The Ultimate UPS Buying Guide

Everything You Need to Choose the Right UPS

An Uninterruptible Power Supply (UPS) is one of the most cost-effective pieces of protection you can specify for valuable electronics. Choosing the wrong one wastes money and leaves equipment exposed. This guide walks through every decision you need to make: topology, load calculation, runtime, battery technology, waveform type, Australian outlet configurations, and the right UPS for specific use cases including NBN and network equipment.

Guide Index

What a UPS Actually Does

A UPS has two jobs. First, it provides battery backup power when mains electricity fails, giving connected equipment time to shut down cleanly or continue operating through a short outage. Second, it conditions the incoming power, protecting equipment from the full range of power quality problems that occur constantly on the mains supply, most of which are invisible and cause slow cumulative damage rather than obvious failures.

A surge protector only handles one of these problems. A UPS handles all of them.

Power Problems a UPS Protects Against

Power Problem Description UPS Protection
Blackout Total loss of mains power. Switches to battery instantly. Provides runtime to save work and shut down cleanly.
Surge / Spike Brief intense voltage spike, often from lightning or large appliances switching on. Absorbs and clamps excess voltage before it reaches connected equipment.
Brownout / Sag Sustained low voltage, common during peak demand periods or on long cable runs. Line interactive and on-line UPS boost voltage without drawing on battery. Standby UPS switches to battery.
Over Voltage Sustained high voltage, damaging to sensitive electronics over time. Line interactive and on-line UPS trim voltage to safe levels without switching to battery.
Line Noise Electrical interference from motors, fluorescent lighting, and nearby equipment on the same circuit. UPS filters incoming power, delivering a clean stable signal to connected equipment.
Frequency Variation Deviation from the standard 50Hz supply frequency, more common with generator power. On-line double-conversion UPS regenerates a perfect 50Hz signal regardless of input frequency.

The 3 Main UPS Topologies

Topology is the single most important decision when specifying a UPS. It determines the level of protection, the transfer time to battery, and the cost.

Topology How It Works Transfer Time Best For Our Range
Standby (Offline) Monitors incoming power and switches to battery on detection of a major problem. Equipment runs directly from mains at all other times. 4–10ms Home offices, NBN equipment, modems, workstations where budget is a priority. Shop Standby UPS
Line Interactive Includes an Automatic Voltage Regulator (AVR) that handles brownouts and over-voltage without using the battery. Only switches to battery for complete power loss. 2–4ms Business workstations, office servers, POS systems, network closets, small IT rooms. The best all-rounder for most commercial applications. Shop Line Interactive UPS
On-Line (Double Conversion) Equipment never connects to mains directly. Power is continuously converted from AC to DC through the battery, then back to AC. Zero transfer time. Delivers perfect power 100% of the time. 0ms Mission-critical servers, medical equipment, sensitive IT infrastructure, any equipment that cannot tolerate any power interruption or variation. Shop On-Line UPS

How to Choose the Right UPS: Step by Step

Step 1: List Everything You Are Protecting

Write down every device that will connect to the UPS: computers, monitors, servers, switches, routers, modems, storage, displays. Do not include devices like printers or desk lamps that do not need battery backup. Only include equipment that must keep running or shut down cleanly during an outage.

Step 2: Calculate Your Total Load in Watts

Find the watt rating for each device on the nameplate or in the specifications. Add them together to get your total load. If a device only shows VA, multiply by 0.7 to get an approximate watt figure. Add at least 20-25% buffer above your total load when selecting a UPS. This protects against inrush current on startup and leaves room for minor future additions without replacing the unit.

Step 3: Determine the Runtime You Need

Runtime is how long the UPS can power your equipment after mains fails. Ask yourself: do you need 5 minutes to save work and shut down cleanly, or 30 minutes to keep operating through short outages? Runtime reduces as load increases. Most UPS product pages show a runtime chart. Calculate your actual load first, then check the runtime curve at that load, not the headline maximum figure.

Step 4: Choose Your Topology

Use the topology table above. For most commercial and trade installations, line interactive is the right choice. Standby for low-budget residential or basic networking. On-line for anything mission-critical.

Step 5: Check Waveform Output

See the section below. If in doubt, specify pure sine wave.

Understanding VA vs Watts

VA (Volt-Amperes) and Watts are both used to rate UPS capacity and they are not the same number. This is the most common source of confusion when sizing a UPS.

Watts measures real power, the actual energy consumed. VA measures apparent power, which includes reactive current that does no useful work but still flows through the circuit. The ratio between the two is called the power factor.

The practical rule: multiply the VA rating by 0.6 to get the usable watt capacity of most UPS units.

So a 1000VA UPS typically delivers 600W of usable power. A 1500VA unit typically delivers 900W. Always size your UPS based on Watts, not VA alone. If the UPS specification only shows VA, divide by 0.6 to estimate maximum continuous watt capacity, or check the manufacturer's spec sheet for the actual watt rating.

Premium line interactive and on-line UPS units from Powercom have power factors of 0.9 or higher, delivering 900W from a 1000VA unit. Always check the spec sheet rather than assuming.

Pure Sine Wave vs Simulated Sine Wave

This is a critical specification for modern equipment and is frequently overlooked.

Pure sine wave: The UPS output when on battery is a smooth, perfect wave identical to mains power. Required by all modern Active PFC power supplies.

Simulated (stepped) sine wave: The UPS output when on battery is an approximation of a sine wave using stepped voltage levels. Adequate for simple resistive loads but incompatible with Active PFC power supplies.

Why this matters in practice: Virtually every modern computer power supply (including all Apple Macs, most current Windows PCs, servers, NAS devices, and high-efficiency commercial equipment) uses an Active PFC (Power Factor Correction) power supply. These require a pure sine wave input. When a simulated sine wave UPS switches to battery and feeds a stepped wave to an Active PFC supply, the supply may shut down immediately, cycle on and off, or fail silently, defeating the entire purpose of having a UPS.

Rule of thumb: If you are protecting any modern computer, server, Mac, NAS, or commercial IT equipment, always specify a UPS with pure sine wave output. All Powercom line interactive and on-line units in our range deliver pure sine wave output on battery.

Browse our full range: Line Interactive UPS | On-Line UPS

Battery Technology and Replacement

VRLA (Valve-Regulated Lead-Acid)

The vast majority of UPS units use VRLA sealed lead-acid batteries. They are maintenance-free, safe for indoor use, and cost-effective. Expected lifespan is 3 to 5 years under normal operating conditions (20-25°C ambient, regular charge/discharge cycles). High ambient temperatures significantly shorten battery life: every 10°C above 25°C roughly halves the expected battery service life.

Lithium-Ion

Higher-end UPS units increasingly offer lithium-ion battery options. Li-ion batteries last significantly longer (8-10 years), are lighter, charge faster, and tolerate higher ambient temperatures better than VRLA. The upfront cost is higher but total lifecycle cost is often lower when battery replacement and downtime are factored in. For installations where replacement is difficult or disruptive, Li-ion is worth specifying.

When to Replace the Battery

Signs that a VRLA UPS battery needs replacement:

  • The UPS alarms repeatedly or shows a battery fault indicator
  • Runtime has dropped significantly from when the unit was new
  • The battery is more than 4 years old
  • The unit was stored or operated in a hot environment
  • The UPS failed to hold load during a recent outage

Replacing the battery in a UPS is far cheaper than replacing the unit. Most Powercom units use standard cartridge batteries that can be hot-swapped without powering down connected equipment. Contact our team for replacement battery advice specific to your model.

NBN, Modems and Network Equipment

Protecting NBN equipment and networking gear is now one of the most common UPS use cases in both residential and light commercial installations. Since NBN does not provide battery backup on most connection types, a power outage means loss of internet and phone services until mains is restored, unless the equipment is on a UPS.

What to Protect

  • NBN connection device (NTD or modem): The NBN network termination device at the premises. Without power, no NBN connection regardless of what else is running.
  • Router / Wi-Fi gateway: Distributes the connection to devices. Needs to stay powered alongside the NBN device.
  • Managed switch (if fitted): Any switching equipment between the NBN device and the rest of the network.
  • VoIP adaptor (if fitted): For premises using VoIP phone services over the NBN connection.

What Size UPS for NBN and Network Equipment?

Network equipment draws surprisingly little power. A typical NBN modem draws 10-20W. A Wi-Fi router draws 10-25W. A small managed switch draws 15-30W. A combined load of 50-80W is typical for a home or small office network closet.

Installation Type Typical Load Recommended UPS Approximate Runtime
NBN modem + router only 30–50W 650VA standby 60–90 minutes
NBN modem + router + small switch 50–80W 1000VA line interactive 45–70 minutes
Small office network closet (modem, router, managed switch, patch panel gear) 100–200W 1500VA line interactive 30–60 minutes
Commercial comms room (firewall, core switch, multiple APs, servers) 300–600W+ 2000VA+ line interactive or on-line Varies by model, check runtime curve

For NBN and network equipment specifically, a line interactive UPS is strongly preferred over a basic standby unit. Brownouts are common on long distribution runs and in areas with older infrastructure, and a standby UPS switches to battery for every brownout, draining the battery and shortening its life. A line interactive UPS handles brownouts with its AVR without touching the battery at all.

Browse our Line Interactive UPS range or Standby UPS range.

Rack and Server Room Installations

For rack environments, several additional considerations apply beyond the standard selection process.

IEC Outlet Configuration

Rack UPS units typically output via IEC C13 outlets (for standard 10A equipment) and IEC C19 outlets (for high-current servers and PDUs). Confirm the outlet configuration on any rack UPS against the inlet types on your equipment before specifying. A UPS with only C13 outputs cannot directly supply C20-inlet servers without an adaptor cord.

Locking IEC Power Cords

In rack environments, standard IEC cords rely on friction alone to stay connected. During cable dressing, equipment moves, and maintenance, cords can be pulled free accidentally, causing immediate downtime. Specifying locking IEC C13/C14 cords between the UPS or PDU and connected equipment eliminates this risk entirely. Locking cords are fully compatible with standard C14 inlets and require only a deliberate squeeze-and-pull to disconnect.

This is particularly important for dual power supply servers where each PSU is on a separate power feed. Accidentally disconnecting the active feed instead of the failed one during maintenance is a common cause of avoidable outages.

Browse our IEC Locking Power Cords for C13/C14 and C19/C20 pairs.

Runtime and Extended Battery Modules

For server room and data centre applications where extended runtime is required, many rack UPS units support external battery modules (EBMs) that extend runtime significantly without replacing the UPS itself. If extended runtime may be a future requirement, check whether your chosen model supports EBMs before specifying.

Form Factor: Tower vs Rackmount

  • Tower: Freestanding unit designed to sit on a floor or shelf. The most common form factor for office, home, and small business use. Some tower UPS units can be converted to rackmount orientation with an optional kit.
  • Rackmount (1U, 2U, 3U): Designed to mount in a standard 19-inch equipment rack or communications cabinet. The correct choice for any rack environment. Rackmount units keep the UPS adjacent to the equipment it protects, simplify cable management, and allow the system to be secured in a locked cabinet.

Frequently Asked Questions

What is the difference between VA and Watts on a UPS?

VA (Volt-Amperes) is the apparent power rating. Watts is the real power capacity. The ratio between them is the power factor. For most UPS units, the usable watt capacity is 60% of the VA rating. A 1000VA UPS typically delivers 600W. Always size a UPS based on the actual Watt load of your equipment, not VA alone. Some premium units have a 0.9 power factor delivering 900W per 1000VA.

Do I need pure sine wave output?

Yes, if you are protecting any modern computer, server, Mac, NAS, or commercial IT equipment. All of these use Active PFC power supplies that require a pure sine wave input on battery. A simulated sine wave UPS may cause these power supplies to shut down immediately when the UPS switches to battery. All Powercom line interactive and on-line UPS units in our range provide pure sine wave output.

How long will a UPS run during a blackout?

Runtime depends on two things: the UPS battery capacity and the actual load connected to it. A lower load means longer runtime. Always check the runtime curve on the UPS specification sheet at your actual calculated load, not the headline maximum figure. As a practical guide, a 1000VA line interactive UPS powering 200W of network equipment typically delivers 30-45 minutes of runtime.

How often should I replace the UPS battery?

VRLA lead-acid batteries in UPS units typically last 3-5 years under normal operating conditions (20-25°C ambient temperature). In warmer environments, expect shorter battery life. Most UPS units will alarm when the battery needs replacement. Replacing the battery is significantly cheaper than replacing the entire unit. Contact our team for replacement battery advice for your specific Powercom model.

What UPS do I need for NBN and my modem?

For a basic NBN modem and router, a 650VA standby UPS provides 60-90 minutes of runtime at typical network equipment loads. For a small office setup with a modem, router, and managed switch, a 1000VA line interactive is the better choice as it also handles brownouts without switching to battery. See the NBN and Network Equipment section above for a full breakdown by installation type.

Can I use a UPS with a generator?

Yes, but the UPS topology matters. Standby and line interactive UPS units may struggle with the frequency and voltage variations that generator output produces, particularly when the generator is under varying load. An on-line double conversion UPS is the correct choice for generator-backed installations because it fully isolates the connected equipment from the generator output, regenerating a perfect clean supply regardless of input quality.

What is the difference between line interactive and standby UPS?

A standby UPS monitors mains power and switches to battery only when it detects a major problem like a blackout or large surge. A line interactive UPS adds an Automatic Voltage Regulator (AVR) that handles brownouts and over-voltage by boosting or trimming the voltage without drawing on the battery at all. For commercial applications and any installation on a long distribution run or in an area prone to voltage variation, line interactive is strongly preferred.

Your Project, Perfected. That's The Access Advantage.

  • Expert Local Support, Since 1973: Don't waste time with guesswork. Our experts have seen it all and are ready to provide the right solution, right now. Your success is our business.
  • Uncompromising Aussie Quality: We live and breathe quality. From rigorous testing to official Australian certification, we guarantee every product we sell is built to perform and built to last.
  • Your Specs, Your Brand, Our Build: Off-the-shelf not cutting it? We specialise in building custom cables and assemblies to your exact specifications, branded for your business. Let's create it together.
  • Guaranteed for Life: Buy it once. Trust it forever. Our products are backed by a limited lifetime warranty, so you can invest in quality with zero risk. *Warranty excludes third-party brands such as HALO and UPS.
  • Innovation That Keeps You Ahead: To ensure you always have access to the latest, most reliable solutions on the market, our catalogue is always changing with the tech landscape.

Let's get your project started.
Talk to an expert today for a custom quote or browse the solutions most relevant to your search.

Shop All UPS Ask an Expert Call Us