What is a bridge tap?

What a bridge tap is

A bridge tap is any phone socket, joint or length of phone cable that is still connected to your line but is not on the direct path from the street to the socket your internet uses.

To see why homes have them, go back to the plain old telephone service. The lead-in cable came from the street to the first socket in the house. From there, the other sockets were wired in one of two ways:

• Daisy chain. A cable ran from socket one to socket two, from socket two to socket three, and so on.
• Star. Sockets two, three, four and five each ran back to the first socket, or to a junction box in the ceiling or under the floor.

Either way, every socket was live, so you could plug a phone in anywhere. That was the point of it. ADSL coped with it too.

On the NBN, only one socket is in use. Every other socket still connected is now a branch of cable hanging off your internet line and going nowhere. Each of those branches is a bridge tap. If your home has more than one phone socket and nobody has changed the wiring, you almost certainly have one, and an independent NBN technician can find it with a test before anything is replaced.

Watch: Bridge Tap Destroying Your NBN Connection? Here's Why

What a bridge tap does to your internet

The NBN signal on a copper line runs at much higher frequencies than a phone call or ADSL did. When that signal reaches the point where the cable branches, part of it runs up the branch to the unused socket, hits the dead end and bounces back.

Your modem or NBN box then receives the real signal and its echo, slightly out of step. It reads that as noise. The results are:

• Dropouts. The modem or NBN box loses its connection and reconnects, sometimes many times a day.
• Lost speed. The line connects at a lower speed than it should, because part of the signal is being cancelled out.
• A service that will not come up at all, when the branches are long or there are several.

One short branch may make little difference. Several sockets on a long daisy chain can take a large part of the speed, or make the service unusable.

1234

1. 1Street
2. 2Join in the wall
3. 3Modem socket
4. 4Spare bedroom socket

Which types of NBN a bridge tap affects

A bridge tap is a copper phone line problem. It matters on the three types of NBN that finish on the old phone wiring: fibre to the curb, fibre to the node and fibre to the building.

Bridge taps and each type of NBN

Type of NBN	Does the internet use the phone wiring?	Can a bridge tap affect it?
Fibre to the curb (FTTC)	Yes, from the pit in the street to the NBN box	Yes. The most sensitive of the three
Fibre to the node (FTTN)	Yes, from the street cabinet to your modem	Yes
Fibre to the building (FTTB)	Yes, from the basement to your unit	Yes
Fibre to the premises (FTTP)	No	No
HFC	No. It uses the round pay TV cable	No

Not sure which you have? See which NBN connection you have.

In our study of 324 filmed fault jobs, bridge taps were the most common single fault we found, and they concentrate on fibre to the curb and fibre to the building.

• 8.6%of the 324 jobs in the study28 cases, the largest specific named fault
• 21.7%of fibre to the curb casesOf our 60 FTTC cases
• 32%of fibre to the building casesOf our 25 FTTB cases

How to tell if you have a bridge tap

A bridge tap cannot be seen from the socket. These are the signs that point to one:

• More than one phone socket in the home, and no record of the others being disconnected.
• Constant dropouts on fibre to the curb or fibre to the node. On fibre to the curb, the lights on the NBN box drop and come back, and the box may click. See why your NBN keeps dropping out.
• Slower than it should be on a cable, at every time of day.
• Buffering on streaming when nothing else is using the connection.
• Noise on the home phone, if you still have one on the line. That is a phone line fault worth testing in its own right.

None of these proves it. Old leads, a corroded socket and faults in the street cause the same symptoms. What they tell you is that the wiring inside the home is worth testing before anything is replaced.

“Bridge tap detected”: what it means when your provider says so

Providers and NBN can test a copper line remotely, and the test can pick up the pattern a bridge tap leaves. If you have been told “bridge tap detected”, or sent a letter saying your service has a bridge tap issue, that is what happened.

Most of the time the test is right, and there are old sockets still on the line. Because the wiring inside the home is yours and not NBN’s, you will be told to arrange a registered cabler yourself.

But a remote test is an indication, not proof. On one job in Picnic Point, a fibre to the curb customer had put up with dropouts for more than a year and held a letter that said bridge tap. We checked under the house. The lead-in ran directly from the one socket to the conduit in the street, with nothing branching off it anywhere. We fitted a new socket and a new lead to rule those out, and the box still would not connect. There was no bridge tap. The fault was on the network side, and that finding went back to the provider so the equipment in the street could be looked at.

So if you are told there is a bridge tap, have it checked on site. If it is there, removing it fixes the service. If it is not, you have evidence the fault is somewhere else.

How a bridge tap is found and removed

The aim is one direct path: the lead-in from the street to the one socket you use, with nothing else connected to it.

1. Find where the line comes in, and which cable is the lead-in.
2. Trace the internal cabling with a tone generator and probe, to learn which cable goes to which socket and whether the house is a daisy chain or a star.
3. Measure the line with everything connected.
4. Disconnect every socket and cable that is not on the direct path. In a star, the spare cables come off at the junction. In a daisy chain, the chain is cut after the socket in use, or the lead-in is joined straight to the cable for the socket you want.
5. Measure again. The difference between the two readings is what the bridge tap was costing you.

Watch: Bridge Tap Removal NBN FTTC. The Work That Makes Internet Faster

If the socket in use is an old one, it is replaced at the same time, so no adaptor is needed. If you want the modem somewhere better, this is the moment to move the socket. Done as a fault repair, the old sockets are taken off the line and the line is measured before and after, so you can see what changed.

Watch: Constant Dropouts on NBN FTTC Service | 5 NBN Techs over 12 months and I Fixed The Job In 15 Min

Who has to fix it

The owner of the home or the building. The phone wiring past the point where the lead-in arrives belongs to the property, not to NBN, so neither NBN nor your provider will remove a bridge tap for you. If you rent, it is the landlord’s cabling, and the landlord or agent needs to approve the work.

In a unit block the line runs through the building’s own wiring first, from the basement or communications room to your unit, and the extra cabling can sit in that part too. That side is the building’s: see faults on fibre to the building and MDF jumpering, the work done at the building’s frame.

Fixed phone and data cabling may only be worked on by a registered cabler. That is the law, and it exists because the cabling connects to a public network.

Keeping bridge taps out of your line

• When the NBN is connected, ask the installer which socket is in use and whether the others were disconnected. It depends who turns up: some installers take the old sockets off the line, and some connect the service and leave the wiring as they found it.
• When you renovate, have old phone cabling taken out or taken off the line, not left in the wall still connected.
• When you add a socket, have it run as its own cable, not joined onto the existing line.
• Keep a note of which socket is the first one. It saves time on every future fault.

Check your speed first Test on a cable at the modem and write the number down. If a bridge tap is removed later, the same test shows what it was costing you.