Is my house 3 wire or 2 wire?

You have a three wire system, however it also sounds like you have more than one master or a 2wire socket (ie ones with capacitor).

Are you certain which socket is the first in line to the incoming circuit ,it is useful that you know that. If I were you I would replace all sockets with 2wire sockets. These have a "2" on the front. Three wire sockets have either an "M" or "S". There is unlikely to be a junction box other than maybe a join on the outside of the house.

In old three wire systems they were wired like this:

                             M                              S                                                   S
-----------------------2-------------------------------------------2------------------------------------------2
                            _|_
                            _ _
                             |
                             3------------------------------------------3------------------------------------------3

------------------------5------------------------------------------5------------------------------------------5

The master jack had a capcitor from pin2 to pin 3, the speach and DC circuits were via pins 2/5, but the ring current was pulled through the capacitor and pin 3 and returned on pin 5. The purpose of the 3rd ring current wire was to limit ring current, ie all ringers had to pull the current through the one capacitor in the Master jack.

Modern 2 wire systems just have the two wires, each jack has a capacitor in it to support phones that pick up the ring current on the 3rd wire, but most modern phones pick up the ring via the two main wires. 2Wire sockets have two IDC terminals in them, all the pins on each IDC terminal set are wired together so to make it easier to wire multiple feeds through the back of a socket.

As you can see if you know what you are doing it is possible to use 3wire and 2wire sockets in a 2wire wiring.

As for the wired alarm, normally the phone circuit goes directly from the outside interface to the alarm panel, the alarm panel will have a phone line in and phone line out. The line out then goes off to the rest of the house wiring, thus if someone is on the line when the alarm goes off, or the wires ripped out of the socket the alarm panel can still access the phone network and isolate the rest of the house wiring.

The best and correct method to work with an alarm in an existing house that is not star wired, is to place a wired in filter just before the line goes into the alarm. Thus the alarm appears as part of the low band phone circuits. The line out of the alarm is then a filtered feed that should go off to all phone circuits in the house. The direct line before the filter should be connected to the 2nd pair in the phone circuit and go to the first wall socket where the adsl modem is sited. Obviously if that is not the socket you wish to site the adsl modem at then you will need to use suitable terminals to connect the 2nd circuit on to the next jack. You will need to place a 2nd socket at the adsl modem site to connect it to the 2nd unfiltered feed. Ideally once you have got to the jack where you want the adsl modem then dont continue the 2nd circuit as this creates an unwanted stub. Obvoiusly the 1st circuit in the cable will carry the filterd phone circuit to all the sockets in the house.

The above description is for the typical NZ house that was wired with all the phone circuits just running from socket to socket rather than in a star or central location.

Cyril

jai10

cyril7