Vertiv™ | Liebert
®
STS2
™
100-1000A, 50/60Hz User Manual | Rev. 12 | 11/2017 55
8.1.2 Reliability and Agency Requirements
The Liebert STS2 is designed for high reliability and high availability with a critical bus Mean Time Between
Failure (MTBF) exceeding 1,000,000 hours.
The Liebert STS2, Control/Power Module and all its options are designed, tested and certified, where applicable,
to meet agency requirements as follows:
• UL 1008: Transfer Switch Equipment, for UL and ULc listing
•NEC
• FCC Part 15 EMI emission limits for Class A computing devices.
The Liebert STS2 uses conservatively rated components, minimizing the need to go to maintenance bypass. All
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 Liebert STS2 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 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 15.1.5 - Electrical Requirements.
8.1.3 Factory Backup and Service Assistance
Because improper installation can cause a system to fail, a Vertiv Services service technician should thoroughly
inspect the unit to ensure it is properly installed and its operating parameters are properly configured.
Once the Liebert STS2 is properly installed, you, as the on-site operator, can easily monitor the unit’s operation
utilizing the touchscreen or LED’s.
If you need assistance, or have questions, contact Vertiv Services at 800-543-2378.
8.2 Modes of Operation
8.2.1 Normal (Preferred Source)
Under normal operating conditions, the Liebert STS2 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
8.2.2 Transfer
Should the preferred source fail or be outside acceptable voltage limits, the Liebert STS2 transfers the input to
the alternate source until the problem is rectified in the preferred source. The unit can be set to automatically
transfer the input back to the preferred source, or only allow the transfer to be done manually.
8.2.3 Transfer Inhibit
For a transfer to be completed between input sources, the sources must meet certain parameters, or the transfer
cannot take place. Uninterrupted transfer between sources is inhibited due to input source failure, sources out of
sync, switch failure, or the unit is in bypass mode.
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