Vertiv Liebert STS2 User manual

SL-20610_REV12_09-21 1 Guide Specifications
Proprietary and Confidential © 2021 Vertiv Group Corp.
Vertiv™ Liebert® STS2
GUIDE SPECIFICATIONS
Automatic Static Transfer Switch
100A - 1000A
1.0 GENERAL
1.1 Summary
These specifications describe the requirements for an automatic static transfer switch. The Liebert®
STS2 is a solid-state, three-pole, dual-position transfer switch designed to switch automatically and
manually between two synchronized three-phase AC power sources.
The input power shall be supplied from two different AC power sources, which are nominally of the same
voltage level, phase rotation and frequency. The primary purpose of the Liebert® STS2 is to allow virtually
uninterrupted transfer from one source to the other in case of the failure of one source or by manual
initiation for test or maintenance. The switching action shall not connect together the two sources of
power that would allow backfeeding one source to the other. The Liebert® STS2 shall allow for either
source to be designated as the preferred source. The switch will automatically transfer to the preferred
source and remain so until manually initiated to transfer or until the selected source fails. The Liebert®
STS2 shall be furnished with key-interlocked static switch isolation and bypass Molded-Case Switches
(MCSs) to each source, which allow uninterrupted manual transfer to and from either source for
maintenance.
1.2 Standards
The specified system shall be designed, manufactured, tested and installed in accordance with:
•American National Standards Institute (ANSI)
•Canadian Standards Association (CSA)
•Institute of Electrical and Electronics Engineers (IEEE)
•ISO 9001
•National Electrical Code (NEC)
•National Electrical Manufacturers Association (NEMA)
•National Fire Protection Association (NFPA 70)
•Underwriters Laboratories (UL)
•EN 61000-6-4 & 6-2
The Liebert® STS2 shall be UL and UL listed per UL Standard 1008 for Automatic Transfer Switches or
1008S for Solid State Transfer Switches
The Liebert® STS2 shall comply with the latest FCC Part 15 EMI emission limits for Class A computing
devices and the emission limits of EN/IEC61000-6-4Class A.
The Liebert® STS2 shall safely withstand without misoperation or damage:
•Transient voltage surges on either AC power input as defined by ANSI/IEEE C62.41 for Category
B3 locations (high surge exposure industrial and commercial facilities)

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•Electrostatic discharges (ESD) up to 10 kV at any point on the exterior of the unit
•Electromagnetic fields from portable transmitters that are not within 3 ft. (1m) of the unit
The Vertiv™ Liebert® STS2 shall comply with the immunity requirements of EN/IEC61000-6-2 Class A.
1.3 Definitions
•STS - Static Transfer Switch
•SCR - Silicon Controlled Rectifier
•MTBF - Mean Time Between Failure is the actual arithmetic average time between failures of the
critical AC output bus.
•Molded-case Switches (MCS) - A circuit breaker that has no automatic thermal overload trip
element but does have a magnetic trip element for short-circuit/fault protection. Short-circuit
and overload protection must be provided by an upstream overcurrent device.
1.4 System Description
1.4.1 Design Requirements
1. Voltage. Input/output voltage specifications of the Liebert® STS2 shall be [(200) (208) (220) (240)
(380) (400) (415) (480) (575) (600) ] volts, three phase, (60) (50) Hz, (3)-wire plus ground.
2. Output Load Capacity. Specified output load capacity of the Liebert® STS2 shall be (100) (250) (400)
(600) (800) (1000) A. The Liebert® STS2 shall be continuous rated to carry a full 100% load.
1.4.2 Modes of Operation
The Static Transfer Switch shall be a three-pole, double-throw, solid-state, automatic transfer switch that
is fed from two AC power sources. One source shall be designated as the preferred source, while the
other is the alternate source. Selection of which input source is preferred shall be user selectable from
the operator control panel. All transfers shall be a fast break-before-make with no overlap in conduction
from one source to the other.
The Static Transfer Switch is fuseless and consists of six pairs of Silicon Controlled Rectifiers (SCRs)
connected in an AC switch configuration. The SCRs are continuous rated to carry 100% of the Liebert®
STS2 rated load while operating within the Liebert® STS2 specifications. The use of fuses for protection
is not permitted due to possible fuse clearing in an out of phase transfer.
The Static Transfer Switch logic power shall automatically power up when connected to the power
source. The control panel shall be active as long as one input to the Liebert® STS2 is energized. The
Liebert® STS2 shall be supplied with factory default settings; mechanical trim pots shall not be used for
calibration or adjusting settings. All settings must be adjustable; the settings shall be
adjusted/configured from the LCD display.
1. Normal Mode. The unit is fed by two sources with the output connected to the load. In normal
operation, the load shall be connected to the preferred source as long as all phases of the preferred
source are within the acceptable limits. The transfer voltage limits shall default to ±10% of the nominal
input voltage for steady state conditions, with low voltage transfer limits having an inverse time
relationship that is within the IEEE Std. 446 computer voltage tolerance envelope. Upon failure of the
preferred source, the load shall be transferred to the alternate source. After the preferred source
returns to within the acceptable voltage limits for at least the preset adjustable retransfer time delay
(typically 3 seconds) and is in phase with the alternate source, the load shall be retransferred
automatically to the preferred source. The automatic retransfer to the preferred source can be
disabled if so selected by the user from the operator control panel. Provided the preferred source is
qualified, in the event the alternate source fails, the Liebert® STS2 will always transfer to the preferred
source, regardless of the automatic retransfer setting.

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2. Load Current Inhibit (also called Ipeak or Peak Current Overload). The Liebert® STS2 shall sense
the load current and, if the load current exceeds an adjustable preset level deemed to represent a
load inrush or fault condition, the Liebert® STS2 shall disable the automatic transfer even if the
voltage on the selected source exceeds the transfer limits. The load current transfer inhibit shall be
user selectable between [(automatically) (manually)] reset after the current returns to normal to allow
for continued protection against a source failure.
3. Manual Transfer (Optimized Transfer Disabled). The Vertiv™ Liebert® STS2 shall allow manually
initiated transfers between the two sources, providing the alternate source has proper phase rotation
and is within acceptable voltage and frequency limits and phase tolerances with the preferred source.
Allowable phase differences between the sources for manually initiated transfers shall be adjustable
from the operator control panel. The Liebert® STS2 shall be capable of tolerating transfers up to 30
degrees out of phase for emergency conditions. The user-adjustable phase synchronization window
shall be limited to ±30 degrees. If the transfer is manually initiated, the Liebert® STS2 shall transfer
between the two sources without interruption of power to the load greater than 1/8 cycle or less
provided that both sources are available and synchronized within the user-adjustable phase
synchronization window. For sources where the two frequencies are not exactly the same (as would
be the case between a utility and standby generator source), manually initiated transfers shall be
delayed by the Liebert® STS2 until the two sources are within the user-adjustable phase
synchronization window.
4. Manual Transfer (Optimized Transfer Enabled). The Liebert® STS2 shall allow manually initiated
transfers between the two sources, providing the alternate source has proper phase rotation and is
within acceptable frequency limits, is within acceptable voltage and frequency limits at any phase
angle difference. When a manual transfer is initiated, the Liebert® STS2 will perform an optimized
transfer such that the flux linkage is balanced when transferring between sources. The transfer time
is typically less than one line-cycle and the load voltage is maintained within the ITIC voltage
classification.
5. Emergency Transfer (Optimized Transfer Disabled). In an effort to maintain power to the load, upon
loss of the source that the load is connected to, the Liebert® STS2 shall automatically transfer to the
other source within ¼ cycle typical, (depending on the load, phase difference between sources, and
type of source failure) overriding any retransfer time delays or other inhibits except load overcurrent
providing that the other source is available.
6. Emergency Transfer (Optimized Transfer Enabled). The Liebert® STS2 shall perform an optimized
transfer such that the flux linkage is balanced when transferring between sources, when any source
anomaly that exceeds certain voltage thresholds is detected. The transfer time is typically less than
one line-cycle and the load voltage is maintained within the ITIC voltage classification. By balancing
the flux linkage, the Liebert® STS2 minimizes any saturation current should a downstream
transformer be connected.
7. SCR Failure. The Liebert® STS2 shall continuously monitor the status of the SCR switching devices
for proper operation. In the event of a shorted SCR on the source powering the load, the Liebert®
STS2 shall automatically alarm the condition and trip open the other source isolation MCS. In the
event of a shorted SCR on the other source, the Liebert® STS2 shall automatically alarm the condition
and trip open the other source isolation MCS. In the event of an open SCR, the switch shall
automatically alarm the condition and transfer to the other source. All open and shorted SCR alarm
conditions shall be latched and require the system to be repaired and reset to restore normal
operation.

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8. System Bypass. The Liebert® STS2 shall be furnished with key-interlocked maintenance bypass
MCSs that allow the Liebert® STS2 power, controls and monitoring electronics to be bypassed to
either input source for maintenance without interruption of power to the load. The packaging of the
Liebert® STS2 shall have all electronics isolated from the input, output and bypass connections to
allow servicing of any components without access to hazardous voltages when the unit is in
maintenance bypass.
9. Rotational/Regenerative Loads.When a rotational load, such as a motor, is connected to the output
of the unit, the time to detect a source fail and ultimately transfer to the alternate source can extend
beyond the previously outlined timeframe. Regardless, the critical bus voltage is always maintained
within the ITIC standard. Recommend contacting Vertiv for guidance if connecting to a
rotational/regenerative load to the Liebert® STS2.
1.4.3 Performance Requirements
1. Nominal Input/Output Voltage: [(200) (208) (220) (240) (380) (400) (415) (480) (575) (600)] volts
three phase, [(3)]-wire-plus-ground, 4-wire-plus-ground for non-US
2. Default Voltage Range: +10%, -10% of nominal
3. Nominal Frequency: (50) (60) Hz
4. Maximum Continuous Current: [(100) (250) (400) (600) (800) (1000)] amps
5. Source Voltage Distortion: Up to 10% THD with notches and ringing transients
6. Surge Protection: Sustains input surges without damage per criteria listed in ANSI C62.41 Category
B3
7. Sensing and Transfer Time: Refer to Modes of Operation section (Page 2-3) for details.
8. Overload Capability:
•125% for 30 minutes (100-400A), 125% for 10 minutes (600-1000A)
•150% for 2 minutes
•500% for 0.25 seconds
9. Short Circuit Withstand Capability:
208-240V
380-480V
600V
100-250A
125kA
100kA
50kA
400-600A
100kA
100kA
25kA
800A
1000A
125kA
100kA
65kA
65kA
25kA
25kA
1.4.4 Environmental Conditions
1. Storage Temperature Range: -20° to +70°C (-4° to 158°F)
2. Operating Temperature Range: 0° to 40°C (32° to 104°F)
3. Relative Humidity: 0 to 95% without condensation
4. Operating Altitude: Up to 4000 ft. (1200m) above sea level without derating. Above 4000 ft. (1200m),
output current is derated by 6% per 1000 ft. (18% per 1000m).
5. Storage/Transport Altitude: Up to 40,000 ft. (12,200m) above sea level
6. Audible Noise: Less than 55 dBA at 5 ft. (1.5m) with audible alarm off

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1.4.5 Reliability
MTBF
The Vertiv™ Liebert® STS2 shall be designed for high reliability and high availability with an MTBF
exceeding 1,000,000 hours. To the fullest extent practical, redundant circuits and components shall be
used to eliminate single points of failure.
Power Supply
Redundant power supplies shall be provided to prevent any single-point power supply failure mode. The
Liebert® STS2 shall have two completely separate power supplies mounted on separate boards so a
power supply can be replaced while the load is on bypass. There shall be two separate DC buses, one
from each power supply, to provide redundancy throughout the controls.
Logic
Control logic shall be triple-redundant. Each of the three logic modules shall have its own separate power
connection to each power supply bus. Each logic module shall be fused to prevent it from shorting the
power supplies if an internal failure occurs. Gating and control logic shall be partitioned so that the failure
of one source’s gating or sensing logic does not prevent the switch from transferring to the other source.
Components
All electrical components requiring normal maintenance or repair shall be replaceable without de-
energizing the load, assuming that at least one source is available. Solid-state switching devices shall be
packaged to allow safe repair of the switching devices without having to de-energize the load. All MCSs
shall be of a plug-in or draw-out type to allow replacement without de-energizing the load. All control
and logic components shall be mounted separate from the power components.
Fuseless
No fuses are used to protect the solid-state power switching devices.
Access
The Vertiv™ Liebert® STS2 shall be designed for front access only. The Liebert® STS2 shall be designed
so all installation, repairs and maintenance can be done from the front or top of the unit. The Liebert®
STS2 shall be designed to minimize the exposure of hazardous voltages to allow safe servicing of the
unit while the load is energized. Barriers shall be used on and around customer connections to protect
personnel during maintenance.
1.5 Documentation
1.5.1 Equipment Manual
The manufacturer shall furnish an installation, operation and maintenance manual with installation,
startup, operation and maintenance instructions for the specified system.
1.5.2 Proposal Submittals
Submittals with the proposal shall include:
•A system one-line diagram.
•Outline drawing including weights, dimensions, heat dissipation and recommended service
clearances.
•Location and detailed layouts of customer power and control connections.
•Description of equipment to be furnished, including deviations from these specifications.

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1.5.3 Delivery Submittal
Submittals upon STS delivery shall include a complete set of submittal drawings and one (1) installation,
operation and maintenance manual that shall include a functional description of the equipment with block
diagrams, safety precautions, instructions, step-by-step operating procedures and routine maintenance
guidelines, including illustrations.
1.5.4 Spare Parts
A list of recommended spare parts shall be furnished upon request.
1.6 Warranty
The manufacturer shall provide a warranty against defects in material and workmanship for 12 months
after initial system startup or 18 months after ship date, whichever occurs first. (Refer to the Warranty
Statement for details.)
1.7 Quality Assurance
1.7.1 Manufacturer Qualifications
A minimum of five years’ experience in the design, manufacture and testing of STS systems is required.
The specified system shall be completely factory-tested before shipment. Testing shall include, but shall
not be limited to: quality control checks, Hi-Pot test (two times rated voltage plus 1000 volts, per UL
requirements), transfer tests and metering calibration tests. The system shall be designed, manufactured
and tested according to world-class quality standards. The manufacturer shall be ISO 9001 certified.
1.7.2 Factory Testing
Before shipment, the manufacturer shall fully and completely test the Vertiv™ Liebert® STS2 to assure
compliance with the specifications.

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2.0 PRODUCT
2.1 Fabrication
2.1.1 Materials
All materials of the Vertiv™ Liebert® STS2 shall be new, of current manufacture, high grade and free from
all defects and shall not have been in prior service except as required during factory testing.
The maximum working voltage, current and di/dt of all solid-state power components and electronic
devices shall not exceed 75% of the ratings established by their manufacturer. The operating
temperature of solid-state component subassembly shall not be greater than 75% of their ratings.
2.1.2 Wiring
Wiring practices, materials and coding shall be in accordance with the requirements of the National
Electrical Code (NFPA 70). All bolted connections of busbars, lugs and cables shall be in accordance with
requirements of the National Electrical Code and other applicable standards. All electrical power
connections are to be torqued to the required value and marked with a visual indicator.
Provision shall be made for power and control cables to enter or leave from the top or bottom of the
Liebert® STS2 cabinet.
2.1.3 Frame and Enclosure
The Liebert® STS2 unit, comprised of solid-state, three-pole, dual-position transfer switch, key-
interlocked static switch isolation and bypass MCSs, shall be housed in a single free-standing NEMA type
1 enclosure and meet IP20 requirements. The frame shall be constructed of galvanized steel and pop
riveted to provide a strong substructure. The frame shall include four heavy-duty swivel castors for ease
of installation and four permanent leveling feet for final installation. Doors and removable exterior panels
shall be a minimum of 16GA steel and be powder-painted the manufacturer’s standard color textured
enamel finish paint. A key-lock, hinged front door shall provide access to the MCSs. A tool shall be
required to remove exterior panels that expose hazardous voltages. All removable panels shall be
grounded to the frame for safety and EMI/RFI protection. The cabinet shall be structurally designed to
handle forklifting from the base.
Removable conduit/cable termination plates shall be provided in the top and bottom of the unit for
termination of the two source input and/or output conduits, raceways or cables.
The complete STS shall have maximum dimensions of [30 in./762 mm (up to 250 amps), 38.1 in./965 mm
(400A-600A,), 84 in./2134 mm (800A-100A)] wide by 32.2 in./818 mm deep by 77 in./1956 mm high.
The Liebert® STS2 can be tipped 15 degrees in any direction without falling over.
2.1.4 Cooling (100-600A)
The Liebert® STS2 shall utilize convection air cooling for the enclosure with forced air cooling of the heat
sinks. All fans shall be redundant so that a single fan failure will not cause temperature to increase beyond
acceptable limits. Individual sensor(s) are located on heat sinks for alarm and shutdown. Heat rejection
shall be through screened protective openings in the top of the unit. Air filters shall be located in the
front door at the point of air inlet.
2.1.5 Cooling (800-1000A)
Cooling of the Liebert® STS2 shall be by forced air. Low-velocity fans shall be used to minimize audible
noise output. All fans shall be redundant so that a single fan failure will not cause temperature to increase
beyond acceptable limits. Individual sensor(s) are located on heat sinks for alarm and shutdown. Heat
rejection shall be through screened protective openings in the top of the unit. Air filters shall be located
in the front door at the point of air inlet.

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2.1.6 Grounding
The Vertiv™ Liebert® STS2 shall operate from sources that are solidly grounded or impedance-grounded
(for 480V and below). The unit shall not be used on corner-grounded delta systems.
The AC output neutral shall be electrically isolated from the Liebert® STS2 chassis. The Liebert® STS2
chassis shall have an equipment ground terminal.
2.2 Components
2.2.1 Molded-Case Switches (MCS)
The Liebert® STS2 shall be equipped with five MCSs. The MCSs shall be UL listed and IEC rated for use
at the system voltage. The plug-in feature of the breaker shall include interlock, which prevents the
breaker from being unplugged without being in the Off (open) position. Three of the MCSs shall provide
for total isolation of the solid-state switching devices with an input MCS for each source and a load
isolation MCS. Two of the MCSs shall provide for maintenance bypassing of the solid-state switching
devices to either input source. Key interlocks shall be provided on the MCSs to prevent improper
maintenance bypassing of the solid-state switch. A bypass MCS cannot be closed unless the solid-state
switch is connected to the same input source, and only one bypass MCS can be closed at a time. All MCSs
shall be equipped with N.O. and N.C. auxiliary switches for monitoring of the breaker positions. The two
input MCSs for the solid-state switching devices also shall be equipped with 48 VDC shunt trips to allow
for control by the Liebert® STS2 logic.
2.2.2 Silicon Controlled Rectifiers (SCRs)
The Liebert® STS2 consist of six pairs of SCRs connected in an AC switch configuration. The SCRs shall
be brick-type and rated to carry the full 100% rated load. The SCRs shall be rated to prevent hazardous
device failure in power systems with available fault currents listed under Section 1.4.3, Item I.
2.2.3 Control Panel
The Liebert® STS2 shall be provided with a microprocessor-based Human-Machine Interface (HMI) to
configure and monitor the Liebert® STS2. The HMI shall be located on the front of the unit and can be
operated without opening the hinged front door. The HMI shall not be mounted to the front door so the
door can be easily removed for maintenance. A backlit, menu-driven, full graphics, color touch-screen
Liquid Crystal Display (LCD) shall be used to display system information, status information, a one-line
diagram of the Liebert® STS2, active alarms, alarm history information, startup and bypass instructions.
No mechanical pushbuttons shall be used.
The mimic screen shall indicate the power flow, the status of all MCSs, the preferred source and the
Liebert® STS2 position (connected to source 1 or 2) as well as active alarms.
Pop-up boxes selected from the menu bar shall be provided for operator interface to the HMI for menu
selection, control of the preferred source, manual transfer initiation, auto/manual retransfer selection and
other system setpoints. In addition, an operator can silence and reset the audible alarm by touching the
screen. To facilitate STS operation, help text, step-by-step startup, transfer and maintenance bypass
procedures shall be displayed on the LCD screen. For manual transfers, a syncscope shall display the
leading or lagging real-time phase difference between the two input sources.
The HMI shall be equipped with an internal RS232 port and Flash memory to allow the Liebert® STS2
software to be upgraded by a factory-trained customer engineer without shutting down the load.
To facilitate diagnostics, an event log of the last 512 alarm events shall be stored in non-volatile memory
and displayed on the LCD. Two history logs, each having 64 frames of unit status frozen upon an alarm
condition designated as a freeze fault, will be stored in non-volatile memory and displayable on the LCD.
A frame shall be acquired every 4 milliseconds, with 40 frames before the fault and 23 frames after the
fault. Each frame contains metering data, active alarms/faults and unit status. A system calendar and
real-time clock shall be included to time-stamp all stored events.

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CAN bus shall be used to communicate between the logic and the HMI as well as the options.
For remote monitoring, a serial RS-232 port shall provide present switch status information, alarm history
information and the history of status screens that are triggered upon a major alarm event.
Metering
The following metering parameters shall be displayed:
•Input AC voltage for both sources, line-to-line for each phase
•Input AC current for both sources for each phase
•Input frequency for both sources
•Output kVA
•Output kW
•Percent load
•Number of switch transfers
•Synchronization phase angle
All voltages and currents shall be measured using true-RMS techniques for accurate representation of
non-sinusoidal waveforms associated with computers and other electronic loads. The metering
parameters shall have a full-scale accuracy of ±2%.
Alarm Messages
Active alarms shall be monitored and displayed simultaneously as part of the LCD event panel. The
following alarm messages shall be displayed:
Source 1 Failure
CB1 (Source 1) Open
Power Supply S1 AC Failed
Source 2 Failure
CB2 (Source 2) Open
Power Supply S2 AC Failed
Sources Out of Sync
CB3 (Output) Open
Power Supply DC A Failed
Source 1 Overvoltage
CB3A Open (If used)
Power Supply DC B Failed
S1 Undervoltage (fast)
CB4 (S1 Bypass) Closed
Power Supply Logic Failed
S1 Undervoltage RMS (slow)
CB5 (S2 Bypass) Closed
S1 Voltage sense module failed
Source 2 Overvoltage
CB1 Shunt trip fail
S2 Voltage sense module failed
S2 Undervoltage (fast)
CB2 Shunt trip fail
S1 SCR sense module failed
S2 Undervoltage RMS (slow)
S1 SCR Open
S2 SCR sense module failed
Source 1 Overcurrent
S2 SCR Open
S1 Current sense module failed
Source 2 Overcurrent
S1 SCR Shorted
S2 Current sense module failed
Source 1 Over/Under
Frequency
S2 SCR Shorted
S1 Gate drive module failed
Source 2 Over/Under
Frequency
Primary fan failure
S2 Gate drive module failed
Source 1 Phase Rotation Error
Control Module Fail
Internal comm failed
Source 2 Phase Rotation Error
S1 I-peak
Option comm failed
Output undervoltage
S2 I-peak
Output voltage sense module
failed
STS on alternate source
Auto Retransfer Inhibit
Heatsink Overtemp
Transfer Inhibit
An audible alarm shall be activated when any of the alarms occurs. All alarms shall be displayed in text
form.

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2.3 Accessories (Optional Components and Services)
2.3.1 Optimized Transfer
The Vertiv™ Liebert® STS2 shall be furnished with an optimized transfer control algorithm. This algorithm
shall optimize the Liebert® STS2 transfer timing such that the volt-seconds applied to a downstream
transformer(s) primary is balanced, thus sufficiently minimizing peak saturation current drawn by the
downstream transformer(s).
In addition to controlling the transformer primary current and flux, the optimized transfer control
algorithm must maintain the load voltage within the CBME/ITIC Standards during the transfer. To
maintain load voltage after the preferred source is turned off, the control algorithm must be able to pulse-
fire the alternate source SCRs to minimize load discontinuity and voltage disruption.
The Liebert® STS2 must maintain the above specification under the following conditions:
1. Loss of source
2. Loss of a single phase
3. Voltage droop
4. Phase-to-neutral short
5. Phase-to-phase short
6. Power factor load range of 0.75 to 1.0 leading or lagging
7. Out-of-phase conditions from +180 to -180
2.3.2 Programmable Relay Board
A Programmable Relay Board with eight sets of isolated Form C contacts shall be provided to indicate a
change of status of any alarm condition. Any alarm can be programmed onto any channel or channels.
Up to two programmable relay boards can be installed in the Liebert® STS2. Programming is performed
through the touch screen display. Each contact shall be rated 1A @ 30 VDC or 250mA @ 125 VAC.
2.3.3 Input Contact Isolator Board
An Input Contact Isolator Board with eight relay inputs (normally open dry contacts) shall be provided
for owner alarm messages. The owner, through the touch screen display, can program the alarm
messages.
2.3.4 Communications Board
The Liebert® STS2 shall be provided with a Communications Board that can communicate with a Vertiv™
Liebert® SiteScan™ monitoring system.
The Liebert® STS2 shall be equipped with an RS-422 communication port for communication to a Liebert®
SiteScan™ monitoring system using a 2-wire twisted pair for reliable communication up to 3281 ft.
(1000m). Information available from the RS-422 port shall include the present switch status information,
all monitoring parameters and all active alarms.
2.3.5 Vertiv™ Liebert® IntelliSlot IS-UNITY-DP Card
The Vertiv Liebert® PPC shall be supplied with an IS-UNITY-DP Card for remote communication using
two of the following protocols: HTTP/HTTPS, Emerson Protocol, Email, SMS, SNMP v1/v2c/v3, BACnet
IP/MSTP and Vertiv™ Liebert® Modbus TCP/RTU output. A serial RS-485 two wire connector shall be
supplied.
NOTE: Two of the 3rd party protocols (SNMP, Modbus or BACnet) may be configured and used
simultaneously. Liebert® Modbus RTU and BACnet MSTP cannot both be enabled simultaneously.

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2.3.6 Remote Source Selection
The Vertiv™ Liebert® STS2 shall be furnished with Remote Source Selection board to remotely select the
preferred source. Closure of one of the two N.O. dry contacts (by others) shall cause the selected source
to be the preferred source to which the Liebert® STS2 will connect the load as long as the source is
available in the same manner as the local source transfer selection. If both input contacts are closed, the
current selected preferred source shall be retained. If the unit preferred source selection and remote
source selection shall be active at the same time, the Liebert® STS2 follows the last request for a
preferred source change, regardless of whether it was from the local or remote source select controls.
2.3.7 Key Lockout Switch
A key lockout switch shall be provided which activates a software lockout of the touch-screen display to
prevent manual transfers and configuration changes. When locked out, the touch screen becomes a read-
only display and a key is required to do manual transfers or change settings. The alarm silence button
shall not be disabled when in the lockout position. The switch shall be located behind the front door but
can be operated without opening the front door.
2.3.8 Redundant Output MCS
A redundant output plug-in, MCS shall be provided and connected in parallel with the output plug-in,
MCS to provide redundancy in the output power path. The redundant MCS shall be of the same rating
and type as the output MCS.
2.3.9 Input Junction Boxes and Cables
Two input power junction boxes and interconnecting cables shall be furnished for the input power
connections. Power terminal blocks shall be provided in each input junction box for the connection of the
input power conductors and a parity-sized ground conductor. The junction boxes shall be NEMA type 1
enclosure with maximum dimensions of 16 in. (406 mm) width, 30 in. (762 mm) length, and 6 in. (153 mm)
height. An input cable assembly shall be provided for connection between the Liebert® STS2 unit and the
junction box. The cable length between the unit and junction box shall be 10 ft. (3m) long and consist of
the appropriate number and size of conductors inside UL/CSA listed liquid-tight, flexible metal conduit.
The conductors shall be UL/CSA listed 90C minimum insulation, copper conductors, sized in
accordance with the NEC, based on the Liebert® STS2 input MCS ampacity.
2.3.10 Seismic Floor Anchors
The Liebert® STS2 shall be provided with seismic floor anchors to fasten the unit to a concrete floor to
meet seismic IBC 2018 requirements.
2.3.11 Floor Stand
A Floor Stand shall be furnished to level the unit and to provide bottom cabling access without relying
on a raised floor for support. The nominal height of the floor stand shall be [18 in. (457mm), 24 in. (610mm),
30 in. (762mm), 36 in. 914mm)].
2.3.12 Output Distribution Cabinet (100-600A units only)
An output distribution cabinet shall be furnished that may be mounted on the side of the Liebert® STS2.
It shall be a full-height section with hinged doors to allow for easy access.
The output distribution cabinet shall contain one vertically mounted I-line panelboard for distribution to
the intended loads. The panelboard shall be totally enclosed with an accent cover that provides access
to the panelboard without exposing other portions of the unit. The panelboard shall provide space for
100A through 250A three-pole branch MCSs. The panelboard shall include separate isolated neutral
busbar and safety-ground busbar for the neutral and safety-ground connections.
2.3.13 Certified Test Report
A certified copy of the factory test report shall be provided for each unit.

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2.3.14 Factory Witness Test
The owner and/or the owner’s representative shall attend a factory test of each unit. The factory will
perform its standard witness test to demonstrate that the unit meets the Vertiv™ Liebert® STS2
specification.
2.3.15 Export Crating
Heavy-duty solid wood crating with vapor barriers and desiccant shall be provided to meet international
requirements regarding package strength and markings for overseas shipments.

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3.0 EXECUTION
3.1 Field Quality Control
The following inspections and test procedures shall be performed by factory-trained field service
personnel during the Vertiv™Liebert® STS2 startup.
3.1.1 Visual Inspection
•Inspect equipment for signs of damage.
•Verify installation per drawings.
•Inspect cabinets for foreign objects.
•Verify neutral (if used) and ground conductors are properly sized and configured.
•Verify all printed circuit boards are configured properly.
3.1.2 Mechanical Inspection
•Check all control wiring connections for tightness.
•Check all power wiring connections for tightness.
•Check all terminal screws, nuts and spade lugs for tightness.
3.1.3 Electrical Inspection
•Check all fuses for continuity.
•Confirm input voltage and phase rotation is correct.
•Verify control transformer connections are correct for voltages being used.
3.2 Manufacturer’s Field Service
3.2.1 Service Personnel
The Liebert® STS2 manufacturer shall directly employ a nationwide service organization, consisting of
factory-trained field service personnel dedicated to the startup, maintenance and repair of UPS and
power equipment. The organization shall consist of regional and local offices.
The manufacturer shall provide a fully automated national dispatch center to coordinate field service
personnel schedules. One toll-free number shall reach a qualified support person 24 hours/day, 7
days/week, 365 days/year. If emergency service is required, response time shall be 20 minutes or less.
An automated procedure shall be in place to ensure that the manufacturer is dedicating the appropriate
technical support resources to match escalating customer needs.
3.2.2 Replacement Parts Stocking
Parts shall be available through an extensive network to ensure round-the-clock parts availability
throughout the country.
Recommended spare parts shall be fully stocked by local field service personnel with backup available
from the national parts center and the manufacturing location. The national parts center Customer
Support Parts Coordinators shall be on call 24 hours/day, 7 days/week, 365 days/year for immediate
parts availability. Parts from the national parts center shall be shipped within 4 hours on the next
available flight out and delivered to the customer’s site within 24 hours.

Vertiv™ Liebert® STS2
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Proprietary and Confidential © 2021 Vertiv Group Corp.
3.2.3 STS Maintenance Training
Maintenance training courses for customer employees shall be made available by the Vertiv™ Liebert®
STS2 manufacturer. This training is in addition to the basic operator training conducted as a part of the
system startup.
The training course shall cover STS theory, location of subassemblies, safety and STS operational
procedures. The course shall include control, metering and feedback circuits to the Printed Circuit Board
(PCB) level. Troubleshooting and fault isolation using alarm information and internal self-diagnostics
should be stressed.
3.2.4 Maintenance Contracts
A complete offering of preventive and full-service maintenance contracts for the Liebert® STS2 shall be
available. An extended warranty and preventive maintenance package shall be available. Factory-trained
service personnel shall perform warranty and preventive maintenance service.
NOTE: These Guide Specifications comply with the format outlined by the Construction Specifications
Institute per CSI MP-2-1 and CSI MP-2-2. In correspondence, reference Liebert® document SL-
20610_REV07_05-16.