Vertiv UPS Buying Guide: Double-Conversion Systems up to 40kVA
Scope note: This guide covers double-conversion (online) UPS systems up to 40kVA only. Line-interactive and standby topologies are excluded because they are unsuitable for the critical loads and runtime requirements discussed here. Larger three-phase data centre UPS platforms - such as the Liebert APM/APM2, EXL S1, PowerUPS 9000, and Trinergy Cube - will be covered in a separately.
Choosing a UPS in this range is not simply a matter of matching a kVA number to a load. It requires understanding battery autonomy at Start of Life (SOL) and End of Life (EOL), how runtime changes with connected load, where the UPS will live, how it will be monitored, how it will be serviced without downtime, and what maintenance regime will keep it reliable.
Part 1: Battery Autonomy — SOL, EOL, and Load Dependence
SOL vs. EOL Runtime
SOL Runtime is the backup duration delivered by new batteries at a specified load and temperature. This is the figure usually quoted in brochures.
EOL Runtime is the backup duration when the battery has reached the end of its useful life. For VRLA batteries, end of life is generally defined as the point where the battery can no longer supply 80% of its rated capacity. For lithium-ion, EOL is typically defined by capacity falling to a specified percentage of the original rating, often 80% or lower depending on the manufacturer.
A UPS specified for 90 minutes SOL may deliver only 60–70 minutes at EOL if the battery degrades by 20–30%. This gap must be designed for.
Runtime Depends on Connected Load
Battery runtime is not a fixed number. It depends on the actual load connected to the UPS. The same battery bank will deliver longer runtime at a lighter load and shorter runtime at a heavier load.
For example, a 10kVA UPS with a given internal battery configuration might deliver:
100% load at 10kVA, 10 minutes
70% load at 7kVA, ~14–15 minutes
Exact figures depend on battery model, age, and temperature, but the principle is universal: specify runtime at your actual load, not at full rated capacity.
Designing for EOL, Not SOL
Define required runtime at EOL, not SOL.
If 90 minutes is required throughout battery life, size SOL runtime at 110–120% of that figure.
Prefer battery technologies with flatter degradation curves and State of Health (SoH) monitoring, such as lithium-ion.
Use the UPS’s battery management features to track State of Charge (SoC) and SoH.
Part 2: Deployment Environment
The physical environment dictates the required protection rating, thermal tolerance, and form factor of the UPS.
Office / Commercial Spaces
Recommended series: Liebert GXT5 (750VA–10kVA, single-phase)
Typical loads: Workstations, network closets, point-of-sale systems, small servers, security systems
Key considerations:
Temperature-controlled, clean environment
Standard IT-grade enclosure is sufficient
Quiet operation - under 46 dB, suitable for occupied office spaces
Rack/tower convertible design for flexible deployment
Lithium-ion option reduces footprint and maintenance visits
Internal maintenance bypass may be optional - specify it if service without load downtime is required
IT Cabinet / Edge (Three-Phase)
Recommended series: Liebert ITA2 (5–40kVA, three-phase)
Typical loads: Edge IT, small server rooms, networking equipment
Key considerations:
Compact three-phase power in a rack/tower form factor
Supports VRLA or lithium-ion external batteries for scalable runtime
Parallelable up to 80kVA load capacity in 400V configurations
Internal maintenance bypass is typically optional
External maintenance bypass cabinet required for parallel systems
Ideal where true three-phase power is needed in limited space
Industrial Environments
Recommended series: PowerUPS 6000 Industrial (6–40kVA models)
Typical loads: PLCs, SCADA systems, motor controls, process instrumentation, railway signalling
Key considerations:
IP42 rating - protects against solid objects ≥1mm and water spray at a 15° tilt
Operates reliably up to 50°C, with derating above 30°C
Conformal-coated PCBs (Triple Proof Impregnation Process) protect against dust, moisture, and corrosion
Built-in output isolation transformer on 6–40kVA models provides galvanic isolation
Dust-resistant - can be installed directly in industrial cabinet rooms without special dustproofing
LSOH (Low Smoke Zero Halogen) internal cabling for enhanced fire safety
Internal maintenance bypass is standard
Small Data Centre Room
Recommended series: Liebert EXS (10–40kVA models)
Typical loads: Small server rooms, healthcare, transportation
Key considerations:
High efficiency - up to 96.2% in double-conversion, 99% in ECO mode
Integrated autonomy - up to four internal battery strings
CPSS (EN 50171) and railway (EN 50121) certified
Integrated maintenance bypass
Parallelable up to four units for capacity or redundancy
Suitable where efficiency, space, and flexibility are priorities
Part 3: Monitoring and Software
Monitoring is an architecture that spans from the UPS to the software that aggregates and acts on data. It includes both hardware cards and software platforms.
Monitoring Hardware
| Feature | Liebert IntelliSlot Unity Card | Liebert RDU120 | Liebert RDU501 |
|---|---|---|---|
| Type | Network communication card | Network communication card | Infrastructure management appliance |
| Installation | IntelliSlot port in UPS | IntelliSlot port in UPS | Rack-mounted or standalone gateway |
| Protocols | SNMP v1/v2c/v3, Modbus TCP, BACnet/IP, Web, Telnet, SSH, RESTful API | SNMP, Modbus, BACnet, web interface | SNMP, Modbus 485, dry contacts, analog signals |
| Environmental Sensors | Temperature, humidity, leak, door contact via external sensors | Temperature, humidity, dew point, door contact, leak sensors | Up to 32 sensors (80 with THUB) |
| Device Capacity | Single UPS plus sensors | Single UPS plus sensors | Up to 64 devices (Modbus/SNMP mixed) |
| Out-of-Band Management | No | No | Yes - server service processor access |
| Best For | New deployments needing modern security, API integration, BMS/DCIM connectivity | Basic single-UPS network monitoring | Multi-device infrastructure monitoring |
Unity Card is the current-generation communication card. It provides secure, API-driven connectivity to BMS, DCIM, and NMS platforms, and supports SNMPv3, SSH, and TLS. For new deployments, it is preferred over the older RDU120.
RDU501 is a comprehensive gateway for multi-device environments, aggregating data from multiple UPSs, cooling units, and generators.
Monitoring Software
| Software | Vertiv Power Assist | Vertiv Power Insight | Vertiv Environet |
|---|---|---|---|
| Cost | Free | Free | Licensed |
| Type | Monitoring and graceful shutdown software | Monitoring and shutdown software | Enterprise monitoring platform |
| Device Capacity | Up to 2 UPSs per computer | Up to 100 rack UPSs and rPDUs | Scalable to large facilities |
| Target User | Individual computers, small server rooms, edge IT, labs | Distributed IT, edge sites, small data centres (<25 racks) | Enterprise data centres, multi-site facilities |
| Key Features | Graceful shutdown, alerts, logging, maintenance mode, scripted shutdown, auto-discovery via USB or SNMP | Alarming, trending, automated shutdown, dashboard | Comprehensive power, cooling, and environmental monitoring; multi-vendor support |
| Supported UPS Models | Liebert PSI, PSI5, EDGE, PSA, PSA5, PST5, GXT3, GXT4, GXT5 | GXT3, GXT4, GXT5, APS, APM, eXM, ITA2, EXS (select models) | Broad Vertiv and third-party infrastructure |
| Best For | Single computers and small edge deployments | Small to medium distributed IT | Large or multi-site deployments |
Power Assist is a free monitoring and shutdown software, not a load-handling or overload-assist feature. It runs on a computer or server connected to the UPS and gracefully shuts down IT devices when the UPS battery reaches a threatening condition. It is typically used with single-phase UPS models such as the GXT5.
Power Insight is a free, web-based monitoring platform for distributed IT. It supports up to 100 devices and provides alarming, trending, and automated shutdown.
Environet is the licensed enterprise platform for comprehensive data centre monitoring.
Connectivity Chain
A Unity Card or RDU120 enables communication between the UPS and Power Assist, Power Insight, Environet, and LIFE Services for remote diagnostics. Start with the appropriate card and software for your scale, and expand as needed.
Part 4: Bypass Features - Internal and External Maintenance Bypass
A maintenance bypass allows the UPS to be taken offline for service, battery replacement, or module swaps while the load continues to receive power from the mains.
Internal Bypass
Most double-conversion UPS systems include an internal maintenance bypass as standard or optional. When closed, it routes mains power directly to the load, bypassing the rectifier, inverter, and static switch. The UPS can then be fully isolated for service while the load remains powered.
GXT5: Confirm whether internal maintenance bypass is standard or optional for the specific model.
ITA2: Internal maintenance bypass is typically optional.
PowerUPS 6000 Industrial: Standard switch includes maintenance bypass.
EXS: Integrated maintenance bypass.
External Bypass
An external maintenance bypass switch (EMBS) is used when the internal bypass is insufficient. This is required for:
Parallel UPS systems - for example, ITA2 units paralleled for capacity or redundancy up to 80kVA.
Larger ratings within the 40kVA scope where the internal bypass is not rated for full load current.
Redundant configurations where one UPS must be serviced while others continue protecting the load.
Part 5: Service and Maintenance Regime
A UPS is a long-term asset. Reliability depends on a proactive maintenance programme.
Service Programme Components
24×7 access to the Emergency Service Centre.
Guaranteed 2–4 hour on-site emergency response, 24/7, within 100 km of a Vertiv “service city.”
One annual preventive maintenance visit covering UPS and battery health (scheduling varies by programme).
Parts coverage, including internal batteries (limits may apply).
100% labour and travel coverage, 24/7.
Service by Vertiv factory-trained technicians (OEM for Liebert® products).
Preventive maintenance scope (UPS): visual inspection, temperature checks on breakers and connections, terminal tightening, cleaning, alarm circuit check, operational test (transfer and battery discharge), output voltage verification.
Preventive maintenance scope (batteries): inspect cabinet and connections, check for swelling/leaks/corrosion, clean cell tops, tighten terminals, measure DC bus ripple and float voltage, record room temperature.
Exclusions: air filters, proactive full bank capacitor replacement, fan replacement.
Battery Replacement Planning
Regular battery health checks during annual preventive maintenance.
Predictive replacement planning using SoH tracking on lithium-ion systems; VRLA typically has a 3–5 year life expectancy.
Recharge batteries every 6 months if not in use. Do not leave UPS switch ON for more than 2 days without AC power. Warranty is void if batteries are discharged below the minimum cutoff.
Lifecycle assessment at year 5–7: repeated battery replacements may approach the cost of a new, more efficient UPS.