How to Split Lines on a 2 Line Phone System

Written by raul avenir
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How to Split Lines on a 2 Line Phone System
Split a two-line phone system to connect the phones to two different numbers. (wireless telephone image by timur1970 from

A two-line telephone system has two individual lines with four wires connected to phones that can switch from Line 1 to Line 2, or from Line 2 to Line 1. Splitting the line makes each phone independent and eliminates the ability of each phone to switch between lines, thus resulting to two separate single-line phones. In order to split a two-line phone system, you will need to replace the single RJ-14 phone jack with two RJ-11 phone jacks, and connect a single-line phone to each jack.

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Things you need

  • Two-plug telephone jack (Line 1 and Line 2)
  • Slotted screwdriver

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  1. 1

    Go to the Network Interface Box or NID mounted on the wall nearest to where your phone cable runs into your house. Open the NID. Unplug the modular connector from its jack to disconnect power and signals from the telephone company, thus preventing any low-voltage shock.

  2. 2

    Go to the two line telephone system wall jack inside your house or office. Remove or unscrew the faceplate of your wall jack using a slotted screwdriver. A two line phone system has an RJ-14 jack with four wires (red, green, black, yellow) connected to it that must be replaced by two RJ-11 jacks that has two wires each. Pull the jack with attached telephone cable gently out of the telephone outlet box and loosen all the terminal screws at the back of the faceplate using a slotted screwdriver.

  3. 3

    Disconnect all the wires attached to the terminal screws on the jack and straighten out any crooked wire. Get your two-plug phone jack and loosen the terminal screws at the back.

  4. 4

    Wrap the green and red wires clockwise around their matching colour-coded terminal screw on the top jack and tighten the screws to complete Line One. Wrap the black and yellow wires clockwise around their matching colour-coded terminal screw on the bottom jack and tighten the screws to complete Line Two.

  5. 5

    Mount the faceplate on the wall telephone outlet box and fasten it with screws using a screwdriver. Plug back in the modular connector inside the Network Interface Device outside your house. Connect a phone to each jack (Line 1 and Line 2) and place a call to each to try both lines. Unlike in a two line phone system, each phone now acts as a single independent line and can not be used to switch or access the other.

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