Smart UPS - 'Mains input bad' Event Messages after switching 3‑Phase input Source
Issue
The UPS logs the following events:
- UPS: Main input bad. (0x01B0)
- UPS: Main input bad cleared. (0x01B1)
- UPS: Main input bad. (0x01B0)
- UPS: Main input bad cleared. (0x01B1)
- UPS: On battery power due to frequency and phase difference. (0x010)
These events typically occur when switching from a 3‑phase primary input source to a 3‑phase secondary source, such as a generator, or when switching back from the secondary source to the primary.
Both sources are accepted by the UPS when it is started on either one individually, and no issues occur when the input is changed to single‑phase.
Product Line
SRT8KRMXLI, SRT10KRMXLI
Environment
3 phase input with a secondary source
Resolution
This issue can arise when the phase order is different between the two input sources. At the start-up, the UPS will accept any phase sequence. But during the switchover, it's looking for the same sequence as previously receiving.