How to Keep Fibre Internet Running in a Power Cut: UPS Guide for ONT and WiFi

The short answer: back up both the ONT and router

For a typical fibre installation, the optical network terminal, or ONT, and the WiFi router both need power. A UPS connected only to the router leaves a gap if the ONT loses electricity. If your connection also uses a powered switch, access point or mesh unit, decide which of those devices must remain running for the service you want during an outage.

A UPS can preserve power to your equipment for a limited period. It cannot guarantee that the provider's network, an upstream connection or another external service remains available. Think of it as one part of an outage plan. Keep a charged phone and another communication option where continuity matters, especially if you depend on an internet-based telephone service.

Map the entire connection before choosing equipment

Locate the ONT and its power supply. Trace the Ethernet cable to the router, then identify any switch, mesh main unit or other powered device along the path. Label the relevant plugs so somebody else in the household can recognise the equipment without unplugging it experimentally.

The location of each component affects the purchase. If the ONT is in a garage and the router is upstairs, one UPS beside the router may not cover both. You might need backup at two locations or a professionally planned change to the layout. Do not run loose extension leads across doors or walkways as a permanent solution.

Write down what you actually want working: one WiFi zone, a work computer, a security-camera recorder or the whole home network. A modest goal requires less energy and fewer devices than trying to maintain every appliance. Put essential communications ahead of non-essential loads when planning limited battery capacity.

Fibre internet power backup: connection diagram

NZ installation tip: The ONT may be in a garage or utility cupboard while the router is elsewhere. A UPS only protects equipment plugged into its battery-backed outlets. If the equipment is far apart, plan two appropriately sized backup units rather than unsafe extension-lead runs.

Watts, VA and energy: three different questions

Watts describe the real power the connected equipment uses. VA is another output rating relevant to the UPS's electrical capacity. Battery energy and the manufacturer's runtime data determine how long the supported load may run. A 1000VA label is not a statement that the unit provides 1000 watt-hours of stored energy.

Check both the watt and VA limits for your selected UPS. A lightly loaded router setup may sit well below those limits, yet runtime can still vary with battery condition, conversion losses and the UPS's own consumption. A higher output rating does not automatically produce proportionally longer runtime for a small load.

Power-adapter labels are useful for identifying electrical requirements, but their maximum output is not the same as the device's measured continuous consumption. If practical, measure the total load with an appropriate meter or use supported manufacturer figures. Include every device you plan to leave connected.

Estimating runtime without making a false promise

Start with an illustrative load budget. If an ONT uses 10W and a router uses 15W, the combined example is 25W. Those numbers are assumptions, not measurements of your equipment. Add a switch or access point and the total changes. Always replace the example with your actual setup before choosing a battery size.

Where the manufacturer provides a runtime curve for the exact UPS, use it at the expected load. That is more useful than dividing an unexplained battery figure by watts. Lead-acid battery behaviour, inverter losses, low-load shutdown and age can make a simple calculation optimistic.

Use the TSS UPS runtime calculator as a planning aid, then confirm the result against the manufacturer's data and an outage test. Its inputs and assumptions should remain visible. Do not describe a calculated estimate as a guarantee, particularly for a service that must stay available for work, alarms or telephone access.

Worked load comparison: 25W versus 40W

These are example electrical loads, not measured figures or promised backup durations. For illustration, if a manufacturer's verified chart shows 90 minutes at 25W and 55 minutes at 40W for a particular unit, those are the figures to compare for that unit only. Do not assume those illustrative durations apply to the DIGITUS UPS models linked below. Some manufacturers do not publish low-load data, in which case ask the supplier for measured figures or test the fully charged system in accordance with the manual.

Record the UPS model, battery age, connected load in watts, desired outage duration and result of a supervised power-loss test. Actual operating time changes with battery condition, temperature, UPS self-consumption and equipment demand.

Compare the main options

Selecting a UPS for the actual installation

Compare these relevant TSS products using the current specifications on their pages: Digitus Line Interactive UPS 1000VA 600W (DN-170074-NZ), Digitus Line Interactive UPS 1500VA/900W (DN-170075-NZ), Digitus Line Interactive UPS 2000VA 1200W (DN-170076-NZ). Availability and fulfilment details can change; confirm them before ordering.

The Digitus DN-170074-NZ and DN-170075-NZ are line-interactive UPS examples available through TSS. Their output ratings are different, but that alone is not enough to establish the runtime of a particular fibre setup. Check the exact NZ outlet arrangement, battery details and manufacturer's instructions before deciding which fits.

An AC UPS usually allows you to keep the ONT and router's original power adapters, which simplifies voltage compatibility. A DC backup unit needs more careful matching. The connector may physically fit while the voltage or polarity is wrong. Never substitute a power supply based only on the appearance of its plug.

Consider alarms, ventilation, battery replacement and physical space. A unit in a bedroom might be inconvenient if it beeps repeatedly during an outage. A cupboard needs the clearances required by the manufacturer. Keep the UPS dry and accessible rather than concealing it where heat builds up or the battery cannot be inspected.

NZ internet calling and emergency communications

Some New Zealand landline calling services use broadband rather than traditional exchange-powered copper. During a power cut, a phone service supplied through the fibre router or an additional voice adapter may stop working unless every required powered component has suitable backup. Even with a UPS, internet and phone service can be interrupted by wider network faults. Ask your internet or phone provider what equipment needs battery backup and whether its calling service remains supported during an outage.

Do not rely on an untested fibre landline as your only way to call 111 during a blackout. Keep a charged mobile phone and a suitable alternative plan, recognising that mobile coverage and local cell sites can also be affected by prolonged outages. If emergency calling is essential to your household, discuss continuity arrangements with your provider.

Commissioning: test while everything is working normally

Fully charge the UPS as directed before testing. Connect the essential equipment to backed-up outlets, distinguishing them from surge-only outlets if the model has both. Confirm internet access and WiFi in the intended room before simulating an outage using the safe procedure in the UPS manual.

During the test, check whether the ONT remains powered, whether the router reboots and whether the service still works from a phone or laptop. A lit router is not proof of internet access. Record the test date and observed behaviour, then restore normal power and confirm charging resumes.

Do not repeatedly deep-discharge the battery simply to measure it every week. Follow the manufacturer's maintenance schedule. Replace batteries only with approved specifications and safe handling procedures. A UPS that worked when new can provide less runtime later, so periodic review matters as much as the original purchase.

Keep the outage plan realistic

For extended outages, decide which loads can be switched off and how you will conserve energy. A laptop's own battery may cover computing while the UPS supports the network. A second communication path can help if the fibre service itself fails, but it has its own coverage and power limitations.

For more planning tools, visit the TSS Tech Tools hub and its UPS runtime calculator. Choose equipment from measured needs, verified compatibility and a realistic target duration. The aim is a tested, understandable setup that your household can use confidently when the lights go out.

Frequently asked questions

Will a UPS guarantee fibre internet during a blackout?

No. It can keep your local equipment powered, but the provider network and other services must also remain operational. Retain another communication option when access is critical.

Do I need to back up the ONT as well as the router?

Usually yes for fibre. Both require power. Identify any other powered devices that sit in the path to the WiFi or wired connection you want to preserve.

Does 1000VA tell me the runtime?

No. It is an output-capacity rating, not stored energy. Check the manufacturer's runtime curve for the expected load and battery condition.

Can I use any DC backup battery with the ONT?

No. Voltage, current, polarity and connector must match the exact device. Keep the original adapter or use a documented compatible backup solution.

Plan your network backup with TSS

Browse TSS uninterruptible power supplies and compare the exact model details before you choose. For help matching equipment to your setup, contact Tech Supply Shed with your current model and requirements.

Sources and further reading

Technical references checked on 2 October 2026: DIGITUS UPS specifications; Chorus fibre and backup context