Strange telephone wiring in our house

We have a new house with most rooms fitted with the German standard TAE NFN telephone sockets. Normally phone sockets are wired with contacts 1&2 connected. These are connected with 5&6 instead. No normal phone seems wired to 5 & 6.

All sockets have direct 6-pole wiring to the Hausanschlussraum (connections room) in the cellar, but only these two are connected. Before I either redo the wiring or get very legal with the House builder who did the wiring, can anyone tell if there is any reason for this strange connectivity?

Assuming you have identified the connections correctly and assuming it's supposed to be being delivered as functioning, then it's wrong. 5 and 6 forward the signal on TAE-N devices - for example an answering machine can forward a call to the phone:

Thanks. Yes I expected 1 and 2 on your diagram but they had wired up 5 and 6 on every socket in the house (about 5). The only ones done correctly is where we had our own electrician in to do the wiring after having a room split in two. One other funny thing is that they used 6-core cable throughout when normally you need just either 2 for analogue or 4 for ISDN.

Thw worrying thing is that it does imply that the people wiring up the sockets were not aware of German practices or supervised. I guess we will end up with another Mangel for the building company (CKV). They, of course, subcontracted the work but we have to go after the the main company.

Unless you knew the planned configuration of your phone system beforehand, it MIGHT be they did this intentionally. Doing it the way the have permits them to test the cabling, and not to disrupt any services when they are connected. It's a 2 minute job to swap the connections. Using 6-core cable is good practice, as it allows all manner of circuit routing - for example you might want to install a splitter in an upper room to make internet connectivity in a home-office easier or centralise a WLAN router, then route outgoing POTS back down the same line to other locations..

Well I have ended up taking the S0 from the Fritz!box (modem/router) in the cellar taking it through to our old Elmeg mini-Anlage. This drops two buses which serve the two ISDN phones we have and the other four rooms and fax we tied into the POTS lines. The main problem was that all the cabling came to the cellar so that is where we had to put the Fritz!box there so WIFI doesn't work much beyond the ground floor. German construction is fairly solid with reinforced concrete between floors. This isn't much good for the kids whose rooms are on the top floor (2nd floor level) or my wife's office on the 1st floor. What I did was to take an old Linksys WIFI router, stick it on the top floor and link it to the cellar via ethernet over powerline. Possibly excessive, but we had some of the kit already and it needed a minimum of wiring changes.