Emerson Static Transfer Switch User Manual

When an alarm is triggered, a red LED is lit in the control panel. A pair of buttons allows you to turn 

off the horn and reset the alarm.

An optional key lockout switch for the Liebert STS2 enables or disables all push button inputs, except 

for the alarm silence button. The key lockout switch is mounted on the front of the unit. See 

Figures 8 to 10 for the key lockout switch location on each unit.

• To disable the buttons, turn the key to the top of the switch, toward the closed padlock icon.
• To enable all of the buttons, except the alarm silence, turn the key to the horizontal position, 

toward the open padlock icon.

This section discusses the system turn-on, shut-down and bypass procedures for LED-based Liebert 

STS2. 
If your unit has an LCD touch screen, see10.0 - Operating Instructions for the Touch Screen 

Interface for instructions these procedures.

This section provides instructions to turn on your Liebert STS2. The LEDs provide the basic informa-

tion required to ensure proper operation. To monitor metering data, use a PC terminal.
1. Ensure that all Liebert STS2 breakers—CB1, CB2, CB3A (if supplied), CB3, CB4, and CB5—are 

in the OFF (open) position.
a. Ensure that the key interlocks for CB1 and CB2 have their bolts retracted. 
b. Ensure that the key interlocks for CB4 and CB5 have their bolts extended, thus preventing 

CB4 or CB5 from being turned ON. 

c. Ensure that the circuit breakers respective LEDs are off.

2. Source/input power should be applied to both Liebert STS2 inputs. 

Check that the green LEDs for each source are lit. 

3. Verify that nominal input voltages are applied to both inputs (Source 1 and Source 2). 

Check that the green LEDs monitoring the sources are lit indicating the sources are within 

acceptable tolerances.

4. Close CB1.

The green LED monitoring CB1 turns on.

NOTE
If your Liebert STS2 is connected to a PDU with a Wye configuration, enable the Wye Output 

Refer to 12.1 - Using the RS-232 Port for instructions. 

NOTE
For redundant output switch units, CB3 descriptions apply to CB3 and CB3A.