Why NBN VOIP Goes Down When the Power Does
Old copper telephone lines (PSTN) carried their own low-voltage power through the cable itself. Your handset worked during a blackout because it drew power from the exchange, not from your mains supply. That is gone. When Australia rolled out the NBN, the copper network was progressively shut down. VOIP runs entirely over your internet connection, and your internet connection runs over hardware that plugs into the wall.The consequence is straightforward: no mains power means no internet, which means no VOIP. For a residential user this is inconvenient. For a business, it means missed inbound calls, no ability to contact customers, and no way to call staff. The 2-hour power cut nobody noticed until they checked their missed calls log is a real and common scenario.What Needs Power in an NBN VOIP Setup
To keep your VOIP phones working during a power outage, every device in the chain must stay powered. The exact equipment depends on your NBN connection type, but for most business setups the stack looks like this.The Optical Network Terminal or Network Termination Device (FTTP and HFC)
If you have FTTP (Fibre to the Premises) or HFC (Hybrid Fibre Coaxial), NBN Co installs a box at your premises: an ONT (Optical Network Terminal) on FTTP, or an NTD (Network Termination Device) on HFC. This box converts the NBN signal into an Ethernet connection your router can use. It runs on mains power and is the first device that dies when the power goes out. Without it, your internet connection is gone regardless of what else is running.Your Router or Modem
The second device in the chain is your router. Even if the ONT or NTD stayed alive, a dead router means no network, which means no VOIP. This applies regardless of your NBN connection type.Your VOIP ATA, IP Desk Phones, and PoE Switch
If you use a standalone ATA (Analog Telephone Adapter) to connect traditional handsets to your VOIP service, that device needs power too. If you use IP desk phones that run over PoE (Power over Ethernet), the PoE switch or injector that powers them must also stay running. Some IP phones have their own power adapters; check your equipment. The point is that every device in the path from the wall to your handset must have power.What About FTTN and FTTC?
FTTN (Fibre to the Node) and FTTC (Fibre to the Curb) connections use the existing copper network for part of the run, and the node or curb equipment is powered by NBN Co, not your premises. So the signal from the street to your router may survive a local outage. However, your router still needs mains power to work, and your VOIP equipment still needs mains power. In practice, FTTN and FTTC users have the same problem: no mains power at your premises means no VOIP calls.NBN Co's Battery Backup Unit: What It Is and What It Covers
When NBN rolled out, there was a recognised problem: FTTP customers who relied on a home phone for emergencies would lose all phone access during a power cut. NBN Co developed a Battery Backup Unit (BBU), a small uninterruptible power supply designed to keep the ONT running for up to 5 hours during an outage. These were provided free to customers classified as 'vulnerable' (typically medically dependent or living alone).The BBU program has significant limitations that matter for business users. First, it only covers the ONT on FTTP connections. It does not power your router, your VOIP ATA, your IP phones, or your PoE switch. So even with a BBU installed, your VOIP phone system goes down when the power does unless you separately protect the rest of your equipment. Second, the free provision program ended for most new connections. Replacement batteries and new units may be available from some RSPs (retail service providers) but availability and cost vary. Third, it is only relevant to FTTP connections. HFC, FTTN, and FTTC customers do not have a BBU option.
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The NBN Co BBU only protects the ONT (FTTP only). It does not protect your router, VOIP ATA, or phones. A business relying on the BBU alone will still lose VOIP during a power cut.
Practical Protection Options for Business VOIP
Option 1: UPS (Uninterruptible Power Supply)
A UPS is the most reliable and practical solution for any business that relies on VOIP as its primary phone system. A UPS connects between your mains supply and your networking equipment. When power fails, the battery takes over instantly, with no interruption to your devices.For a standard NBN VOIP setup (ONT or NTD, router, VOIP ATA or IP phone), a small to mid-range UPS will provide 1 to 4 hours of runtime depending on the load and battery capacity. Most short outages in Australian metropolitan areas resolve within 2 hours. A UPS covers the vast majority of real-world outage scenarios.What to plug into your UPS: the ONT or NTD (if FTTP or HFC), the router, the VOIP ATA or IP phone power supplies, and the PoE switch if you use one. Do not plug in PCs, monitors, or other high-draw equipment unless you are specifically sizing the UPS for that load. Keeping only the network and phone stack on the UPS maximises runtime.Cost: a business-suitable UPS with enough runtime for a small networking stack typically runs from around $150 to $400 AUD depending on battery capacity and brand. APC, CyberPower, and Eaton all have units in this range available through Australian IT retailers and Amazon AU. Check current pricing as stock and models change. For a business losing even one inbound call per month during outages, a $200 UPS pays for itself quickly.A UPS is not complicated. Buy one with VA capacity appropriate for your stack, plug in the devices you need to protect, and set it aside. This is the same category of cheap insurance as taking out cloud VOIP in the first place.Option 2: Mobile App Fallback
Most cloud VOIP providers (including Maxotel and others serving the Australian market) include a softphone app for iOS and Android. If your NBN VOIP goes down, you can receive and make calls via the same business number on your mobile phone, using your mobile data connection.This is a zero-cost layer of protection that most businesses with a cloud VOIP service already have available. The setup requires installing the app, logging in with your VOIP credentials, and confirming it works before you need it. The limitation is that mobile data must be available at your location. In most Australian metropolitan and regional areas this is reliable. In remote areas, mobile coverage may be the constraint.Mobile app fallback does not require a UPS or any additional hardware. It should be configured as a standard part of your VOIP setup, not as an afterthought. Check with your VOIP provider that the mobile app is included in your plan.Option 3: 4G or 5G Failover Router
For businesses where phone downtime is genuinely costly (inbound sales lines, emergency services, medical receptions), a cellular failover router provides a more complete solution. These routers maintain a 4G or 5G SIM connection alongside the NBN WAN connection and automatically switch to cellular if the NBN link drops. Your VOIP phones continue working because the internet connection itself stays up.This requires a router with cellular failover capability and an active SIM with a data plan. For most small businesses it is more than needed. For high-volume or emergency-service businesses, the ongoing SIM cost is justified.Note that a cellular failover router only addresses internet connectivity. If your mains power is out, your router (including the failover router) still needs power. A UPS combined with a failover router gives protection against both NBN outages and power outages.000 Emergency Calling During a Power Outage
This is the most important section in this article. Read it before anything else if you rely on VOIP as your only phone.
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Under the old copper network, triple zero calling was available even during power outages because the line carried its own power. That guarantee does not exist with VOIP. If your VOIP setup loses power, calling 000 is not possible through your VOIP phone.The ACMA (Australian Communications and Media Authority) has published guidance on this issue, noting that VOIP services do not provide the same 000 accessibility as traditional telephone services during power failures. Providers are required to inform customers of this limitation.The practical requirement is simple: if VOIP is your only landline service, keep a charged mobile phone available at all times that can call 000 independently of your internet connection. Mobile networks have their own power backup at the tower level and will typically remain operational during a local power outage.For more detail on VOIP and 000 calling including what your provider is required to tell you, see our full guide at /guides/000-emergency-calling-voip-australia/.VOIP cannot call 000 when your power is out and your VOIP equipment is not backed up. If someone at your premises has a medical emergency during a power outage and your VOIP phone is the only phone, you may not be able to call for help. Always have a charged mobile phone available as a backup for 000 calls.
Vulnerable Users and Medical Alarms
If someone at your premises relies on a monitored medical alarm, personal duress alarm, or monitored fire alarm that connects via the phone line, power outage resilience is a serious concern that goes beyond VOIP availability.Many older medical and personal alarms were designed for the copper telephone network and may not operate correctly over VOIP at all, regardless of whether the power is on. On top of that, a power outage removes the phone connectivity that the alarm uses to call the monitoring centre.If you are managing a premises with a phone-based medical or duress alarm, consult the alarm provider directly before switching to VOIP. The solution may require a cellular-connected alarm unit that operates independently of the premises internet and phone connection. This topic is outside the scope of this guide but is important enough to raise explicitly.Australian Context: NBN Co Guidance and Consumer Rights
NBN Co publishes guidance for consumers on battery backup and power resiliency. The NBN Co website includes information on the BBU program and power supply requirements for different connection types. Your retail service provider (the company you pay for your internet service) is required under ACMA regulations to disclose that VOIP does not guarantee 000 access during a power failure before you move to an NBN VOIP service.Under Australian Consumer Law, if a provider fails to make this disclosure and you suffer a loss as a result, you may have grounds for a complaint through the Telecommunications Industry Ombudsman (TIO). The TIO handles disputes between consumers and telco providers and is free to use.In practice, most providers now include the 000 power failure disclosure in their signup paperwork, but it is often buried. The practical answer is to not rely on a single disclosure. Understand the limitation yourself, put a UPS in place, and keep a charged mobile available.Common Mistakes Businesses Make with NBN Battery Backup
Most businesses do not think about power backup for their phone system until a power cut happens and they miss calls. Here are the three mistakes that make that situation worse.Mistake 1: Assuming the NBN BBU Covers Everything
Some FTTP customers know they have a Battery Backup Unit installed on their ONT and assume their VOIP is protected. It is not. The BBU keeps the ONT running, but your router and VOIP equipment are still dead. If you have a BBU installed, verify whether your router and VOIP stack also have backup power. They almost certainly do not unless you put a UPS in place yourself.Mistake 2: Not Configuring the Mobile App Before Needing It
Almost every cloud VOIP service includes a mobile softphone app. Most businesses never install it until their VOIP goes down and they urgently need it. By then, it is too late to configure credentials, test the connection, and verify it works on mobile data. Install and test the mobile app when you set up your VOIP service. Confirm calls route to it correctly. Then set it aside and forget it until you need it.Mistake 3: Forgetting the PoE Switch
Businesses that upgrade to proper IP desk phones often have a PoE switch powering the phones. When they buy a UPS, they plug in the ONT, router, and ATA but forget the PoE switch. The phones go dark in an outage because the switch is not protected. Map out every device in your communications chain before buying a UPS, and make sure the UPS is sized to cover all of them.Your Next Steps
Use this checklist to assess and improve your business phone resilience. 1. Map your equipment. Every device from the wall to your handset: ONT or NTD, router, VOIP ATA or IP phone power supplies, PoE switch if applicable. 2. Check what is already backed up. Do you have a BBU on your ONT? For most businesses, nothing is backed up. 3. Buy a UPS sized for your stack. Add up the watt draw of all networking and VOIP devices, then buy a UPS with VA capacity well above that total. 4. Install and test your VOIP provider's mobile app on mobile data before you need it. 5. Confirm you have a charged mobile available for 000 calls at all times. 6. If you have a medical alarm or monitored duress device, contact the alarm provider about power outage behaviour before switching to VOIP.If you're still deciding whether VOIP is right for your business, our guide to VOIP vs traditional phone covers the core differences worth understanding before you commit.Not sure if your current phone setup is protected during an outage? Get a personalised recommendation for your business, including advice on VOIP resilience and backup options.
Get a RecommendationDoes NBN VOIP work during a power outage?
No. NBN VOIP requires mains power at every device in the chain: the ONT or NTD (FTTP and HFC), your router, and your VOIP equipment. When mains power fails, all of these go offline unless they are connected to a UPS. The old copper telephone network had its own power supply through the cable, but NBN VOIP does not.
What is the NBN Co Battery Backup Unit and who can get one?
The NBN Co Battery Backup Unit (BBU) is a small UPS designed to keep the ONT running on FTTP connections during a power outage, providing approximately 5 hours of backup. It was originally provided free to vulnerable customers during the NBN rollout. Free provision has largely ended for new connections. The BBU only covers the ONT; your router and VOIP equipment remain unprotected. Contact your retail service provider if you believe you qualify for a BBU or need information about replacement batteries.
Can I call 000 during a power outage on a VOIP phone?
Not unless your VOIP equipment is backed up by a UPS and your internet connection is still active. VOIP cannot call 000 when the equipment is unpowered. The ACMA requires providers to disclose this limitation. The backup solution is a charged mobile phone, which can call 000 via the mobile network independently of your internet connection.
What size UPS do I need for my VOIP setup?
For most small business VOIP setups (ONT or NTD, router, ATA or IP phone power supplies), a 500VA to 1000VA UPS will provide 1 to 3 hours of runtime. Check the watt draw on each device and buy a UPS with VA capacity roughly double the total watt draw. This gives headroom and extends battery life. Budget from around $150 to $400 AUD for a suitable unit from brands like APC, CyberPower, or Eaton available through Australian IT retailers.
Does FTTN or FTTC have better power backup than FTTP?
The node and curb equipment in FTTN and FTTC is powered by NBN Co and has its own backup power, so the signal from the street may survive a local outage. However, your router and VOIP equipment at your premises still require mains power. In practice, FTTN and FTTC business users face the same problem as FTTP users: no mains power at your premises means no VOIP calls without a UPS in place.
Can I use a mobile softphone app as backup if my VOIP goes down?
Yes. Most cloud VOIP providers include a mobile softphone app that routes calls through your business number over mobile data. If your NBN VOIP goes down due to a power cut or internet outage, the app allows you to continue receiving and making calls on your mobile. The key is to install, configure, and test the app before you need it. Trying to set it up during an actual outage is not practical.
Does a medical alarm still work on VOIP during a power outage?
Not reliably. Many older medical and personal alarms were designed for the copper telephone network and may not function correctly over VOIP under any conditions. A power outage removes the phone connectivity entirely. If someone at your premises relies on a phone-based medical alarm, consult the alarm provider directly before switching to VOIP, and ask specifically about power outage scenarios. A cellular-connected alarm unit may be required.
What happens to inbound calls during a VOIP outage?
This depends on how your VOIP service is configured. Cloud VOIP services typically have failover options: calls can be forwarded to a mobile number, routed to voicemail, or handled by an auto-attendant message. The service itself continues running in the cloud; it is your premises equipment that is offline. Configure your inbound call routing failover settings before an outage, not during one. Check your VOIP provider's portal for failover and voicemail settings.