Vertiv (Liebert) Liebert STS2, ST/SR/SX series, 100-1850 A
Vertiv's Liebert STS2 static transfer switch across three chassis series, 100 to 1850 amps
Vertiv (Liebert) Liebert STS2, ST/SR/SX series, 100-1850 A is one of 4 static transfer switches tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.
Vertiv Liebert STS2 static transfer switch dossier: ST/SR/SX chassis specs, UL 1008S certification detail, transfer times, and used-market pricing analysis.
Why it matters
STS2-PDU's discontinued status and its fixed 208 V output, panelboard, and breaker build narrow its resale pool sharply against the still-active, distribution-agnostic standalone STS2, which can feed any downstream PDU a buyer already owns. Certification and warranty claims should be weighed against the specific chassis document and Vertiv's boilerplate warranty structure, not assumed from brand reputation alone.
Who buys it
Data center and colocation operators running dual-bus A/B UPS output arbitration are the core buyer, per Vertiv's own stated STS2 positioning. A second buyer type holds a first-generation Liebert STS1 installation and is sourcing the SR series specifically as Vertiv's documented replacement path, reusing existing STS1 ancillary accessories rather than re-engineering the site.
Role in the data center
Upstream of single-corded IT loads at the PDU or rack-row level, arbitrating automatically between two live A/B UPS output sources within a quarter cycle so a single-power-supply server does not see either source's loss.
Key specifications
| Current rating, ST series | 100, 250, 400, 600, 800, 1000 A |
|---|---|
| Current rating, SX series | 1200, 1250, 1400, 1600, 1800, 1850 A |
| Current rating, SR series | 400, 600 A |
| Voltage, ST/SX (NA-inclusive chassis) | 200/208/220/240/380/400/415/480/575/600, 3-phase VAC |
| Voltage, SR series | 208 or 480 VAC |
| Pole configuration | 4-pole double-throw (1250-1800A chassis) or 3-pole (1200-1850A chassis) poles |
| Short-circuit current rating, 800-1000A frame at 380-480V | 65 kA symmetrical |
| Short-circuit current rating, SX chassis at 380-480V | 100 kA symmetrical |
| Automatic (emergency) transfer time | less than 1/4 cycle |
| Manual (synchronized) transfer time | less than 1/8 cycle |
| Manual (optimized) transfer time, SX chassis | less than 1 line cycle |
| Warranty | 12 months from startup or 18 months from ship date, whichever occurs first |
| Cabinet dimensions, 1250-1800A 4P chassis | 26 W x 36 D x 81.6 H (88.0 H with top hat) in |
| Cabinet weight, SR series (unpacked) | 1200 lb |
| Standards listing, ST series | UL 1008, UL 1008S, CSA, ANSI, IEEE, ISO 9001, NEC, NEMA, NFPA 70 |
| Optional seismic compliance | IBC 2018 seismic floor anchor kit, optional accessory |
Technical summary
Amperage, ST series: 100/250/400/600/800/1000 A Amperage, SR series: 400/600 A Amperage, SX series: 1200/1250/1400/1600/1800/1850 A Voltage, ST/SX (NA-inclusive chassis): 200-600 V, 3-phase, 50/60 Hz Transfer time: under 1/4 cycle automatic, under 1/8 cycle manual synchronized, under 1 line cycle SX optimized Short-circuit current rating: 25-125 kA symmetrical, varies by voltage/amperage class Standards, ST/SX/SR: UL 1008S, UL 891, CSA C22.2 No. 178.1 Seismic: optional IBC 2018 floor anchor kit, ST series Warranty: 12 months from startup or 18 months from ship, whichever occurs first STS2-PDU: discontinued, fixed 208V output, integrated panelboard/breaker/transformer Controls: microprocessor HMI, color touchscreen LCD, CANbus, RS-232 firmware upgrade port
Configurations and options
3-pole or 4-pole double-throw configurations are both offered depending on chassis (SX series). An optional IBC 2018 seismic floor-anchor kit is available on the ST series as a separately ordered accessory, not a standard inclusion. Remote monitoring is available via either the IntelliSlot 485 Web Card ADPT (documented for ST/SX) or the newer Unity communications card (documented for SR), and firmware is field-upgradable via an internal RS-232 port without deenergizing the load.
Compatibility and dependencies
The SR series (400A/600A) is compatible with existing Liebert STS1 ancillary accessories per an independent reseller page, supporting its position as a direct STS1 replacement. Vertiv's own documents do not confirm whether the newer Unity communications card can be retrofitted into an older ST/SX chassis card slot originally documented with the IntelliSlot 485 Web Card ADPT; this should be confirmed directly with Vertiv rather than assumed.
Pricing and availability
Comparable secondary-market band: 4.16–14.75 $ per ampere. Trend: flat Warranty, new: 12 months from startup or 18 months from ship date, whichever occurs first — Vertiv-wide boilerplate warranty structure, not an STS2-specific commitment (see notes).
Common failure points
- SCR/thyristor pairs — Failure to open cleanly, creating risk of momentary cross-connection between the two live sources
- Gate driver boards — SCR misfire, erratic or failed transfer under load
- Cooling fans — Elevated cabinet temperature, nuisance thermal alarms
- Control power transformers/capacitors — Erratic HMI behavior, false alarms, intermittent logic-power dropout
- HMI touchscreen/color LCD — Unresponsive touch input, blank or frozen display
- Seismic floor anchor kit (where ordered) — Missing or improperly torqued anchors relative to the IBC 2018 specification
- Communications/network card — Loss of remote SNMP/web monitoring while the switch itself continues operating normally
Inspection checklist
HMI firmware/software revision — confirm the current release level via the RS-232 diagnostic port before energizing, and get the field-upgrade history from the seller Event log — pull the full 512-alarm event log and both 2x64-frame history logs via the HMI before purchase, and cross-check against the seller's stated service history SCR gate driver boards — inspect every gate driver board for discoloration or capacitor bulging, since thermal cycling is the documented root cause on a platform marketed for 20+ year solid-state design life Cooling fans — verify all cabinet cooling fans spin freely and are free of debris, since clogging is a named STS failure mode across the category Short-circuit current rating nameplate — confirm the SCCR nameplate matches the voltage class in service, up to 125 kA at 208-240V and as low as 25 kA at 600V per Vertiv's own rating table Seismic floor anchor kit — confirm whether the optional IBC 2018 seismic anchor kit is physically present, undamaged, and unused, since it ships as a separately ordered accessory Synchroscope/sync-window calibration — request a live demonstration of a synchronized manual transfer at the commissioned phase-window setting and confirm the actual measured transfer time rather than the nameplate 1/8-cycle figure Control power transformers and capacitors — megger-test insulation resistance, especially on units older than 15 years from their startup date Current transformer ratio — verify the installed CT ratio, commonly 1000:1 on 480V frames, matches both the nameplate and the downstream metering Startup/commissioning certificate — obtain the OEM startup date, not just the ship date, since warranty runs 12 months from startup or 18 months from ship, whichever is first Breaker cycling — manually cycle every output and bypass breaker and record trip-curve data on the 100% rated, fuseless design Bus bar and lug torque — verify every bus bar and lug connection is torqued to the OEM placard value and shows no discoloration from prior overheating Thermal imaging scan — request a thermal-imaging scan of the energized cabinet before rigging, since hotspots at SCR pairs or bus joints indicate imminent failure not visible cold Communications/network card — identify whether the installed card is the IntelliSlot 485 Web Card ADPT or the Unity communications card and confirm firmware compatibility with the buyer's monitoring platform Serial number and parts-support chain — record the full nameplate serial number and confirm current parts and service availability directly with Vertiv, since STS2-PDU is now discontinued
Regional notes
ST and SX guide specifications cover North American voltage taps (480V, 600V) alongside international taps (380/400/415V); the SL-20604 four-pole SX variant offers international voltage only, with no 480V or 600V option, which correlates with, but is not explained by Vertiv as the cause of, that document's omission of UL and seismic language.