NBN explained
NBN connection box lights: what they mean, and what to do when they change
The lights on your NBN box tell you whether the box has power, whether it can see the NBN network, and whether your modem is plugged in. Find your type of box below, match the light, and you will know whether to restart it, ring your provider or look at your own cabling.
On this page
What the NBN connection box is
The NBN connection box is the device NBN fits inside your home to bring the service in. You might hear it called the NBN box, the NBN modem, the connection device, or by the trade name, the NTD. It belongs to NBN and stays with the property when you move. When the box looks fine and the service still is not, that is where an independent NBN technician comes in.
It is not your modem. Your own modem or router plugs into the NBN box and makes the WiFi. So there are two sets of lights in most homes, and they tell you different things. This page covers the NBN box. For the other one, see why your modem lights are on but there is no internet. If your modem is a Telstra Smart Modem, match its light here.
Which box you have depends on your type of NBN:
- Fibre to the premises (FTTP). A white box on the wall, often with a separate power supply beside it.
- HFC. A small black or white box connected to a round, screw-on cable socket.
- Fibre to the curb (FTTC). A small white box plugged into a phone socket and a power point. This is the one that clicks.
- Fibre to the node and fibre to the building. No NBN box inside. Your modem plugs straight into a phone socket.
Not sure which you have? Which NBN connection you have explains how to tell.
How to know if your NBN box is working: the lights are steady and none of them is red. On a fibre to the curb box all four lights are blue. On an HFC box, Power, Downstream, Upstream and Online are all steady green. On a fibre box, Power and Optical are green and the port your modem is plugged into is lit.
Lights flashing, clicking or changed colour? Try this first
-
Restart the NBN box
Switch it off at the power point, leave it for a full minute, and switch it back on. A fibre box with a battery backup unit beside it keeps running on the battery, so ask your provider how to restart it.
-
Wait
Give it a few minutes before you judge the lights. A fibre to the curb box clicks for a short while as it starts. If it keeps clicking and the connection light never comes on solid, waiting longer will not help.
-
Check the cables
Make sure the cable from the wall and the cable to your modem are both pushed in until they click.
-
Check for an outage
Look at your provider's outage page on your phone's mobile data. If NBN is working in your street, the lights will not settle until they finish.
-
Ring your provider
If the lights have not come good, your provider is the one who lodges a fault with NBN. Tell them which light is doing what, and write down the reference number.
Why is my NBN box clicking?
If your NBN box is clicking, you are on fibre to the curb. On this type of NBN, the box inside your home sends power back down the phone line to NBN’s equipment in the pit in the street. The click is the box switching as it tries to send that power and bring the connection up.
- Clicking and flashing blue. The box is trying to power up NBN’s equipment in the street and make a connection. A short burst of this after a power cut or a restart can be normal.
- Clicking that keeps going, and the connection light never comes on solid. The box is not going to connect on its own, and this is not something to wait out. It is a fault on the line, the lead-in or NBN’s equipment. Anything else still connected to that line inside the house is worth ruling out too.
- Clicking and flashing red. The Connection light is red, which means a problem with the power the box sends to the street. This one is a call to your provider.
Two things at your end are worth checking before you ring. Make sure the box is plugged into the first working phone socket and not through an extension lead, a splitter or an old filter. And if the house has several old phone sockets, know that sockets still connected to the copper line are a common reason a fibre to the curb box keeps dropping and reconnecting. There is more on that in what a bridge tap is, and on why this box powers the street at all in what NBN fibre to the curb is.
Fibre to the curb (FTTC) connection box lights
The fibre to the curb box, the network connection device or NCD, has four lights. When everything is working, all four are blue.
Fibre to the curb: pick what your box is doing
The box that clicks. Its lights are blue, not green
A small white box, wider than it is tall, with four lights in a row along the front. It sends power out to nbn’s equipment in the street, which is why it clicks and why it runs warm.
HealthyAll four blue is a healthy box.
- LAN Blue, flickering Connected, and data is moving.
- DSL Blue Talking to the nbn network.
- Connection Blue The power it sends out to nbn’s equipment in the street is working.
- Power Blue The box is on.
What to do. The LAN light flickering is just your traffic. If the internet is still down, look at the modem.
Not right yetIt is powering the street and cannot reach the network.
- LAN Blue The box and your modem are connected.
- DSL Off No connection to the network.
- Connection Blue The power it sends out to nbn’s equipment in the street is working.
- Power Blue The box is on.
What to do. A short burst of clicking after a restart is normal. Clicking that keeps going with DSL never coming on is not something to wait out: it is the line, the lead-in or nbn’s equipment.
FaultThe power it sends to the street has a fault.
- LAN Off No power.
- DSL Off No connection to the network.
- Connection Red A fault with that power. Your provider has to lodge it.
- Power Blue The box is on.
What to do. Ring your provider. Before you accept "it is your internal wiring", ask for it to be tested: this is the exact light we have proved on a building frame with the customer’s cabling out of the path.
Not right yetThe box is online and your modem is not plugged in properly.
- LAN Off No power.
- DSL Blue Talking to the nbn network.
- Connection Blue The power it sends out to nbn’s equipment in the street is working.
- Power Blue The box is on.
What to do. Push the Ethernet lead in at both ends, then try another lead.
Nothing onNo power at the box.
- LAN Off No power.
- DSL Off No connection to the network.
- Connection Off No power.
- Power Off No power.
What to do. Check the power pack. This box has to stay powered: it is what feeds nbn’s equipment in the street.
Light states read from iiNet, nbn FTTC connection device status lights, 17 October 2026.
Reading the modem’s lights instead? They are a different set and they mean different things: the modem lights guide has the same panel for the box that makes your WiFi.
- Power. Solid blue when the box has power.
- Connection. Solid blue when the box is powering NBN’s equipment outside your home. If it is red, contact your provider.
- DSL. Solid blue when the box is communicating with the NBN network.
- LAN. Solid blue or amber when the box and your modem are connected. It blinks as data moves between them, for example when you are browsing.
| Light | What you see | What it means |
|---|---|---|
| LAN | Off | The box has no power or is not connected to a modem or router. |
| LAN | Blue | Successful connection between the box and the modem or router. Flashing indicates local network activity. |
| LAN | Amber | Successful connection between the box and the modem or router. Flashing indicates local network activity. |
| DSL | Off | The box has no power or is not communicating with the NBN access network. |
| DSL | Blue | The box is successfully communicating with the NBN access network. |
| Connection | Off | The box has no power. |
| Connection | Blue | Successful reverse power to NBN equipment outside the premises. |
| Connection | Red | An issue with reverse power. Call your provider for assistance. |
| Power | Off | The box has no power. |
| Power | Blue | The box has power. |
HFC connection box lights
There are two HFC boxes in the field, the Arris CM8200 and the newer Arris CM3500, and they carry the same four lights down the front: Power, Downstream, Upstream and Online. All four steady green means it is working.
The one nbn has installed since early 2025 adds a 2.5G Ethernet port on the back for the faster plans, and that port has a light of its own. The box before it, the one in most homes, has no 2.5G port. The front lights read the same on both.
HFC: pick what your box is doing
The one nbn has installed since early 2025, with the 2.5G port
A black box with four lights down the front and a fixed white cable that locks onto the wall outlet. The newer one has a 2.5G Ethernet port on the back for the faster plans.
HealthyAll four solid green is a healthy box.
- Power Green Power is normal.
- Downstream Green The box can receive data.
- Upstream Green The box can send data.
- Online Green The connection is working.
- 2.5G port, on the back Green A device is connected with a Cat5e or Cat6 lead.
What to do. If the internet is still down, look at the modem plugged into it.
Not right yetLooking for the network and not finding it.
- Power Green Power is normal.
- Downstream Green, slow flash A firmware update, usually ten minutes or less.
- Upstream Off Still looking for a connection, or no power.
- Online Off No connection to the nbn network.
- 2.5G port, on the back Green A device is connected with a Cat5e or Cat6 lead.
What to do. Give it a few minutes from a restart. If it never settles, this is usually the coax: a loose or corroded fitting, or an old pay TV splitter left in the line.
Working on itAn update is running.
- Power Green Power is normal.
- Downstream Green, slow flash A firmware update, usually ten minutes or less.
- Upstream Green, slow flash A firmware update, usually ten minutes or less.
- Online Green The connection is working.
- 2.5G port, on the back Green A device is connected with a Cat5e or Cat6 lead.
What to do. Leave it alone. Ten minutes or less. Do not pull the power on it.
Not right yetIt can see the network both ways and is not online.
- Power Green Power is normal.
- Downstream Green The box can receive data.
- Upstream Green The box can send data.
- Online Off No connection to the nbn network.
- 2.5G port, on the back Green A device is connected with a Cat5e or Cat6 lead.
What to do. Restart it once. If Online stays off, ring your provider: the box is fine and the service is not.
Not right yetnbn says a flashing Power light is a fault with the box.
- Power Green, slow flash A fault with the box itself. That one is nbn’s own, and most providers do not list it.
- Downstream Off Still looking for a connection, or no power.
- Upstream Off Still looking for a connection, or no power.
- Online Off No connection to the nbn network.
- 2.5G port, on the back Off Nothing plugged into the 2.5G port.
What to do. Ring your provider and tell them the Power light is flashing. The box gets replaced.
Working on itYour lead is holding the speed back.
- Power Green Power is normal.
- Downstream Green The box can receive data.
- Upstream Green The box can send data.
- Online Green The connection is working.
- 2.5G port, on the back Amber Connected with an older Cat5 lead, which may not carry your full plan speed.
What to do. Amber means an older Cat5 lead. Swap it for a Cat5e or Cat6 and the port goes green. Worth checking before you complain about speed.
Light states read from nbn, HFC connection box, with iiNet on the models, 17 October 2026.
One state is worth knowing because almost nobody lists it: nbn’s own documentation says a flashing green Power light means a fault with the box itself. Providers’ pages do not carry that one. If your Power light is flashing, say so when you ring: the box gets replaced.
The 2.5G port light is the other one to look at, because it is a cabling fault you can see without any tools. Green means the lead is Cat5e or Cat6. Amber means an older Cat5 lead, which may not carry your full plan speed. People pay for a faster plan, get less than they paid for, and the reason is a ten-year-old patch lead behind the TV unit.
- The Online, Downstream and Upstream lights all flash briefly when the box is first powered on. That is a self-test.
- If the Upstream and Downstream lights are both flashing and the Online light is off, there is no connection to the NBN network. Call your provider.
- If the Upstream and Downstream lights are both flashing and the Online light is on, a firmware update is in progress. Leave it alone and wait.
The port on the back where your modem plugs in has its own small link lights. Green means a cable connection is detected; if it is off, try another network cable. Yellow means an older type of cable is in use, which may hold back the full speed of the service.
| Light | What you see | What it means |
|---|---|---|
| Power | Off | The box has no power. |
| Power | Green | The box has power. |
| Downstream | Off | The box has no power. |
| Downstream | Green | Successful downstream connection. |
| Downstream | Flashing | Searching for a downstream connection. If the Online light is on, a firmware upgrade is in progress. |
| Upstream | Off | Still searching for a downstream connection, or the box has no power. |
| Upstream | Green | Successful upstream connection. |
| Upstream | Flashing | Downstream connection found; searching for an upstream connection. If the Online light is on, a firmware upgrade is in progress. |
| Online | Off | The box is offline or has no power. |
| Online | Green | The box is online and browsing should be possible. |
| Online | Flashing | Downstream and upstream connection found; retrieving setup information from NBN. |
On HFC, a downstream or upstream light that keeps flashing is often about a connection rather than the box: a loose or corroded fitting on the round cable, or an old splitter left in the line from a pay TV setup. How HFC works explains why the round cable matters.
The original HFC box, before 2025
Installed before early 2025. Four lights, no 2.5G port
A black box with four lights down the front and a fixed white cable that locks onto the wall outlet.
HealthyAll four solid green is a healthy box.
- Power Green The box has power.
- Downstream Green Downstream connection made.
- Upstream Green Upstream connection made.
- Online Green Connected.
What to do. If the internet is still down, look at the modem.
Not right yetNo connection to the network.
- Power Green The box has power.
- Downstream Green, slow flash Looking for a downstream connection. If Online is lit too, it is a firmware update.
- Upstream Green, slow flash Downstream found, now looking for upstream. If Online is lit too, it is a firmware update.
- Online Off No connection to the network.
What to do. Both flashing with Online off is the coax more often than the box: a loose fitting, a corroded connector, or an old pay TV splitter in the line.
Working on itAn update is running.
- Power Green The box has power.
- Downstream Green, slow flash Looking for a downstream connection. If Online is lit too, it is a firmware update.
- Upstream Green, slow flash Downstream found, now looking for upstream. If Online is lit too, it is a firmware update.
- Online Green Connected.
What to do. The same two flashing lights with Online lit means an update. Leave it alone.
Nothing onNo power at the box.
- Power Off No power.
- Downstream Off No power.
- Upstream Off No power, or no downstream connection yet.
- Online Off No connection to the network.
What to do. Check the power pack and the socket it is in.
Light states read from iiNet, nbn HFC connection box status lights, 17 October 2026.
Fibre to the premises (FTTP) connection box lights
There are two fibre boxes in Australian homes and they do not carry the same lights. nbn changed the box in September 2025. If yours went in since then it is smaller, it has four lights across the front, and the UNI-D and UNI-V labels are gone. If it went in before that, the lights sit behind a cover and there are ten of them. Find yours below.
The fibre box nbn installs now, from September 2025
Four lights across the front: Power, Optical, Alarm and Port. There is also a LIGHTS ON/OFF button, which switches the lights off without changing anything else, so a box with no lights at all is not necessarily a dead box. The lights do not come back on by themselves if a fault happens later, which is worth knowing before you panic.
This is the box you get if you are upgrading to fibre now. The FTTP upgrade explained covers what happens on the day, and where the new box goes is worth deciding before NBN arrives.
The new fibre box: pick what yours is doing
The one nbn has installed since September 2025
White, smaller than the box before it, on a wall bracket, with a cover along the bottom that hides the cables. Four lights across the front, and a LIGHTS ON/OFF button that turns them off without changing anything else.
HealthyThis is a healthy box.
- Power Green Power is normal and the box is ready.
- Optical Green Connected to the nbn network and able to receive data.
- Alarm Off Working normally.
- Port Green, fast flash Active service with traffic on the port.
What to do. If the internet is still not working, the box is not your problem. Look at the modem plugged into it.
Not right yetStarting up.
- Power Green, slow flash Starting up.
- Optical Off Not connected to the nbn network.
- Alarm Off Working normally.
- Port Off No service on this port, or the router is not plugged in.
What to do. Give it a few minutes. Power settles to solid green, then Optical comes on.
FaultThe box cannot see the fibre.
- Power Green Power is normal and the box is ready.
- Optical Red Lost its connection to the nbn network.
- Alarm Off Working normally.
- Port Off No service on this port, or the router is not plugged in.
What to do. Check the thin fibre lead is pushed home and not kinked or crushed behind furniture. Do not unplug it to look into the end. If it looks fine, ring your provider: this one is on the network side.
FaultThe box has raised a fault on itself.
- Power Green Power is normal and the box is ready.
- Optical Green Connected to the nbn network and able to receive data.
- Alarm Red A fault. The box is not working normally.
- Port Off No service on this port, or the router is not plugged in.
What to do. Restart it once. If the Alarm light comes back, ring your provider and quote it. nbn replaces the box.
Nothing onNo power, or the lights are switched off.
- Power Off No power to the box.
- Optical Off Not connected to the nbn network.
- Alarm Off Working normally.
- Port Off No service on this port, or the router is not plugged in.
What to do. Check the power supply, then check the LIGHTS ON/OFF button. The lights do not come back on by themselves if a fault happens later.
Not right yetThe box is online and your modem is not talking to it.
- Power Green Power is normal and the box is ready.
- Optical Green Connected to the nbn network and able to receive data.
- Alarm Off Working normally.
- Port Off No service on this port, or the router is not plugged in.
What to do. Push the Ethernet lead in at both ends and try another lead. If the port stays dark, ask your provider which port your service is on.
Light states read from nbn, Fibre to the Premises connection box, 17 October 2026.
| Light | What you see | What it means |
|---|---|---|
| Power | Off | No power to the box. |
| Power | Green, slow flash | Starting up. |
| Power | Green, fast flash | Being upgraded, or receiving updates. |
| Power | Green | Power is normal and the box is ready. |
| Optical | Off | Not connected to the NBN network. |
| Optical | Green | Connected to the NBN network and able to receive data. |
| Optical | Green, slow flash | Data moving. |
| Optical | Red | Lost its connection to the NBN network. |
| Alarm | Off | Working normally. |
| Alarm | Red | A fault. The box is not working normally. |
| Port | Off | No service on this port, or the router is not plugged in. |
| Port | Green | Active service, nothing moving right now. |
| Port | Green, fast flash | Active service with traffic on the port. |
There is a four-port version of the same box, with Port 1 to Port 4 lights instead of the one. Port 1 is grey and Ports 2 to 4 are orange, and each port is kept for one service. On those, providers also document the Optical light coming up blue rather than green on the newer XGS-PON fibre, and cycling red, green and blue while a service is waiting to be activated.
The original fibre box, before September 2025
On the older box the lights sit under the cover. To open it, gently push in between the two clips at the bottom and lift the cover up.
The original fibre box: pick what yours is doing
Installed before September 2025. The lights sit behind the cover
White and taller, with the lights behind a cover. Push in gently between the two clips at the bottom and lift the cover to see them. Four data ports marked UNI-D, two phone ports marked UNI-V.
HealthyThis is a healthy box.
- Power Green The box has power. It can look more orange than green, which is fine.
- Optical Green Connected to the fibre network.
- Alarm Green Working, no issues detected.
- UNI-D 1 to 4 Amber, flickering That device is passing data.
- UNI-V 1 and 2 Off No nbn fibre phone service, or it is not in use.
- Update Off Normal. Nothing to do.
What to do. If the internet is still down, the box is not your problem. Look at the modem plugged into it.
FaultThe box cannot see the fibre.
- Power Green The box has power. It can look more orange than green, which is fine.
- Optical Red No connection to the fibre network.
- Alarm Red A fault detected.
- UNI-D 1 to 4 Off Nothing plugged into that port. Only one port is switched on for your service, usually UNI-D 1.
- UNI-V 1 and 2 Off No nbn fibre phone service, or it is not in use.
- Update Off Normal. Nothing to do.
What to do. Check the thin fibre lead is seated and not kinked. If it is fine, ring your provider. This one is on the network side.
FaultRunning on the backup battery.
- Power Red Running on backup battery from the power supply unit, if one is fitted.
- Optical Green Connected to the fibre network.
- Alarm Green Working, no issues detected.
- UNI-D 1 to 4 Amber A device good for up to 1000 Mbps is plugged in.
- UNI-V 1 and 2 Off No nbn fibre phone service, or it is not in use.
- Update Off Normal. Nothing to do.
What to do. If the power is on in the house, the power supply unit or its battery needs looking at.
Not right yetThe box is online and no data port is lit.
- Power Green The box has power. It can look more orange than green, which is fine.
- Optical Green Connected to the fibre network.
- Alarm Green Working, no issues detected.
- UNI-D 1 to 4 Off Nothing plugged into that port. Only one port is switched on for your service, usually UNI-D 1.
- UNI-V 1 and 2 Off No nbn fibre phone service, or it is not in use.
- Update Off Normal. Nothing to do.
What to do. Your modem may be in a port that was never activated. Only one UNI-D is switched on, usually UNI-D 1. Your provider can tell you which is yours.
Nothing onNo power at the box.
- Power Off No power. Every other light will be off too.
- Optical Off The box is disabled. Your provider has to lodge that with nbn.
- Alarm Off No devices connected.
- UNI-D 1 to 4 Off Nothing plugged into that port. Only one port is switched on for your service, usually UNI-D 1.
- UNI-V 1 and 2 Off No nbn fibre phone service, or it is not in use.
- Update Off Normal. Nothing to do.
What to do. Check the power supply unit and the socket. Every other light stays off while Power is off.
Light states read from iiNet, nbn FTTP connection box status lights, 17 October 2026.
| Light | What you see | What it means |
|---|---|---|
| Power | Off | No power supply. All other lights will be off if the box has no power. |
| Power | Red | The box is running on backup battery power from the power supply unit. If there is no power cut, try troubleshooting. |
| Power | Green | The box has power. The light may look more orange or yellow than green. That is fine. |
| Optical | Off | The box is disabled. Call your provider, as they will need to lodge a ticket with NBN. |
| Optical | Red | No connection to the fibre network. |
| Optical | Green | Connected successfully to the fibre network. This light will flash during data transfer. |
| Alarm | Off | The box is working, but no devices are connected. |
| Alarm | Red | Issue detected. |
| Alarm | Green | The box is working with no issues detected. |
| UNI-D 1, 2, 3, 4 | Off | Nothing is plugged into this port. Only one data port is active for a single NBN service, typically UNI-D 1. If that port does not work and you do not know which was activated, call your provider. |
| UNI-D 1, 2, 3, 4 | Amber | A device capable of up to 1000 Mbps is plugged in. This light will flash during data transfer. |
| UNI-D 1, 2, 3, 4 | Green | A device capable of up to 10/100 Mbps is plugged in. This light will flash during data transfer. |
| UNI-V 1, 2 | Off | There is no NBN fibre phone service, or it is not currently being used. |
| UNI-V 1, 2 | Green | One or more fibre phones are off the hook, typically because they are being used. |
| UNI-V 1, 2 | Flashing | One or more fibre phones have been off the hook for more than an hour. If no one is on a long call, check the handsets are back on the hook or cradle. |
| Update | Off | Normal, no action required. |
| Update | Red | The box has failed to download an update. Call your provider, as they will need to lodge a ticket with NBN. |
| Update | Green | The box is downloading an update with no issues. |
The battery, who supplies one now and how long it lasts are in NBN battery backup.
A red Optical light means the box cannot see the fibre. Inside the home, the one thing to check is the thin fibre lead into the box: it should be pushed home and not kinked, crushed or bent tight behind furniture. Do not unplug it to look into the end. If it looks fine, it is a call to your provider.
When the red light is not your wiring
A flashing red light on a fibre to the curb box is a problem between the box and the street. It is common for the person on the phone to say it must be the wiring inside. Sometimes it is. It can be tested rather than argued about.
On one job in a unit block, the customer’s fibre to the curb service had been dropping out for about a week and then stopped altogether. She had been told the fault was in her internal cabling and that fixing it was up to her. We took the connection box down to the building’s main frame and plugged it straight onto the incoming line, with none of her unit’s cabling in the path at all. The link light kept flashing red. Then we tested her internal cabling on its own, and the readings were stable.
So the box could not connect even with her wiring taken out of the picture, and her wiring tested clean. The fault was on the network side, and she had the evidence to take back to her provider.
That is the test in plain terms: take the home’s cabling out of the path and see whether the light changes. If it does, the fault is inside. If it does not, it is not. When it is not, the evidence goes to your provider, and how an NBN fault gets found and fixed covers what happens next.
Where the box sits matters more than people expect
The lights tell you whether the box is working. Where the box sits decides how well everything after it works. A box in the garage or at the far end of the house puts your modem, and your WiFi, in the wrong place for the rooms you actually use.
If the lights are all correct and the internet is still poor in parts of the house, the box may be fine and its position may be the problem. A box can be moved to where the house needs it, or a cable can be run from it to a better spot for the modem.
Getting a new box? Plan where it goes before the day.
Check your speed first If the lights are right and it still feels slow, test on a cable at the modem, then on WiFi in the room that is slow. The two numbers tell you whether it is the NBN or the WiFi.Frequently asked questions
Why is my NBN box clicking?
The clicking box is the fibre to the curb connection device. It clicks while it tries to send power out to NBN's equipment in the street and set up the connection. A short burst of clicking after a power cut or a restart can be normal. If it keeps clicking and the connection light never comes on solid, it is not going to connect on its own: that is a fault on the line, the lead-in or NBN's equipment, and it is a call to your provider.
What lights should be on my NBN box when it is working?
On a fibre to the curb box, all four lights are blue, and the LAN light may be blue or amber and flickers as you use the internet. On an HFC box, Power, Downstream, Upstream and Online are all steady green. On a fibre to the premises box, Power and Optical are green and the data port your modem is plugged into is lit.
Why is my NBN box flashing blue?
On a fibre to the curb box, a flashing blue Connection or DSL light means the box is still trying to connect to the network. A flashing blue LAN light is normal and only shows data moving between the box and your modem. If the Connection or DSL light keeps flashing and never comes on solid, the box is not going to connect on its own. Ring your provider.
Is the NBN box the same as my modem?
No. The NBN box is NBN's connection device and stays with the property. Your modem, or router, plugs into it and makes the WiFi. On fibre to the node and fibre to the building there is no NBN box inside at all, and the modem plugs straight into a phone socket.
Need this fixed rather than explained?
This is written from the field. When the fault needs a technician on site, this is where to go next.
Book