The Modest Blackout Kit: Right-Sizing a UPS for Fibre, Wi-Fi and a Small NAS

Start with what actually needs to stay up

A UPS is one of those purchases that looks simple until you're staring at a wall of VA ratings, IEC sockets and claims about 'pure sine wave' output. For a British home setup, the job is usually modest: keep the fibre ONT powered, keep the router broadcasting Wi-Fi, and give a small NAS enough time to ride out a short outage or shut down cleanly.

That is not the same as keeping the whole house running. You are not powering a kettle, a tumble dryer or a gaming PC mid-render. You are building a small, boring bubble of mains power around the bits that hold your connection and your data together. In 2026, with more of us working from home at least part of the week, that bubble is worth getting right.

VA is not watts, and watts are what matter

UPS boxes shout about VA, or volt-amperes. That is apparent power, and it is not the same as the watts your gear actually draws. A 600VA UPS might be rated for only 360W, and a 1000VA unit might top out around 600W. The watt figure is the one to watch because it reflects real load, especially with modern switch-mode power supplies.

For a fibre ONT, a router and a two-bay NAS, you are probably looking at somewhere between 40W and 100W at idle, depending on the NAS disks and how much the router is doing. That is well inside the comfort zone of a small UPS. The trap is buying by VA alone, then assuming a 1500VA unit will run your setup for hours. It won't if the battery is tiny and the load is higher than you measured.

The sine wave question

Cheap UPS units often produce a stepped or modified sine wave. For a basic router or ONT, that may be fine. For a NAS with an active power factor correction PSU, it is less lovely. Some power supplies buzz, run warmer or refuse to start on a rough waveform. If you are spending serious money on disks and want clean shutdowns, pure sine wave output is the safer choice.

You do not need laboratory-grade power. You need a UPS that will not make your NAS PSU unhappy at the exact moment you need it most. If the price difference is modest, go pure sine. If you are protecting a single router and an ONT, a decent stepped unit can still be acceptable, but check the manufacturer's guidance rather than assuming.

Measure the idle draw, not the label

The label on a router or NAS is a maximum, not a promise. A plug-in energy monitor is the honest way to find out what your kit really pulls. Put it inline for a day, note the idle figure and the peak when disks spin up, then add the ONT. Remember that a NAS can draw a surprising surge at startup, even if it sips power afterwards.

If you do not have a monitor, use the manufacturer's idle figures as a starting point and leave headroom. A 60W measured load is a comfortable target for a small UPS. A 150W load starts to demand a bigger battery if you genuinely want two hours. Be honest about the difference between 'ride out a 20-minute flicker' and 'keep working through a two-hour repair'.

UK plugs, leads and the extension-lead trap

Most small UPS units sold here have IEC C13 outlets, not UK three-pin sockets. That means you will need UK-to-IEC leads or adapters for your ONT, router and NAS. Buy proper leads rather than a nest of adapters. Keep the run short and avoid daisy-chaining extension leads off the UPS output. If the manufacturer says plug the UPS directly into a wall socket, do that rather than feeding it from a surge-protected strip.

Also think about where the UPS lives. Under a desk is fine if it has ventilation. In a closed cupboard next to a radiator is not. Batteries dislike heat, and a UPS that cooks quietly for three years will not give you the runtime you paid for. In a British flat, the hallway cupboard may seem tempting, but check the temperature and the cable route before you commit.

What two hours really looks like

Runtime is not a magic number. It depends on load, battery age, temperature and inverter efficiency. A small 600VA/360W UPS with a 12V 7Ah battery stores roughly 84Wh. At a 60W load and reasonable efficiency, that is around an hour, not two. A larger unit with two 7Ah batteries gives you more headroom, but it is still a small battery system.

If your goal is genuinely two hours for an ONT, router and NAS, aim for a UPS with a sensible watt-hour figure and keep the load lean. Disable the NAS's power-hungry extras, let disks spin down if that suits your setup, and set the NAS to shut down automatically after a set time on battery. The UPS should be a bridge to a clean shutdown, not a fantasy generator.

A sensible shopping list and setup

Look for a line-interactive UPS with a watt rating comfortably above your measured load, pure sine wave output if the budget allows, and enough outlets for your three core devices. A USB or network shutdown signal is valuable for the NAS. Test the setup before winter: pull the mains plug, watch what stays up, and confirm the NAS receives the shutdown command. Label the plugs so nobody swaps the router lead for a desk lamp.

And keep expectations grounded. A UPS is blackout insurance for your broadband and your data, not a whole-home backup. Sized properly, it will quietly do its job through the short cuts and winter flickers that would otherwise leave you rebooting everything and hoping the disks are fine.