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2.6.4 Automatic Retransfers to UPS
The following critical bus conditions must be present to initiate an automatic retransfer of the critical
load from the bypass source to the UPS inverter:
1. Critical load was initially transferred to the bypass source due to a system overload only. A
manual retransfer from bypass is required if the transfer to bypass was caused by any condition
other than output overload.
2. Overload has since dropped below 95% of the rated load.
3. Both the Input and the DC source (MBD) circuit breakers have remained closed since the
overload transfer.
4. OK to Transfer signal received from the control logic for at least 10 seconds, within 5 minutes of
the system overload transfer. A manual retransfer from bypass is required for overloads lasting 5
minutes or more.
5. Cyclic-type overloads, which occur up to five (select range is 0 to 5) times in 60 minutes, are
automatically returned to the inverter for each event including the Nth overload.
NOTE
If you do not want the UPS system to initiate any automatic retransfers, this can be set during
the initial commissioning or by calling your local Liebert Services representative.