Liebert Static Transfer Switch 2, Installation, Operation & Maintenance Manual, Page: 122 / 150

110 Specifications
15.2.4 Access
The STS2 is designed so all repairs and maintenance can be done from the front or top of the unit.
All components that may need repair or replacement during routine field maintenance are safely
accessed with the units in bypass without removing power from the unit. These components
include:
• All electronic PCB assemblies
• Power supply assemblies
• All fuses
• All circuit breaker plug-in modules
• Fans
• SCRs
All power connections are designed to maintain proper connection torque over the lifetime of the
unit without any maintenance. The integrity of the connections can be checked via infrared scan-
ning safely from the front or top of the unit.
All other components including power cables and connections, circuit breaker bases, etc. are
replaceable from the front or top of the unit only, but this requires all power to be removed from the
unit for safety. Although routine re-torquing of the power connections is not required, if mainte-
nance of these connections is needed, complete removal of power is required from the unit for
safety reasons.
15.2.5 Circuit Breakers
The STS2 is equipped with five molded-case, plug-in, non-automatic circuit breakers. The breakers
are UL listed for use up to 600 VAC and CE marked. The plug-in feature of the breaker includes an
interlock, which prevents the breaker from being unplugged without being in the OFF (open) posi-
tion.
Mechanical interlocks are provided on the breakers to prevent improper maintenance bypassing of
the solid-state switch. A bypass breaker cannot be closed unless the solid-state switch is connected
to the same input source and only one bypass breaker can be closed at a time. All breakers are
equipped with N.O. and N.C. auxiliary switches for monitoring of the breaker positions. The two
input breakers for the solid-state switching devices also are equipped with 48 VDC shunt trips to
allow for control by the STS2 logic. See the Circuit Breaker Schedule in
Figure 20 on page 38.
15.2.6 Cable Entrance
Removable conduit termination plates are provided in the top and bottom of the STS2 for termina-
tion of the two source input conduits or raceways and/or the output conduits or raceways.
15.2.7 Doors
A removable key lock hinged front door provides access to the circuit breakers.
!
WARNING
LETHAL VOLTAGES EXIST INSIDE THE UNIT DURING
NORMAL OPERATION. ONLY QUALIFIED SERVICE
PERSONNEL SHOULD PERFORM MAINTENANCE ON THE
STATIC SWITCH.
THE UNIT IS SUPPLIED BY MORE THAN ONE POWER SOURCE.
THE UNIT CONTAINS HAZARDOUS VOLTAGES IF ANY OF THE
INPUT SOURCES IS ON, EVEN WHEN THE UNIT IS IN BYPASS.
TO ISOLATE THE UNIT, TURN OFF AND LOCK OUT ALL INPUT
POWER SOURCES.
VERIFY THAT ALL INPUT POWER SOURCES ARE DE-
ENERGIZED AND LOCKED OUT BEFORE MAKING
CONNECTIONS INSIDE UNIT.