Information Technology Reference
In-Depth Information
run. This means that you must use the T568A wiring pattern at the workstation out-
let if T568A was used at the patch panel termination. Keeping this straight is much
more difficult if you use preassembled octopus (fan-out) cables for your equipment
connection. Be certain which wiring pattern standard is used with the octopus cable
and use the same at the workstation outlet jack. Using different wiring patterns
results in a reversed-pairs indication on a tester. See Part 2 of this topic for more
details on these color codes and wiring patterns.
There are nearly as many ways to connect station wires to modular jacks as
there are modular jack manufacturers. The most confusing jack wiring problems
stem from the fact that the pairs are not connected to the pins of the modular jack
in the same order as they are punched down in the telecommunications room. For
example, in the telecommunications room, the cable is terminated on the 66M or
110 block in the pair order 1, 2, 3, and 4. That means that the blue-white Pair 1
gets punched down first on the first two pins of the cable position, the orange-white
Pair 2 on the next two positions, and so on. At the modular jack, however, Pair 1 is
terminated such that it connects to Pins 4 and 5. The orange-white or the green-
white pair is terminated on Pins 1 and 2, depending on whether you are using the
T568A or T568B wiring pattern. If the terminations on the jack module are num-
bered the same as the pin order, you must be sure to place the wires into the correct
slots before you terminate them. This order will be very different from that on the
punchdown block. Fortunately, many jack modules have color-coded wire slots, so
you can ignore the confusing position numbers.
If you choose to split your station cables into two jacks, with two pairs per
jack, you will have extra fun figuring out what color code to use at each jack. If you
must do this, one approach is to call each pair in a 2-pair set Pair A or Pair B. Plan
which pins on the modular jack should respond to each pair, and draw a connection
diagram, skipping the unused wire positions on the jack. This avoids the obvious
difficulty you would have placing your Pair 1 in the Pair 2/3 position at the jack. Of
course, all of the color codes on the jack will be completely wrong, but you wanted
to do it this way, didn't you?
A far better approach, and one that is allowed by TIA-568-C, is to wire up the
jack with the normal T568A or B pattern and use an adapter cable external to the
outlet jack. Simply make (or have made) an adapter that connects two 2-pair cables,
terminated in two plugs at one end, to a single modular plug, with each wire placed
appropriately. That will split out the station cable to the two applications and avoid
making your jack plate totally nonstandard.
Wrong Category.
Another common failure of high-performance applications
results from the use of the wrong category of cable and/or connectors. Either mis-
