Specifications

Liebert Static Transfer Switch
2 Guide Specification
The STS shall be UL and UL listed per UL Standard 1008 for Automatic Transfer Switches.
The STS shall comply with the latest FCC Part 15 EMI emission limits for Class A computing devices
and the emission limits of EN50091-1, 2, 3 Class A.
The STS 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)
• Electrostatic discharges (ESD) up to 10 kV at any point on the exterior of the unit
• Electromagnetic fields from portable transmitters within 3 feet (1 meter) of the unit
The STS2 shall comply with the immunity requirements of EN50082-1.
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.
Non-automatic circuit breaker – A circuit breaker which 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
A. Voltage. Input/output voltage specifications of the STS shall be [(200) (208) (220) (240) (380) (400)
(415) (480) (600) ( )]volts, three phase, (60) (50) Hz, (3) (4)-wire plus ground.
B. Output Load Capacity. Specified output load capacity of the STS shall be (100) (250) (400) (600)
(800) (1000)A. The STS 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. All transfers, including sense and transfer times, shall have less than a 1/4 cycle
interruption in power to the load.
The Static Transfer Switch is fuseless and consist of 6 pairs of Silicon Controlled Rectifiers (SCRs)
connected in an AC switch configuration. The brick type SCRs are continuous rated to carry 100% the
STS rated load while operating within the STS 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 STS is energized. The STS shall be
supplied with factory default settings; mechanical trim pots shall not be used for calibration or adjusting