STS FAULT ABB — STS Transfer Failure
At a glance
- Severity
- FAULT STOP
- Domain
- TRANSFER_SWITCH_SYSTEM
- Reference standard
- IEC 60947-6-1
What it means
The STS fails to transfer the load between the two UPS chains: losing one chain directly hits the load served by the affected branch.
Probable causes
- SCR or gate driver failure
- Source quality sensing in anomaly
- Overload at the moment of transfer
- Logic left in manual after maintenance
Where to start
Verify both inputs (voltage, phase, frequency) and the STS mode (auto/manual), plus board alarms.
Full guided diagnosis in the app
The diagnostic tree for this fault has 3 guided steps with measurements, checks and resolutions. You'll find it in DataCIQ, one of the five IndexOS apps: free, works offline.
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The same fault on other brands
More ABB codes
- FEED MISMATCH — Wrong A/B Feed Assignment
- JOINT OVERHEAT — Busway / Tap-off Overheat
- TRANSFER FAULT — ATS Transfer Failure
- 2310 — Overcurrent Fault
- 2330 — Ground Fault
- 3210 — DC Bus Overvoltage Fault
- 3220 — DC Bus Undervoltage Fault
- 4310 — Drive Overtemperature Fault