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Introduction to STS2/PDU Operations
70
8.1.2 Reliability and Agency Requirements
The STS2/PDU is designed for high reliability and high availability with a critical bus Mean Time
Between Failure (MTBF) exceeding 1,000,000 hours.
The STS2/PDU and all its options are designed, tested and certified, where applicable, to meet agency
requirements as follows:
• UL 891: Standard for Switchboard, for UL and ULc listing
• UL 1008: Standard for Automatic Transfer Switches
• UL 67: Standard for Panelboard
• UL 1561: Standard for Dry Transformers
• UL 1459: Telephone equipment (Modem)
•NEC
• FCC Part 15 EMI emission limits for Class A computing devices.
The STS2/PDU uses conservatively rated components, minimizing the need to go to maintenance
bypass. All normal maintenance and repair work can be done through the front panel of the unit. This
access makes repairs and maintenance easier.
Gating and control logic are partitioned so that failure of one source’s gating or sensing logic does not
prevent the switch from transferring to the other source.
All control and logic components are mounted separate from the power components. The STS2/PDU is
designed to minimize the exposure of hazardous voltages to allow safe servicing of the unit while the
load is energized.
All electrical components requiring normal maintenance are replaceable without de-energizing the
load, as long as one source is available. Solid-state switching devices are packaged to allow safe repair
of those devices without having to de-energize the load. All non-automatic switches or circuit breakers
are the plug-in or draw-out type to allow replacement without de-energizing the load. All other com-
ponents, including transformers, power cables and connections, circuit breaker bases, etc., are
replaceable from the front, rear or top of the unit—however, this requires all power to be removed
from the unit for safety. All solid-state power switching devices are rated to prevent hazardous device
failure in power systems with available fault currents up to the defined limits, as listed in 14.1.6 -
Electrical Requirements.
8.1.3 Factory Backup and Service Assistance
Because improper installation can cause a system to fail, a Liebert Global Services or a factory
trained service technician should thoroughly inspect the unit to ensure it is properly installed and its
operating parameters are properly configured.
Once the STS2/PDU is properly installed, you, as the on-site operator, can easily monitor the unit’s
operation utilizing the touch screen.
In the United States, if you need assistance or have questions, call 1-800-LIEBERT (1-800-543-2378).
Outside the 48 contiguous United States, contact Liebert Global Services, if available in your area.
For international areas not covered by Liebert Global Services, the Liebert authorized distributor can
provide technical support.
8.2 Modes of Operation
8.2.1 Normal (Preferred Source)
Under normal operating conditions, the STS2/PDU routes power from the preferred input source to
the output load. The unit monitors the voltage current and phase of each source to ensure that both
are operating within set tolerances and that the alternate source is available, should a transfer be
required.