One obstacle to replacing traditional phone service with Voice over IP is that for your existing home phone jacks to work, it's necessary to make a change to your inside telephone wiring. Fortunately, this change is very easy to make. In some cases it's as simple as removing a plug from a jack. Still, a basic understanding of how telephone wiring works is useful before attempting to make such a switch.
A basic wiring primer
Traditional telephone service is provided over a pair of wires. Virtually all telephone wiring installed in the past 50 years or so contains at least two pairs of wires, but that does not mean that all phone wiring is suitable for carrying two phone lines. In today's telephone wiring, each phone line is put on a pair that consists of a solid colored wire (such as solid blue) twisted together with a white wire. Usually this white wire will have a stripe of the same color as the solid wire of the pair (so you would have a blue wire paired with a white wire with a blue stripe), so that you don't get the white wires mixed up. Occasionally you'll see variations on this (for example, the mostly "solid" wire will have a white stripe in it) but you can usually tell what the pairs are, in part because the wires in each pair are twisted together inside the cable.
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In newer homes Cat 5 wire is almost always used for communications wiring - if not it will probably be at least Cat 3, which uses the same color coding ("Cat" is short for "category", by the way). Cat 5 wire generally has four pairs, while Cat 3 may have a different number of pairs, generally anywhere from three to six. |
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The primary pair, or "Line 1", is usually the blue and white (with blue stripe) pair. If there is a "Line 2", it is usually placed on the orange and white (with orange stripe) pair. Line three is on the green pair, and line four on the brown pair (if there is a fifth pair, it will be grey, or to use correct telephone company terminology, "slate"). This color coding scheme for multi-line telephone wiring has been used for years.
The outer jacket of this wiring may be blue, green, grey, beige, white, or occasionally some other color (blue is apparently the most popular outer jacket color for Cat 5 wire these days). The same colors are used for 10/100BaseT computer network cables, although the pairs are utilized differently in that situation. With telephone wiring, particularly if Cat 3 wire was used, the actual number of pairs in a cable may vary, but if standards were followed during the installation, the blue and white (with blue stripe) pair is always the primary phone line.
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In older homes, you may find a whole different scheme, called "quad" wiring, which contains four wires colored red, green, yellow, and black. The primary phone line is normally the red and green wires. Sometimes you will find a second line on the yellow and black wires, but this is not good practice because, in quad cable.
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The wire pairs are not twisted together, which can result in "crosstalk" between the two lines. That is the main reason why "quad" wire is rarely seen in homes newer than a decade or so (in fact, it is a violation of a Federal Communications Commission rule to use any wiring that does not meet at least Cat 3 specifications for new and retrofit telephone wire installations made after July 8, 2000).
One other drawback to "quad" wire is that, because the pairs are not twisted, it is much more susceptible to picking up radio-frequency interference (RFI) from nearby transmitters. If you live near a radio station, or even a busy highway where vehicles travel with high-powered transmitters, you may hear interference from these transmitters in your phones. If this is the case, you should definitely consider replacing any "quad" wire with Cat 5 wire ( not just Cat 3 - Cat 5 has tighter twists and resists RFI much better, and costs only a bit more).
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