A Bridge Tap is a length of phone cable, normally unterminated or badly terminated that is connected to your line - could be due to maintenance, previous routing, bad installation or configuration.. It will alter the line characteristics - the impedance of the line will change, there can be reflections of the signal both of which adversely affect the quality of the ADSL/VDSL signal. The length of a bridge tap will determine frequencies and tones it will affect.

edit to add:

In some countries (not-UK) the Telco will run one or more high capacity cables, maybe 50 pair from pole to pole along a road. When service is required they will just tap into the cable and connect the customer to an unused pair. However, the pair is still there and continues on to the end of the road or cable meaning that the customer has a length of unterminated cable on the line.

Edited by MHC (Fri 26-Sep-14 12:38:52)

In reply to a post by b4dger:

Surely if the engineer fits a new faceplate filter to the NTE5 then the home wiring should all be fine?

Sometimes an old extension will have been taken off the incoming pair earlier than the joint box in the hall or living room ... then later disconnected at the extension, but not on the incoming cable. Over time, it gets forgotten.

Perhaps it remained forgotten when old GPO joint boxes were converted into modern master sockets.

An extra bit of wire dangling on the side isn't detrimental to a voice call, and may not even have caused problems on ADSL. But it does on VDSL2.

MHC has given a technical description. This post is about the result.

The (most) common form of bridge tap in UK home wiring is star wiring of extensions.

That arises in older installations where star wiring didn't matter. The line comes in to the premises to a junction box, and some or all extensions are wired from that, including the one that has the master socket on the end. Extensions do not need to be wired from the master for pure phone functions.

In the past the replacement of an old style master by an NTE5 would not normally have resulted in an alteration to that setup. An engineer installation of FTTC should include removal in one way or another of such bridge taps.

A self-install is highly unlikely to include that.

In reply to a post by WWWombat:

An extra bit of wire dangling on the side isn't detrimental to a voice call, and may not even have caused problems on ADSL. But it does on VDSL2.

Normally the length is fairly short, and they tend to affect the higher frequencies which is why VDSL is affected and not ADSL (as much). I have seen Dial-Up affected by very, very long BTs.

With ADSL2+ being up to 2.2MHz, the BT would need to be greater than 35metres in length to have an effect, whereas with VDSL's 17 MHz BTs down to 4m long can have an effect. A long BT will not just affect a single frequency either, there can be a pirmary reflection at 1/4 wave, then further ones at 3/4, 5/4, 7/4 ...

Thanks for replies.
Just checking it was as I thought.

i.e. A correctly installed NTE5 with faceplate filter avoids the 'bridge tap' in a home's wiring you mentioned.

That isn't what I said.

Also, we have had several reports of bridge taps still existing following a Kelly's or Quinn's FTTC installation. Not following an Openreach one.

Edited by RobertoS (Fri 26-Sep-14 16:41:31)

Huh?

I've read the replies (re Bridge taps and home wiring) and understood that if the Master Socket (NTE5) is 'correctly' installed (i.e. direct to incoming phone line with no hidden extensions etc. etc) along with an Openreach supplied faceplate filter then 'bridge taps' isn't an issue with home wiring.

Have I got it wrong?

Just re-read my post, as to how they can arise.

The VDSL2 faceplate filter is irrelevant to the bridge tap question.

Edit - typo.

Edited by RobertoS (Fri 26-Sep-14 17:02:10)

The problem tends to arise when the installer (which could, of course, be a builder or householder) *thinks* he has fitted the NTE5 to the end of the line, but it turns out there is an earlier junction.

The installer will therefore swear blind that the master has been installed correctly, but in reality this is not true.

The trick, of course, is to identify the cases where a master exists and looks to have been installed correctly, but a can of worms lurks somewhere behind the scenes.

Sorry - I'm still not clear then...

I've read the replies (re Bridge taps and home wiring) and understood that if the Master Socket (NTE5) is 'correctly' installed (i.e. direct to incoming phone line with no hidden extensions etc. etc) along with an Openreach supplied faceplate filter then 'bridge taps' isn't an issue with home wiring.

i.e. DSL and voice correctly separated at the faceplate.

Am I wrong in thinking the above?