Vertiv™ | Liebert® STS2/PDU
™
User Manual | Rev. 6 | 10/2017 78
To manually select the preferred source:
1. Close the input breakers CB6, CB7, CB1 and CB2.
2. Select SOURCE XFERS from the menu bar.
The Select Preferred Source screen is displayed in the Event Display.
3. Check the Mimic to verify that Source 1 and Source 2 input voltages are correct.
4. Select SOURCE 1 or SOURCE 2 as your preferred source.
This source is now monitored as the preferred source throughout the various configurations set up through the
touchscreen.
5. Verify that the correct source is designated as the preferred source and that the input source changes to the desired
source.
The Mimic is updated to indicate the new preferred source. The source is now highlighted with blue and that
source is labeled as the preferred source. If the Transfer Inhibit message is displayed, check for alarm messages
on the Active Status window. Correct alarm conditions before attempting a source transfer.
10.3 Enabling Remote Source Selection
If your system is equipped with the optional Remote Source Selection option, it must be enabled.
From the Color Graphical Display:
1. Select CONFIG from the menu bar.
2. Select SYSTEM SETTINGS from the Configuration menu.
3. Select SYSTEM OPTIONS from the System Settings menu.
4. Select YES for the REMOTE SOURCE SELECT choice.
10.4 Maintenance Bypass
The Liebert STS2/PDU is equipped with two key-interlocked, bypass breakers, CB4 and CB5, to allow manual
bypass of the switch electronics for either input source in the event of switch failure or for maintenance of the
switch. Refer to Figure 3. While operating on maintenance bypass, all voltages are removed from the static
transfer switch electronics to facilitate safe repair, without de-energizing the load using a make-before-break
switching sequence.
However, the unit can be bypassed using a make-before-break switching sequence only to the same source to
which that the switch is connected, as indicated by the highlighted static transfer switch box on the Mimic
screen.
In the event of source or switch failure, the unit should be bypassed only to the current input source. For
convenience, instructions for the bypass procedure can be displayed on the touchscreen by selecting the BYP.
PROC option from the menu bar.
The Mimic is used to verify the status of the unit during the bypass procedures. In the unlikely event that the
Color Graphical Display is not available, open the front door and look through the slots in the control door. If you
can see green LEDs on the gate driver board through that slot, then the unit is connected to the source
referenced on the label below that slot. See Figure 60.
NOTE
The preferred source may also be changed via the optional Remote Source Selection option, thereby initiating a
transfer remotely
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