How to Hook Up a Phone Line at the Junction Box

Written by andrew hazleton
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How to Hook Up a Phone Line at the Junction Box
A modern office can require additional phone jacks. (modern electronic desktop image by Yali Shi from

Adding an additional phone line is a simple project, and since homeowners maintain their own wiring, there is no need to contact the telephone company. There is no practical limit to the number of telephones on a single phone line, although the phone company may provide only enough electrical current to ring a few concurrently. Telephone wiring is usually four-conductor wire, although newer homes may have additional wires to allow for expansion.

Skill level:

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Things you need

  • Screwdriver(s)
  • Utility knife
  • Wire strippers

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  1. 1

    Remove the outlet cover or phone jack from the existing telephone junction box. The phone jack is usually held in place with two screws and there should be sufficient slack in the wiring to allow you to access the inside of the box.

  2. 2

    Feed an end of the new phone cable into the back of the box. There should be space in an existing opening and it is acceptable to run more than one phone wire into the junction box through the same hole.

  3. 3

    Use your utility knife to make a single cut about 5 inches long in the outer insulation of the phone wire. Peel the ends of the insulation back to expose the inner conductors and trim the insulation with your wire cutters.

  4. 4

    Strip 3/4-inch of insulation from each of the conductors on the new wire. Phone wire typically has four conductors, although your wire may have more.

  5. 5

    Examine the back of the existing phone jack. There should be four wires, coloured red, green, black and yellow. If the wires do not match these colours, there should be markings on the phone jack to indicate proper wire connection.

  6. 6

    Loosen the screw holding the red wire. Without disconnecting any existing wiring, wrap the uninsulated portion of the new wire around the screw in a clockwise direction. Tighten the screw. Repeat for the remaining wires.

  7. 7

    Remount the jack into the junction box.

Tips and warnings

  • A telephone only requires two wires. The red and green pair are commonly used for the first line and the black and yellow pair for the second. Always connect all four wires, as it will save confusion if you add a second line.
  • When stripping telephone wire, always check for nicks in the wire or exposed conductors. These can cause shorts or noisy connections.
  • Although telephone wiring works on very low voltage, a ringing phone can provide a mild shock. You may wish to disconnect the phone line at the outdoor box before working on phone wiring.

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