A UPS (uninterruptible power supply) keeps your equipment running when the mains supply fails, sags or spikes, and it gives you time to shut down safely or hand over to a generator. Choosing one is easy to get wrong. Too small and it overloads, the wrong type and your equipment is exposed, and with no plan for batteries and servicing it can fail at the moment it is needed.
This guide follows the order NPS works through with customers: work out your load, choose the type, match the size, plan runtime and batteries, decide on redundancy, protect the UPS itself, and look after it once it is installed. It includes a sizing table that maps each size band to the UPS ranges NPS supplies across Australia and New Zealand.
Step 1: Work Out Your Load
List every device the UPS will carry: servers, storage, network switches, firewalls, workstations, phones and security equipment. For each one, note the power rating on the nameplate or datasheet, in watts (W) or volt-amperes (VA).
VA, Watts and Power Factor
Watts are the real power your equipment uses. VA is the apparent power. Watts equal VA multiplied by the power factor, and a UPS is rated in both, so both ratings need to cover your load. The relationship differs between models, which means two UPS units with the same VA rating can carry different loads. The NPS range shows this clearly:
- The APC Easy UPS SRV3KI is rated 3kVA/2.40kW.
- The APC Smart-UPS SRT3000XLI is rated 3kVA/2.70kW.
- The APC Smart-UPS SRT6KRMXLI is rated 6kVA/6kW.
The Smart-UPS SRT page lists a 0.9 power factor on the 2.2kVA to 5kVA models and unity on the 6kVA to 10kVA models, which is why the 6kVA unit above carries 6kW.
A Worked Sizing Example
The numbers below are an example only. Use the nameplate figures from your own equipment.
- Add up the load: two servers at 450W each, a storage array at 300W and a network switch at 100W come to 1,300W.
- Allow for growth: if you want 25% spare capacity, 1,300W multiplied by 1.25 gives 1,625W.
- Check both ratings: compare your watt figure with the UPS watt rating, and your VA figure with the VA rating. A 2kVA/1.40kW unit, such as the APC Easy UPS line-interactive 2kVA/1.40kW, has plenty of VA but only 1,400W, so it falls short. A 2.20kVA/1.98kW unit, such as the APC Smart-UPS SMT2200IC, covers it.
The right margin depends on how your site will grow, so NPS can confirm it for you as part of a sizing assessment.
Step 2: Choose the Right UPS Type
The type of UPS matters as much as the capacity. NPS supplies all the major topologies:
| Type | How it works | Best suited to | NPS examples |
|---|---|---|---|
| Standby (offline) | Stays idle until the mains fails, then switches to battery. Cost-effective and energy-efficient. | Desktops, printers and small office devices, generally under about 1,500VA | Entry-level units |
| Line-interactive | Provides battery backup plus automatic voltage regulation (AVR), so it handles sags and surges without switching to battery. | Small business servers, networking equipment and workstations | Eaton 5PX, APC Smart-UPS, Socomec Netys |
| Online double-conversion | Continuously converts incoming AC to DC and back to AC, isolating equipment from mains events with no transfer time. | Critical servers, data centres, medical equipment and industrial control systems | Eaton 9PX, APC Galaxy, Socomec Masterys, Vertiv Liebert ITA2 |
| Modular | Hot-swappable power modules in a shared cabinet, so capacity scales as needs grow and a failed module can be replaced without interrupting the load. | Data centres and large-scale critical infrastructure | Socomec Modulys GP, Eaton 93PS |
| Industrial | Online double-conversion rated for motors, variable frequency drives, non-linear loads and wide temperature ranges. | Process-critical industrial environments | Socomec Masterys IP+ |
For a deeper look at each topology, read Choosing the Right UPS Systems for Your Critical Infrastructure. You can also browse NPS’s line-interactive, online double-conversion and industrial ranges.
Step 3: Match Your Load to a Size Band
Once you know your load and the type you need, use this table as a starting point. The ranges come from the NPS product pages. They overlap, and the final choice depends on your load, runtime and environment.
| Size band | Typical use | Type to consider | NPS ranges to look at |
|---|---|---|---|
| Up to about 1.5kVA | Single PCs, point of sale, small office equipment | Standby or line-interactive | Eaton 5E (500 to 2000VA), Eaton 5S (550 to 1600VA), Eaton 5SC (500 to 1500VA), Eaton 5P (650 to 1550VA), Socomec Netys PE, APC Smart-UPS from 420VA, APC Easy UPS from 750VA |
| 1.5 to 3kVA | Small servers, storage, VoIP and network equipment | Line-interactive or online | Eaton 5PX (1500 to 3000VA), Eaton 9130 (700 to 3000VA), Socomec Netys PR (1000 to 2000VA), APC Smart-UPS up to 3kVA, Vertiv Liebert GXT5 Lithium-Ion (1000 to 3000VA) |
| 3 to 10kVA | Server rooms, edge sites and laboratories | Online double-conversion | Eaton 9PX, Eaton 9E (1 to 20kVA), Smart-UPS SRT (2.2 to 10kVA), Vertiv Liebert GXT5 (5 to 10kVA), Socomec Itys (1000 to 20000VA), Socomec Netys RT2 (1100 to 11000VA) |
| 10 to 40kVA | Larger server rooms and small data centres, usually three-phase | Online double-conversion | APC Galaxy VS (10 to 40kVA), APC Easy UPS 3S (10 to 40kVA), Vertiv Liebert EXS (10 to 40kW), Eaton 9155 (8000 to 15000VA) |
| 40kVA and above | Data centres and large critical facilities | Online or modular | APC Easy UPS 3M (60 to 200kVA), APC Easy UPS 3L (250 to 600kVA), Eaton 93PS, Eaton 93PM, Eaton 9395 Xpert, Socomec Modulys GP (25 to 600kVA) |
Three-phase UPS systems suit larger loads and three-phase supplies, and the NPS range includes 400V models. If you are not sure whether your site needs single-phase or three-phase, ask NPS to check before you buy.
Step 4: Plan Runtime and Batteries
Runtime is how long the UPS carries your load on battery. It depends on the battery capacity and on how heavily the UPS is loaded, and manufacturers publish run-time ratings in minutes for packaged UPS systems. Decide what you actually need the runtime for:
- Enough time to shut systems down cleanly.
- Enough time to ride through until a generator starts and takes over.
- A longer period of continued operation.
If the standard runtime is not enough, runtime can often be extended. The Eaton 9E accepts up to four external battery modules, and the Socomec Netys RT2 offers optional battery extension modules that can be added after installation.
VRLA or Lithium-Ion Batteries
The two common technologies are VRLA (valve-regulated lead acid) and lithium-ion. NPS guidance is that VRLA batteries typically last 3 to 5 years and lithium-ion batteries typically last 8 to 10 years, with lithium-ion costing more up front. The VRLA versus lithium-ion guide compares them in detail.
Two practical points affect any battery:
- Temperature: UPS batteries have a rated capacity at an ambient temperature of 20°C or 25°C, and operating outside that range can reduce performance and lifespan.
- Replacement: batteries are the part of a UPS most likely to fail and the part least likely to warn you before they do. Plan testing and timely replacement from day one, and know the signs your batteries need replacing.
Step 5: Decide How Much Redundancy You Need
Redundancy means adding duplicate capacity so one failure does not take your load down. The common levels are:
- N: the minimum capacity needed, typically a single UPS module with no redundancy.
- N+1: the base capacity plus one backup, so if one module goes offline the load is shared across the rest.
- 2N: two completely independent systems, so an entire UPS group can fail and the load stays supplied.
Several UPS ranges are built for this. The Socomec Netys RT2 supports a 1+1 parallel redundant configuration, the Socomec Masterys BC allows two UPS units in parallel for 1+1 redundancy, and the Modulys GP modular range lets capacity grow in steps from 25 to 600kVA. Read Navigating UPS Redundancy for the full set of configurations.
A generator is a companion to a UPS, not a replacement. The UPS carries the load instantly when the supply fails, and the generator sustains it for as long as it has fuel. Critical sites specify the two together.
Protect the UPS Itself
A UPS protects against loss of supply and poor power quality, but it is not rated to absorb the energy of a lightning-induced transient. Surge protective devices installed upstream clamp the transient before it reaches the UPS, and the UPS then carries the load if the supply fails. Read Lightning Protection Systems and Surge Protection and UPS vs Surge Protection to see how the two fit together.
Installation, Commissioning and Servicing
A well-chosen UPS still needs to be installed and looked after properly.
- Installation: the environment matters, including temperature and ventilation, and the UPS needs to be wired correctly from input power through to the load, battery and accessories. NPS handles installation and commissioning, including battery and load tests to confirm the UPS can carry its load. See also why correct installation and commissioning matter.
- Servicing: NPS recommends service frequency based on size and criticality. A small office UPS under 3kVA needs an annual inspection with a battery check every 6 months. A mid-range UPS (3kVA to 20kVA) needs a comprehensive service every 6 months. A large and critical UPS (20kVA and above) needs quarterly inspections, and mission-critical installations need a custom schedule with 24/7 monitoring options. Read more about UPS preventative maintenance and battery maintenance and replacement.
- Site checks: a power quality audit assesses your power infrastructure, including voltage, harmonics and transients, so the UPS is matched to what is actually happening on site.
Choosing a UPS Supplier in Australia
NPS is an authorised partner of Eaton, APC by Schneider Electric, Socomec and Vertiv, which gives access to the full UPS ranges of four leading manufacturers. NPS takes a vendor-agnostic approach, recommending the right UPS for your environment and load requirements, and its technicians are factory trained to service all the major brands. NPS has more than 30 years of experience supplying and servicing UPS systems across Australia and New Zealand, with offices in Sydney, Melbourne, Brisbane and Perth. For projects that span power, cooling and monitoring, NPS also delivers turnkey power solutions.
Common UPS Buying Mistakes
- Sizing on the VA rating alone and ignoring watts.
- Sizing for today’s load with no allowance for growth.
- Choosing the type on price alone, rather than on how sensitive the equipment is.
- Having no plan for batteries, including testing, temperature and replacement.
- Not checking that the runtime covers a clean shutdown or a generator start.
- Forgetting surge protection upstream of the UPS.
- Installing in a hot or poorly ventilated space.
- Skipping commissioning and regular servicing.
A UPS Buyer’s Checklist
- What equipment will the UPS carry, and what are its watt and VA ratings?
- How much growth should the UPS allow for?
- Does the equipment need standby, line-interactive or online protection?
- Is the supply single-phase or three-phase?
- Do you need a tower, a rack-mount or a floor-standing unit?
- How long must the UPS run on battery?
- Will you use VRLA or lithium-ion batteries, and who will replace them?
- Do you need redundancy, or a generator behind the UPS?
- Is surge protection installed upstream?
- Who will install, commission and service it?
Frequently Asked Questions About Buying a UPS
What size UPS do I need?
Add up the watt rating of every device the UPS will carry, allow for growth, and choose a UPS whose watt rating and VA rating both cover that total. The size band table in this guide shows which NPS ranges suit each load.
What is the difference between VA and watts?
Watts are the real power your equipment uses. VA is the apparent power. Watts equal VA multiplied by the power factor, so a UPS is rated in both and both ratings need to cover your load.
What is the difference between a line-interactive and an online UPS?
A line-interactive UPS provides battery backup with automatic voltage regulation and suits small business servers and networking equipment. An online double-conversion UPS continuously converts power and isolates equipment from all mains events with no transfer time, and suits critical servers, data centres, medical equipment and industrial control systems.
How long will a UPS run on battery?
It depends on the battery capacity and the load. Manufacturers publish run-time ratings in minutes, and runtime can often be extended with additional battery modules. Decide whether you need time for a clean shutdown, time to ride through to a generator start, or longer.
How long do UPS batteries last?
NPS guidance is that VRLA batteries typically last 3 to 5 years and lithium-ion batteries typically last 8 to 10 years. Temperature, usage and maintenance all affect this, so regular battery testing is important.
Do I need a UPS if I have a generator?
Yes, for critical equipment. A generator takes time to start, while a UPS carries the load instantly. The UPS carries the load through the switchover and the generator sustains it, so critical sites use both.
Should I choose a single-phase or a three-phase UPS?
Smaller loads generally use single-phase units, while larger loads and three-phase supplies suit three-phase UPS systems. NPS can check your supply and load to confirm which is right for your site.
Is a surge protector the same as a UPS?
No. A surge protector defends against surges but does nothing during a blackout, while a UPS keeps equipment running when the supply fails. Surge protection is also needed to protect the UPS itself, so critical sites need both.
How often should a UPS be serviced?
NPS recommends an annual inspection with a battery check every 6 months for a small office UPS under 3kVA, a comprehensive service every 6 months for 3kVA to 20kVA, and quarterly inspections for 20kVA and above. Mission-critical installations need a custom schedule.
Can NPS help me choose and size a UPS?
Yes. NPS recommends the right UPS for your environment and load requirements and supplies, installs and services UPS systems across Australia and New Zealand.
Talk to NPS About Your UPS
Whether you are protecting a single comms rack or a full data centre, NPS can size, supply, install and maintain the right UPS for your site. Explore the full UPS systems range, or contact the team to talk through your load.