What is NBN HFC (hybrid fibre coaxial)?

What HFC is

HFC stands for hybrid fibre coaxial. It is the type of NBN that uses fibre to bring the internet to your street, then the coaxial cable network that was built for pay TV to carry it into your home.

Coaxial cable, or coax, is the round cable with a single pin in the middle and a screw-on connector. If your home ever had cable pay TV or cable internet, that is the cable, and on HFC it is now your NBN line. When it plays up, the first question is which side of the NBN box the fault sits, which is what an independent NBN technician works out on site.

How HFC works

1. 1

   Fibre to your area

   Fibre runs from the NBN network to a node that serves your neighbourhood.

2. 2

   Coaxial cable along the street

   From the node, the pay TV cable runs along the street, overhead on the poles or underground, with a tap near each group of homes.

3. 3

   The lead-in to your home

   A coaxial cable runs from the tap to your home, through an isolator, to a wall plate inside.

4. 4

   The HFC box on the wall plate

   NBN's HFC box screws onto the wall plate with a short coaxial lead. Your router plugs into the box with a network cable and makes the WiFi.

One HFC street, from above

Show the street

Morning Evening Damaged isolator

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1. 1Fibre node
2. 2Shared coaxial cable
3. 3Isolator
4. 4HFC box
5. 5How busy the shared line is

Why NBN used HFC instead of fibre to the premises

Because the cable was already there. Running new fibre into every home takes years and costs a great deal. In suburbs where the pay TV cable already passed every house, using it meant homes could be connected sooner and for less.

It was a reasonable trade. Coaxial cable was built to carry a lot of signal, so HFC can take much faster plans than the types that finish on an old phone line.

The HFC box

The HFC box is NBN’s connection device for this type of service: a small box, black or white, with four lights down the front and a round screw-on connector at the back. It belongs to NBN and stays with the property. You might hear it called the HFC modem or the NBN box.

There are two HFC boxes in homes now, the Arris CM8200 and the newer Arris CM3500, and both carry the same four lights. When all four are steady green, it is connected. For what each light means, and what flashing lights are telling you, see the HFC connection box lights.

Two things to know about it:

• It is the modem. Your own router plugs into it. You do not need a second modem.
• It stays where the wall plate is. The box has to sit on the coaxial wall plate, and that plate is often wherever the pay TV used to be. If that is a poor spot for WiFi, the box can be moved or a cable run from it to a better place for the router. See NBN box relocation.

The HFC isolator

The isolator is a small metal fitting, about the size of a thumb, screwed in line with the coaxial cable where it comes into your home. Its job is to stop stray electrical current on the street cable reaching your equipment while letting the internet signal through.

The isolator belongs to NBN. It is part of their network, not part of your home’s cabling. Some homes still have an older one from the Foxtel days, because some HFC services run on cabling that was first put in for Foxtel and later taken over for the NBN. The old pay TV cabling inside the house, the outlets and splitters behind the TV, is ours to sort out as part of TV and Foxtel cabling at home; the isolator itself stays NBN’s.

Most people never notice it until it fails. A storm, a power surge or plain corrosion can damage it, and then the service drops out, slows down or stops, while the box itself is perfectly healthy.

What to do about a damaged isolator

You cannot ring NBN yourself about this. A damaged isolator is reported through your provider, and your provider asks NBN to attend.

Providers usually want proof before they will do that. This is how our technician proves it:

1. The isolator is taken out of the circuit.
2. The HFC box is connected straight to the lead-in cable.
3. The service is tested both ways. If it works without the isolator and fails with it, the isolator is the fault.

We then give you a report that says so, which you send to your provider, or we call your provider on your behalf.

Advantages of HFC

• Fast plans. HFC can take high speed plans that the copper types cannot.
• Distance matters little. Speed does not fall away with the length of the line the way it does on a phone line.
• Old phone wiring is out of the picture. The internet does not run through the phone sockets, so old sockets do not drag it down.

Disadvantages of HFC

• It is shared. Homes on the same stretch of cable share its capacity, so it can slow in the evening when the street is online.
• Fittings and splitters. Every connector on a coaxial cable is a place for corrosion or a loose thread. Old splitters left behind from a pay TV setup weaken the signal to the box.
• Weather. Water in a connector outside or at the tap shows up as dropouts when it rains. There is a job like that, on video, in how weather affects your phone and internet.
• Power. The HFC network needs power in the street as well as in your home, so an outage nearby can take your service down even when your own lights are on.

What goes wrong on HFC, and whose side it is

What you see on HFC, and where the cause usually sits

What you see	What it usually points to	Whose side
Downstream or upstream light keeps flashing	A weak signal reaching the box: a loose or corroded fitting, an old splitter, the isolator	Either side. It needs testing
Stopped after a storm or a power surge	The isolator, the box or its power supply	NBN's, reported through your provider
Drops out when it rains	Water in a connector, at the tap or along the lead-in	Usually the network side
Slow in the evening, fine in the morning	The street is busy, or your provider's own network is	Not your home
Fine on a cable, poor on WiFi	The router or where it sits	Your side, and not the line at all
The whole street is off	An outage, or power to the network	NBN's

On HFC the boundary between NBN’s network and your home is the NBN box. The cable in the street, the tap and the lead-in are NBN’s, which means a lot of HFC faults are theirs to fix. Getting them fixed is easier when you can show what the fault is doing and when, and that is what an HFC fault visit, tested to the boundary and written up, gives you.

This is what a network-side fault looks like. An HFC service in Penshurst had dropped out on and off for close to ten years, worst in the rain. The cabling inside the house was clean, with no splitters. The trouble was in the street pit: a rusted tap, a split seal over the customer’s port, and water sitting in the pit.

Watch: NBN HFC Keeps Dropping Out When It Rains? This 10-Year Fault Finally Makes Sense

What to check before you ring anyone

• Finger-tighten the connector at the back of the box and at the wall plate. A loose connector is the simplest HFC fault there is.
• Look for an old splitter. If the cable from the wall goes through a small metal block with more than one outlet before it reaches the box, that splitter may be the problem. The box should be on a direct line.
• Restart the box. Off at the power point for a full minute, then on, and give it a few minutes.
• Check for an outage on your provider’s page, using your phone’s mobile data.
• Test on a cable. If a laptop plugged into the router is fast and steady, the HFC line is fine and the WiFi is the problem.
• Note the pattern. Rain, a time of day, after a storm. That is the evidence your provider needs.

Check your speed first Test on a cable at the router in the morning and again in the evening. If the evening result is much lower, the slowdown is in the network, not in your home.

And this is the home side. On an HFC service with constant dropouts, the connector at the box wasn’t screwed in properly and the cable still ran through a rusted splitter left from the pay TV days. Our technician tested the cable, fitted a new compression end, took the splitter out and tightened every connection.

Getting the most out of HFC

• Know what your plan can do. HFC was part of NBN’s September 2025 speed boost, along with fibre to the premises, so the speed tiers on HFC changed. The current tiers are on our NBN speed test page.
• Pick a plan for how you use it. A faster plan will not fix evening congestion, and it will not fix WiFi. If evenings are the problem, start with why your NBN is slow.
• Use the router’s best spot, not the wall plate’s. A cable from the box to a router or mesh unit in the middle of the house does more than any new router sitting next to the old pay TV point.
• Cable what you can. A TV, a console or a work computer on a network cable is steadier than anything on WiFi.
• Keep the box on a protected power point if your area gets storms. Surges are hard on HFC equipment.

To see how HFC compares with the other types, see which NBN connection is best.