- Industrial machinery
- Variable frequency drives
5091
ABB ACS880 5091: Safe torque off is active
Risk level
Critical
Stop using the equipment and contact a professional.
Urgency
Immediate
Quick answer
Fault 5091 means both Safe torque off inputs are inactive under the documented ACS880 indication setting. A running drive stops and cannot restart until both STO signals are restored and faults are reset.
Safety first
What to do now
- Keep the machine stopped and record the complete indication
Do not issue another start command. Record drive model firmware fault 5091 any accompanying FA81 or FA82 message and which machine safety device or event preceded the stop.
- Verify only normal operator safety devices
A trained operator may confirm from the normal operating position that guards emergency stops and other safety devices are in their intended state. Escalate before resetting when the reason for the STO demand is unknown.
What you must never do
- Do not attempt this professional task: Validate both STO channels and the machine safety function
What a technician must be able to justify
A technician is coming
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Validate both STO channels and the machine safety function
What they doA qualified ABB drive and machine-safety technician should follow the exact ACS880 hardware and firmware manuals to test the dual-channel STO circuit wiring safety controller drive inputs and parameter 31.22 behaviour before authorising reset and restart.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Industrial machinery
- Brand
- ABB
- Product type
- Variable frequency drives
Known code variants
- ABB 5091
- ABB ACS880 fault 5091
- ABB Safe torque off 5091
What it means
The message identifies a safety-input state rather than a failed drive component. Loss of one STO channel produces separate FA81 or FA82 faults and requires qualified safety-circuit diagnosis.
Warnings and stop conditions
- Criticalsource verified
Do not bypass Safe torque off or reset 5091 until the cause of the safety demand is understood. Only qualified personnel may open the drive cabinet test STO wiring or return the machine to service.
Evidence: ABB ACS880 primary control program firmware manual
Sources and technical references
- 1
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