Tech Help Part 3, Wiring

Jacks and plugs are wired to conform to Uniform Service Ordering Code ("USOC") numbers, originally developed by the Bell System, and endorsed by the FCC. One specific piece of hardware can be wired in different ways, and have different USOC numbers. USOC has become an acronym, pronounced "you-sock," and jack wiring schemes are referred to as "USOC codes."

The 8-position modular jack (above) is commonly and incorrectly referred to as “RJ45”. The 6-position modular jack is commonly referred to as RJ11, which may or may not be correct. Using RJ terms often leads to confusion since the RJ designations refer to very specific USOC wiring configurations. The designation ‘RJ’ means Registered Jack, and should be used only for jacks that are connected directly to phone company circuits.

Each of the basic jack styles can be wired for different RJ configurations. For example, the 6-position jack can be wired as an RJ11C (1-pair), RJ14C (2-pair), or RJ25C (3-pair) configuration. An 8-position jack can be wired for configurations such as RJ61C (4-pair) and RJ48C. The keyed 8-position jack can be wired for RJ45S, RJ46S, and RJ47S. The fourth modular jack style is a modified version of the 6-position jack (modified modular jack or MMJ). It was designed by Digital Equipment Corporation (DEC) along with the modified modular plug (MMP) to eliminate the possibility of connecting DEC data equipment to voice lines and vice versa. (This paragraph is based on info from Siemon.)

In the diagrams to the right, you are looking into the opening of the jack. Internal wiring in the jack may have different colors from the wiring that goes to the jack.

For a phone system with a central control unit ("KSU"), you need a"home-run" configuration (what computer guys call "star topography"), with a direct path from each phone jack to the control unit.

In older construction, particularly homes, "loop-through" wiring is more common, where the circuit passes from one jack to another and another.

Loop-through wiring is OK for simple phones and "KSU-less" phone systems.


The traditional 4-conductor "quad" wire with green, red, black and yellow should not be used in new phone installations.


Use 4-pair (8 conductor) Category 3 or 5 wire.

Panasonic phones don't need four pairs, but it's nice to have extra wire in the walls. The cost of extra wire is insignificant compared to the price of opening up walls to add more wire later. Digital phones can work on one pair of wires, but need a second pair for the eXtra Device Port on the back of the phone.

It's nice to have spare wire for additional devices later on, or to compensate for wire damaged by plumbers or squirrels. If you are running new wire, we recommend 4-, or 6-pair 24 gauge to each phone location. Wire is cheap to buy. Installing more wire later on is not cheap, and can be very messy. We sell wire.

Is it better to STRIP or to CRUSH?

Amateur telephone guys strip insulation off wires; but real phone geeks CRUSH the insulation, and then slickly slide it off.

You, too, can crush like the pros, with our developed-for-the-Bell-System long nose crushing pliers made by the tool wizards at Jonard --  the biggest maker of telecom pliers in the US. It's a big time-saver when you're installing jacks or other hardware with screw terminals, because you don't have to stop to look for the tiny stripping hole; and there's no chance of cutting into the fragile copper. The narrow blades fit into tight spaces, but have much more strength than needle nose tools.

The gentleman in the photograph is Reggie "Crusher" Lisowski, the wrestler who made Milwaukee famous. CLICK for more on Crusher and tag team partner Dick the Bruiser.

The young lady to the left of Mr. Lisowski is Sandra Church from original Broadway production of Gypsy, in 1959. (Photo from PhotoFest.)

The chart below shows the "available" wires in both 568A and 568B wiring plans:

How to steal spare pairs from data wiring

The 8-position, 8-pin modular jacks commonly used for 10Base-T and 100Base-T data networks (and commonly mis-identified as "RJ-45" jacks) have eight wires connected to them.

HOWEVER, at the far end, usually a network hub, switch, or router, only four of the wires (two pairs) are connected.

That means that half of the copper running around inside your walls is probably not carrying any data.

If you need to connect another PC, or a phone, where you already have a data jack, and it would be difficult, time-consuming, or costly to run new wire to that location, it could be very tempting to steal a pair or two of the un-connected wires from the existing jack, and connect them to a new jack.

Here's the bad news: If you do this, there are a couple of guys up high on a mountain in Switzerland, or maybe in a Burger King in Silicon Valley, who will be extremely pissed-off at you for violating the hallowed ethernet standards.

Here's the good news: We won't tell them about what you did, and if no one else rats you out, they won't find out; and even if they did find out, they can't fine you or put you in jail or confiscate your tool kit.

The minor warning: Theoretically, there is some loss of data speed when you steal a pair or two, but daring and resourceful and lazy geeks have been doing this for years, and no one noticed any difference in the speed of sending email, playing games or downloading porn.

The major warning: The spare pair scam works with 10Base-T and 100Base-T wiring, not with 1000Base-T, and maybe not with power-over-ethernet wiring. So, know how the network is being used, and how it is likely to be used in the future, before you begin your surgery.

25-pair cable color codes
for punch-down blocks & connectors

  • Electrical devices -- including phones, light bulbs, bicycle horns, hi-fi speakers and air conditioners -- generally use a pair of wires (two wires working together) to complete an electric circuit from and back to a source of power, signal or data.

  • Multi-pair phone and data wire uses an industry-standard color code to distinguish one pair from the others, and to identify the wires within a pair. Each wire usually has a base color and a contrasting stripe, and the other wire in the pair has the opposite colors.

  • The first pair of wires in a multi-pair cable usually has a white wire with blue stripes, and a blue wire with white stripes. There are codes for 25 different pairs.

  • The first wire in a pair is traditionally identified as "tip" and has positive voltage. The second wire in a pair is called "ring" and is negative. The tip and ring terminology refers to the construction of the plugs used in old-fashioned "Lily Tomlin" switchboards.

  • What normal people describe as "gray" is traditionally identified as "slate" in the phone business, to avoid confusion caused by a "GR" abbreviation which could be either green or gray.

  • What most people describe as "purple," is traditionally called "violet" in the phone business. We don't know why "PU" isn't used for purple. Maybe people think "PU" smells bad.

  • Sometimes, half of a wire pair is solid, not striped. For example, you might find a solid blue wire mated with a white wire that has blue stripes.

  • You may also find wire without stripes, such as solid white mated with solid blue (common in underground cable). This can be a major PITA to deal with as pairs get untwisted, and you're not sure which white wire belongs with which colored wire.

  • Older commonly-used phone wire, known as "quad" or "D station wire" had four wires (green, red, black, yellow) in an outer jacket, but not constructed in pairs. This type of wire is considered obsolete today, and should not be used.

  • When phone cables have more than 25 pairs, each group of 25 pairs is wrapped with distinctive colored nylon thread, in a binder group.

  • Although there are fifty-different-colored wires in a common 25-pair cable, there are actually only ten colors used, five for bases and five for stripes. Beginning phone guys generally carry a chart, but eventually memorize the code.

  • Here's a mnemonic device that may help you remember:
    Base colors: White, Red, Black, Yellow, Violet -- "Women Really Believe You're (a) Virgin."
    Stripes: Blue, Orange, Green, Brown, Slate -- "Big Old Guys Bowl Saturday."

  • Be careful, because three colors (blue, black and brown) begin with "B." Wiring diagrams often use BL for blue, BK for black and BR for brown.