both switches are in the factory default OFF position.
10. Restore correct wiring if necessary.
11. Restore power to the inverter.
12. Verify that E.SAF has cleared.
13. Test normal inverter operation.
14. Confirm proper operation of the external safety system.
15. Contact Mitsubishi technical support if the fault persists.

Safety Circuit Check Table

Check Point	Action
Safety relay module	Verify proper operation
STO wiring (S1, S2, SIC)	Check for correct wiring and continuity
Terminal connections	Tighten loose connections
Safety wiring	Inspect for damage or open circuits
S1–PC shorting wire	Verify installed if STO is not used
S2–PC shorting wire	Verify installed if STO is not used
SW3 switch	Confirm factory default OFF position
SW4 switch	Confirm factory default OFF position
Safety input source	Verify correct operation
Mitsubishi technical support	Contact if the fault remains after inspection

Preventive Maintenance Tips

• Inspect STO wiring during scheduled maintenance.
• Regularly test the safety relay module.
• Keep terminal connections clean and tight.
• Do not modify manufacturer safety switch settings unless instructed by Mitsubishi.
• Verify shorting links remain installed when the STO function is not used.
• Protect safety wiring from vibration and mechanical damage.
• Follow the Mitsubishi Safety Stop Function Manual during commissioning.
• Use only approved safety relays and safety components.
• Record any changes made to the safety circuit configuration.
• Record recurring E.SAF faults to assist long-term diagnostics.

Proper inspection of the Safety Stop (STO) circuit, safety relay module, S1, S2, SIC wiring, S1–PC and S2–PC shorting links, and manufacturer setting switches (SW3 and SW4), along with correct commissioning and routine maintenance of the safety system, will help prevent recurring E.SAF Safety Circuit Fault errors in Mitsubishi FR-A800 drives, ensuring reliable functional safety, dependable motor shutdown capability, and safe long-term operation of the drive system.