Which systems commonly rely on UPS backup?

Data-centre servers, equipment in server rooms and telecommunications facilities are common examples of loads where continuity matters. Servers may host applications or store data; network equipment connects users and systems; telecommunications equipment supports communications. If power to these systems is interrupted, dependent services may also be affected. Not every device in a rack or facility needs the same level of backup. Identify which equipment must keep operating or shut down in a controlled way, then separate it from devices that can tolerate losing power. This helps focus UPS capacity on the loads that matter most to operational continuity.

What is an uninterruptible power supply and what does it do?

An uninterruptible power supply (UPS) uses stored energy to keep connected devices powered when their normal supply is disrupted. It can help maintain continuity for loads such as a server and the network switch it relies on. The specific benefit depends on the UPS design and what’s connected. Plan which devices need support together, including any equipment required for them to function.

How long can an uninterruptible power supply run equipment?

There’s no single runtime that applies to every installation. The time available depends on the UPS configuration, battery condition and load at the time of an outage. Define the action the battery window must support, then use the unit’s documentation for the relevant load. Reassess runtime as equipment changes, since adding devices can reduce the available backup period.

What is the difference between a UPS and a surge protector?

A UPS can use stored energy to keep connected equipment operating during a supply interruption; a surge protector is intended to limit the effect of voltage spikes and doesn’t provide outage backup by itself. For example, a workstation connected only to surge protection will lose power during an outage. Treat surge protection and battery backup as separate functions, and review each device’s documented capabilities.

Can a UPS keep servers running during a power outage?

Yes, a UPS can keep a server running during an outage if the connected load is within its rated output and the system has sufficient battery capacity for the required period. Include dependencies such as network switches or storage equipment if the server needs them to maintain a service. Decide whether the goal is temporary operation or a controlled shutdown, then plan the protected load accordingly.

What does UPS output power factor mean?

Output power factor describes the relationship between a UPS’s real-power capacity in watts and its apparent-power capacity in volt-amperes (VA). It indicates how much of the VA rating is available as usable real power. Equipment with a stated watt demand must stay within the UPS’s watt rating, even if its VA rating appears sufficient. Compare both output ratings with the connected equipment’s requirements.

Is a UPS the same as a generator?

No. A UPS stores energy for short-term backup, while a generator creates electrical power and is generally used to support longer outages. A site may plan them as separate layers, with the UPS supporting selected equipment while a generator starts. The two systems have different roles and need a co-ordinated design. A UPS alone shouldn’t be treated as an indefinite source of power.

How do I know what size UPS my equipment needs?

Start by listing the equipment to be protected and recording each device’s documented power demand in watts and VA, where provided. Separate essential loads from equipment that can be disconnected, then consider how the system may grow. Compare the combined requirements with both UPS output ratings and the planned operating response. Detailed sizing should account for the actual configuration, not just the total printed on equipment labels.

Uninterruptible Power Supply: Guide for Critical Systems

UPS Power Systems

Jayden Currie

October 12, 2026

10 minutes

Online vs line-interactive UPS: what critical systems actually need | RackPower

Online vs line-interactive UPS: what critical systems actually need

Not every rack needs the same UPS. A UPS for a reception PC and one for a hospital's core switches solve different problems. The first decision is the type of UPS. The second is what you build around it so a single fault can't take the rack down.

Line-interactive vs online double conversion

	Line-interactive	True online (double conversion)
How it works	Passes mains through, corrects voltage, switches to battery when mains fails	Converts all incoming power to DC and back to clean AC, all the time
Transfer to battery	A few milliseconds	Zero; the inverter is always running
Output quality	Mains, corrected	Clean sine wave regardless of input
Handles generator power	Can struggle with frequency drift	Yes
Best for	Desktops, small network cabinets, non-critical gear	Servers, storage, telco, control systems, anything on a generator
RackPower range	Line-interactive UPS	Rack and tower online UPS, 1–10 kVA

The old argument against online UPS was efficiency: running the inverter constantly wasted power as heat. RackPower's online units run at up to 96% efficiency (1–3 kVA) and 95% (6–10 kVA), which closes most of that gap.

Which type do you need?

Answer three quick questions.

Would an unexpected shutdown of this equipment stop the business or a service? Yes No

Is there a generator, or a rural or unreliable supply? Yes No

Does the rack hold servers, storage, telco or control equipment? Yes No

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Remove the single points of failure

A UPS protects against mains failure. It can also become the thing that fails. For a critical rack, plan around that:

Maintenance bypass. A UPS bypass switch lets you take the UPS out of circuit for service or battery replacement while the rack stays on mains. Without one, battery replacement means a shutdown.
Dual power paths. Servers with two power supplies should be fed from two separate sources, A and B, ideally on separate UPS units or one UPS and one mains feed. Never plug both supplies into the same power board.
Single-corded equipment. Switches and firewalls with one power supply can still get dual-path protection through an automatic transfer switch, which flips to the second feed if the first fails.

A typical A/B layout. Each dual-corded server takes one supply from each PDU; single-corded gear gets a second path through an automatic transfer switch (ATS).

Know when something is wrong

A UPS on battery at 2 a.m. is no use if nobody knows. For critical systems:

Fit the UPS's optional network management (SNMP) card and connect it to your monitoring system, so on-battery and low-battery alerts reach someone by email or text.
Configure automatic shutdown for servers that must close cleanly, and test that it actually triggers.
Use metered PDUs to watch load per rack, so you see creeping load before it overloads the UPS.

Maintain it like it matters

UPS batteries wear out. Sealed lead-acid batteries typically last 3–5 years, less in hot rooms. Test runtime once a year, record the result, and replace batteries before the test shows a big drop, not after an outage reveals it. Keep the room or cabinet ventilated; heat is the biggest single cause of short battery life.

Replacement batteries: RackPower can supply replacement battery sets for our UPS range and advise on swapping them over. Have your UPS model and purchase date handy when you get in touch.

Designing a critical rack?

RackPower designs and manufactures PDUs and distribution boards in New Zealand and supplies the UPS, bypass and transfer switches that go with them, so the whole power chain can be specified together.

Contact RackPower Call 0800 452 140

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