Vertiv Liebert STS2/PDU - Maintenance Bypass

Vertiv™ | Liebert
®
STS2
™
100-1000A, 50/60Hz User Manual | Rev. 12 | 11/2017 103
14.2.3 Maintenance Bypass
The Liebert STS2 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 the static transfer switch one-line diagram (Figure 2). While operating on maintenance bypass, all
voltages are removed from the Liebert STS2 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.
In the event of source or switch failure, the unit should be bypassed only to the current input source.
The LED display is used to verify the status of the unit during the bypass procedures. In the unlikely event that
the LED display is not available, open the front door and look through the slots in the control door. If you can see
green LED’s 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 43.
Bypass Procedures for Source 1
To bypass the switch for Source 1:
1. Verify that Source 1 is supplying power via the LED display.
• If the LED Display is not available, check the gate driver board LED’s through the slots in the control panel. See
Figure 43.
2. Remove the interlock key from CB5 and place it in the CB4 interlock.
3. Open the alternate source input breaker CB2.
Verify that CB2 LED is Off.
4. Rotate and remove the CB2 interlock key.
5. Insert the key in the CB4 bypass breaker interlock.
6. Rotate the interlock keys in the CB4 bypass breaker interlock to retract the interlock.
7. Close bypass breaker CB4.
Verify that CB4 LED is On.
8. Open source input breaker CB1.
Verify that CB1 LED is Off.
9. Rotate the CB1 interlock key and remove it to lock out the breaker.
10. Secure the key according to your site’s lockout/tagout procedure.
11. Open output breakers CB3 and CB3A (if supplied) to remove power and isolate the static switch from the load.
Verify that CB3 and CB3A LED’s (if supplied) are Off.
12. Verify that the output LED is On.
Power is now flowing directly from the source to the load, without passing through the static transfer switch.
NOTE
To bypass the Source 1 static transfer switch when Source 2 is presently active, you must first transfer to Source
1. See 14.2.2 - Manual Transfer / Preferred Source Selection.