In larger houses it's not entirely unheard of to be without a standard master socket.
One house I do quite a lot of work at had a Panasonic PABX with two lines directly into it from a BT 201D connection box
which also had two other lines that terminated beyond in standard non-NTE master sockets.
Well, the PABX has gone now, as have all the non NTE master sockets
One of the main functions of the NTE5 is to disconnect the house wiring from the circuit to allow tests to be made unaffected by non-BT problems.
If the BT drop wire comes in and connects via a junction box like the 201D to the back of the RJ45 patch panel, then there is no house wiring involved and plugging the mod-tap into the appropriate RJ45 socket in the distribution panel is equivalent to using a test socket on an NTE5 - provided, of course, that the mod-tap isn't faulty.
Testing with the router directly connected with a mod-tap (and no ADSL filter) at the RJ45 distribution panel is what you want to do to establish whether there is a line issue or not.
Edited by caffn8me (Wed 05-Feb-14 15:34:23)