Emerson Static Transfer Switch User Manual

The static transfer switch can be manually bypassed to allow the power from a source to directly flow 

to the output load. This bypass allows the unit’s electronics to be serviced without dangerous voltages 

being present.
The Liebert STS2 includes key-interlocked maintenance bypass breakers that allow either input 

source’s electronics to be bypassed for maintenance without interruption of power to the load. The 

maintenance bypass allows all electronics to be isolated from the input, output, and bypass connec-

tions. Bypass instructions are available from the touch screen and are discussed later in this manual.

The Liebert STS2 is equipped with an interface to configure and monitor the unit either locally or 

remotely. The Color Graphical Display is a touch screen LCD that provides a color diagram (Mimic) 

that displays the current status of the unit. System parameters are displayed and help is available to 

define events. See Figure 44 below and Figure 30. The touch screen menus allow the operator to ini-

tiate source transfers, view event and history logs, and view bypass and other operational instruc-

tions. 

Touch screen control buttons allow you to reset alarms, silence the audible alarm, review configura-

tions, event and history logs, preferred source, startup and bypass procedures, and the help menu. 

Qualified personnel, with a password, can use these menus to configure parameters, select a pre-

ferred source and do manual source transfers.
LED display units do not have the color LCD touch screen. Instead of the touch screen, these units are 

monitored by a series of LEDs and controlled by a series of push buttons.
Both units can be accessed from a terminal, or a PC running terminal emulation software, that is 

attached to the unit. Through the RS-232 access, you can monitor and configure the unit, plus 

remotely select a preferred source. See 12.1 - Using the RS-232 Port on page 76 for instructions on 

using the RS-232 interface.