Resource
The UPS buying guide.
Six decisions determine the right uninterruptible power supply. Here's how to make each one — in plain terms, for Indian sites.
Resource
Six decisions determine the right uninterruptible power supply. Here's how to make each one — in plain terms, for Indian sites.
Choosing an uninterruptible power supply comes down to six decisions. Get these right and the rest — brand model, battery cabinet, monitoring — follows naturally. Our engineers will walk you through all six free of charge, but here's the framework.
Add the wattage of every protected device and add 20–25% headroom. Remember kVA vs kW: with a unity (1.0) power factor, kVA equals usable watts.
Graceful shutdown (5–10 min) or ride-through to a generator? Runtime sets battery quantity and whether you need external or lithium-ion cabinets.
For servers, medical and industrial loads, online double conversion (true online) is the standard — full isolation, zero transfer time.
Edge and small IT use single-phase 1–20 kVA; rooms and data centres use three-phase scaling into the megawatt range.
Modular, pay-as-you-grow designs (APM2, EXL S1, Trinergy Cube) add power or redundancy without replacing the frame.
Higher double-conversion and ECO efficiency lowers running cost; strong AMC and local spares protect uptime for years.
Online (double conversion). The gold standard for critical loads. Power is continuously converted AC→DC→AC, so the output is a clean, regenerated sine wave and the transfer to battery is instantaneous. This is what every Vertiv Liebert online UPS on this site uses.
Line-interactive. Regulates voltage with an autotransformer and switches to battery on failure. Good for small office and home loads, but there is a brief transfer time and less isolation from mains noise.
Offline / standby. The simplest and cheapest; the load runs on raw mains until power fails, then switches to battery. Suitable only for non-critical desktop equipment.
For servers, healthcare, industrial control and finance, online double conversion is the right — and usually the only appropriate — choice.
kVA is apparent power (what the UPS is rated for); kW is real power (what your equipment actually consumes). The ratio between them is the power factor. Modern Liebert units deliver a unity (1.0) output power factor, so kVA equals kW — a 100 kVA unit supplies 100 kW.
Double-conversion efficiency (up to ~97.5% on modern units) is how much input power reaches the load in full online mode. ECO mode lifts efficiency toward ~99% when the mains is clean, then reverts to full protection the instant a disturbance appears.
N is exactly enough capacity for the load. N+1 adds one spare module or unit so the system survives a single failure. 2N fully duplicates the system for the highest uptime tiers. Modular UPS such as Liebert APM2 make N+1 straightforward.
FAQ
An online UPS uses double-conversion topology — incoming AC is continuously converted to DC and back to clean AC, so the load is fully isolated from mains disturbances with zero transfer time to battery. Line-interactive and offline UPS switch to battery only when they detect a problem, which introduces a brief break and passes through more mains noise.
Add the wattage of every device the UPS must protect, then add 20–25% headroom for growth. UPS capacity is rated in kVA while real power draw is in kW; modern Liebert units with a unity (1.0) power factor deliver kVA equal to kW, so a 20 kVA unit supplies 20 kW.
Decide whether you need a graceful shutdown (typically 5–10 minutes) or ride-through until a generator starts. Runtime drives battery quantity and whether you need external or lithium-ion battery cabinets.
Small IT and edge sites usually use single-phase 1–20 kVA units. Larger rooms and data centres move to three-phase systems that scale from tens of kVA into the megawatt range.
Lithium-ion offers a longer lifecycle, faster recharge, a smaller footprint and lower total cost of ownership; VRLA has a lower upfront cost. Many current Liebert models are lithium-ready, and Vertiv HPL cabinets provide scalable lithium energy storage.
Double-conversion efficiency is how much input power reaches the load in full online mode — modern Liebert units reach up to 96–97.5%. ECO mode raises efficiency to around 99% when the mains is clean, reverting to full protection instantly on any disturbance.
Talk to an engineer
Skip the guesswork — share your load and site details and we'll recommend the exact Vertiv Liebert model, runtime and options.