A multi-line phone system has three or more telephone lines. Unlike a typical home telephone that can only accommodate a single line, a multi-line telephone set can accommodate three or more lines that can be accessed at the push of a button. Multi-line phones are most often used in business environments but can also be used in a residential setting. Knowing how to wire a multi-line phone can improve your technical skills and save you some money.
Unplug the modular jack for each phone line connected to the Network Interface Device or NID. The NID is the plastic junction box installed on your property by the local telephone company; it is typically located on an outside wall of your home or office building. The junction box connects the incoming lines from the telephone company to your inside lines and then to your telephone. To locate the junction box, follow the telephone cable that runs from the utility pole to your property.
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Feed a CAT-6 cable through the rubber grommet at the bottom of the NID and pull it up into the junction box. Strip off 2 inches of insulation from the end of the cable using your diagonal pliers. Straighten out the exposed twisted wires and strip 1/2 inch of insulation from each wire, using a wire stripper.
Loosen the pairs of red and green terminal screws inside the NID with a screwdriver. A telephone line needs two wires in order to work, so you will need a red terminal screw and a green terminal screw for each incoming line that you want to hook up.
Hook each wire clockwise around its corresponding terminal post and tighten each screw. For a multi-line phone with three incoming lines, for line one, connect the blue with the white stripe to the red terminal screw and the white wire with the blue stripe to the green screw. For the second line, connect the white wire with the orange stripe to the green screw and the orange wire with white to the red screw. For the third line, connect the white wire with green to the green screw and the green wire with white to the red screw.
Run the CAT-6 cable into your home or office and route it the wall nearest to where you intend to place your multi-line phone. Use cable staples to fasten the telephone line to the baseboard, but avoid placing the cable parallel to a power line.
Route the cable into an outlet box mounted in the wall. Measure off one extra foot of wire and cut the cable square. Strip off two inches of plastic insulation using diagonal pliers. Straighten the exposed twisted wires and strip off 1/2 inch of insulation from each wire using a wire stripper.
Loosen the terminal screws behind the faceplate of an RJ-25 jack. Hook each wire to a terminal post as follows: for line 1, blue wire with white stripes to red terminal screw and white wire with blue stripes to green terminal screw. For line 2, connect the orange wire with white to the yellow terminal screw and the white wire with orange to the black terminal screw. For line 3, connect the green wire with white to the white terminal screw and the white wire with green to the blue terminal screw.
Tighten all terminal screws to secure the connections. Mount the jack to the telephone outlet box using the screws supplied with the jack. Go to the NID outside your home and plug in the modular connectors to complete the connection to your indoor phone jack.
Plug a multi-line telephone set into the new RJ-25 jack. Press line 1, listen for a dial tone, and place a call to test the line. Test the other phone lines in the same manner.