Choosing a UPS is really five decisions: how big, how long, how critical, which battery, and how much redundancy. Get these right and everything else follows. Here is the vendor-neutral version.
1. Size the load (kVA and kW)
List every device the UPS must protect and add up the power draw. Nameplate ratings are usually in watts (W) or volt-amps (VA); convert using the power factor (modern IT loads are close to unity, ~0.9–1.0). Add 20–25% headroom for growth and inrush, but avoid grossly oversizing — a UPS loaded to only 10–20% runs less efficiently and wastes capital.
2. Decide the backup time (autonomy)
Runtime is set by the battery bank, not the UPS rating. Decide whether you need a few minutes to ride through brief outages and shut down gracefully, or enough time (often 5–15 minutes) for a diesel generator to start and stabilise. Longer autonomy means more batteries and space, so specify UPS and battery together.
3. Match topology to how critical the load is
- Online (double-conversion): zero transfer time, full conditioning. The default for servers, storage, medical, telecom and industrial control.
- Line-interactive: automatic voltage regulation with a few milliseconds of transfer time. Good for networks and small servers.
- Offline / standby: lowest cost, switches to battery only on failure. Fine for desktops and point-of-sale.
4. Choose the battery chemistry
- SMF / VRLA: lowest upfront cost, widely available, typically 3–5 year design life.
- Lithium-ion: 2–3× longer service life, roughly half the size and weight, faster recharge, wider temperature tolerance and a lower total cost of ownership over the system life.
5. Plan redundancy and scaling
Mission-critical sites deploy N+1 (one spare module) or fully modular UPS so a module can fail or be serviced with zero downtime, and capacity can be added as the load grows. For dual-corded IT, consider two independent UPS systems (2N).
Single-phase or three-phase?
Below ~10 kVA, single-phase is typical. Larger loads, and any site with a three-phase supply, generally use three-phase UPS for better balance and efficiency. We'll confirm the right input/output configuration during sizing.
Don't forget the surroundings
Account for ventilation and ambient temperature (battery life halves for roughly every 8–10 °C above 25 °C), floor loading, cable routing, maintenance bypass and remote monitoring (SNMP). A quick site survey saves expensive surprises later.
Let us size it for you
Share your load list, required backup time and site details and our engineers will produce a sized recommendation and quotation — free of charge, across any of the eight brands we carry.