Vertiv™ | Liebert
®
STS2
™
100-1000A, 50/60Hz User Manual | Rev. 12 | 11/2017 102
8. Close Output Breaker CB3 (and CB3A in a redundant output configuration).
9. Verify that CB3 LED is lit, indicating that CB3 is closed and the output and load are energized.
• In a redundant output configuration, verify the CB3A LED is lit, indicating that CB3A is closed and the output and load
are energized
10. Press the Reset and Silence buttons simultaneously to reset any previous alarms.
11. Verify that no red or yellow (amber) LED’s are lit indicating an active alarm, transfer is inhibited or a bypass circuit breaker
is closed.
If the alarm LED remains lit, check the PC terminal to identify the alarm. Refer to 11.0 - Alarm and Faults for a description
of the alarms and possible causes. All active alarm conditions should be corrected before proceeding.
12. If the unit is supplied with an output distribution cabinet, close output breakers as required.
13. Turn On the load equipment following the load equipment manufacturer’s recommendations.
14.2.2 Manual Transfer / Preferred Source Selection
The preferred source buttons allow you to change the preferred source. Transfers are only permitted when the
voltage and current are within their proper operating range and the sources are synchronized. Transfer is inhibited
if the deviation exceeds the parameter set in the Source Set Points.
To manually select the preferred source:
1. Ensure that the Transfer Inhibit (NOXF) LED is not lit.
If the Transfer Inhibit LED is lit:
• Check to see whether the red alarm LED is lit.
• If the alarm LED is lit, check the alarm messages on a PC terminal.
• Correct alarm conditions before attempting a source transfer.
2. Verify that the LED’s are lit for both sources, indicating power is present and within acceptable tolerances.
3. Verify that the LED’s for the SCRs (Liebert STS1 and Liebert STS2) are lit.
4. Verify that the input breakers CB1 and CB2 are closed.
• Verify that their respective LED’s are lit.
5. Push the Preferred Source button for the desired source. See Table 12 on page 100.
The Preferred Source (LED_PREFx) LED turns On for that source.
When conditions are correct, the switch transfers the load to the alternate source by selecting the alternate source as the
preferred source.
This source is now monitored as the preferred source throughout the various configurations set up through the PC
terminal.
6. Check the LED’s to verify that the correct source is designated as the preferred source and that the input source changes
to the desired source and the output (OUT) LED remains lit.
NOTE
If one source will be de-energized for an extended period (hours or days), set the unit to bypass mode for the
remaining source. Without using bypass, if a failure occurs in the switch components for remaining source, the
Liebert STS2 does not have a second source to switch to and the load would not receive power. See 14.2.3 -
Maintenance Bypass on page 103 for bypass instructions.
NOTE
When the remote source selection option (Remote Control) is activated, a change of state (Remote Preferred
Source Selection) may initiate a transfer if the appropriate contacts are closed.
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