Telephone jack
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A telephone jack (or phone jack) is a jack located on a wall that is used to connect a telephone or computer to the telephone line. Before phone jacks were invented, the cord from the telephone actually went into the wall and the telephone was not movable unless you had a telephone worker come move the telephone to another location.
The tools and equipment used to install telephone jacks are a pair of needle nose pliers, a wire stripper, a screwdriver (Phillips and flat) a small saw or sharp utility knife, telephone wire, electrical tape, a coat hanger that has been straightened out, and a wall plate.
The wire that connects the telephone jack to the telephone line is hidden behind the wall or under the baseboard. Behind the baseboard is probably the easiest way to run the wire and it is run through the wall by using a hammer and finishing nails. In a lot of cases, the cable is simply stapled to the wall surface.
It only takes two wires to connect a phone, but most house wiring contains four wires. The red and green wires are on the two center terminals of a normal phone jack, and the black and yellow wires are on the two outer terminals. This arrangement allows most normal houses to handle two phone lines very easily.
Many (if not most) line cords that people receive when they purchase a phone (to go between the wall jack and the phone) only have the two center wires. To save money, the outer two are omitted.
When a second phone line is brought into the house, this new line uses the yellow and black wires. If the house has a two-line phone, then the phone is normally ready to accept the second line automatically on the yellow and black wires. Only one line cord is plugged into the phone and it splits the two lines inside the phone.
A fax machine cannot be connected to the second phone line by just plugging it into the wall. A little plug-in converter is needed that takes the outer two terminals (yellow/black) of the phone jack and brings them to the center two terminals (red/green). The converter is plugged into the wall and the fax machine into the converter.
Some wall plates contain two phone jacks. These double phone jacks permit the connection of two phones or a phone/answering machine combination. They may be wired for two telephone lines or they can share a single line.
