Connecting a BT Extension Socket

aardvaak

Why is it that the incoming line from outside at the master socket only uses 2 wires and extension sockets use 3 wires?

Owain_Moneysaver

The master socket has a component called a capacitor which separates the alternating current ringing signal from the direct current speech signal. Telephone bells are wired through the capacitor.

This was done in the days of electromechanical bells and loop-disconnect (pulse) dialling to stop other phones on the line 'tinkling' when dialling out. With electronic ringers and DTMF dialling, it's mostly irrelevant. Many modern phones won't use the third (bell) wire.

Neil_Jones

You may also have noticed that there are six connectors on the boxes but only ever four are connected. Its numbers 2 and 5 that carry the signal. 3 is the bell wire (not used these days except for legacy phones that literally ring) and number 4 was connected to make it look neat. I dare say more modern installations probably don't have number 4 connected as it doesn't actually do anything but you'll find it in older installations that have been there forever and a day.

DoaM

And all you need is 2 and 5 ... in fact it is best to disconnect any other wires as these otherwise act as aerials and can cause (local) broadband issues.

esuhl

I think this is the wiring diagram, if you're interested:

http://www.davefrydoes.co.uk/wp-content/uploads/2016/04/BT-Master-Socket-NTE5a-Wiring-Diagram-Latest-Version.png

Neil_Jones

As was already said you don't need number 3. The bell wire used to in the days of ADSL cause no end of interference on longer lines and it used to be recommended to disconnect it. For fibre it presumably still can interfere but since the line speeds are faster anyway it's probably not as important as it used to be. And number 4 may be connected (in older installations) but doesn't actually do anything.

You can use CAT5e or CAT6 network cable which you can pick up fairly cheaply in various lengths and it will act as an extension cable - you just need to get an extension plate.

Everything is documented here:
http://www.rob-r.co.uk/other/UKphonecatwiring.htm

aardvaak

Neil_Jones wrote: »

You may also have noticed that there are six connectors on the boxes but only ever four are connected. Its numbers 2 and 5 that carry the signal. 3 is the bell wire (not used these days except for legacy phones that literally ring) and number 4 was connected to make it look neat. I dare say more modern installations probably don't have number 4 connected as it doesn't actually do anything but you'll find it in older installations that have been there forever and a day.

Thank you


So if only using modern phones could I successfully use only 2 & 5?

Neil_Jones

As was already discussed you only need numbers 2 and 5. Number 3 may be needed for legacy telephones (ie a Bakelite or something like that) but otherwise, almost certainly not needed.