2torial #0877:
Learn2 Install a Second Phone Line (continued)

Map the jacks

If you have more than one telephone connected to your first line, chances are your jacks are wired together, forming a circuit that starts--and sometimes ends--at the NID.

In some houses, a single cable runs from the NID to a more centrally located junction box. The junction box is usually the size of a wall jack, but it can be several times larger. From here, individual cables run out to each jack. If you have this configuration, you will need to connect line 2 at the NID and the junction box, then run a new cable from the junction box to a new jack (see Step 6). Study how the connections are made in your junction box, then copy them.

How jacks are wired together. The jack where the line from the NID is first connected is the "initial" jack. The phone cable enters the jack and its wires are connected to terminals there. Then the cable exits the jack and runs to the next jack, and so on. At the last jack in line (the "terminal" jack), the ends of the wires are connected to terminals, and no cable exits the jack. Alternatively, the last jack may be wired back to the NID, forming a loop.

If one of these connections is broken, jacks further down the line go dead. So when you rewire one or more jacks for a new phone line (or install a new jack), you need to maintain the existing connections (which service your first phone line) as well as make new ones.

Diagram your circuits. Follow the phone cable from the NID to the first jack it reaches. Then trace it to each subsequent jack until you come to the last jack, or back to the NID. Draw a diagram of your jacks and the lines between them, including the NID, then add in any new jacks you plan to install. This will help you understand what parts of the wiring circuit need to stay intact for both lines to work.