Information Technology Reference
In-Depth Information
An alternative method will form a temporary splice, even for Category 5e.
TIA-568-C allows one transition point from round to flat cable in a horizontal cable
run. This means that an allowance has been made for the inevitable untwist and
NEXT that would result from terminating each cable end at the point of transition.
Logically, you should be able to insert a plug and jack coupling to repair a cable cut
or short, but that is not really allowed as it amounts to a splice. However, if a quick
solution will get the network back running, this method can be used temporarily
until new cable can be pulled. You should only use a properly rated plug and jack
for the cable's category of operation.
It may seem easier to use two cable-end plugs and an 8-pin F/F coupler for this,
but that is actually two plug/jack combinations, not one. Also, it is very unlikely
that the 8-pin coupler will meet any standard higher than Category 3. In addition,
many of these couplers also reverse the order of the pins, causing yet a different type
of failure.
Finally, mark the point of the splice on your cable map. If the splice is tempo-
rary, you will want to go back and pull a new cable as soon as you can, as the need
to replace the cable will be inversely proportional to how long you wait. If you want
to have a Category 5e facility, but are using only Category 3 applications now, the
splice may work now, but may fail when you upgrade to higher-speed applications.
Kinks, Bends, and Breaks.
The effect of kinks and bends in cable also varies with
the type of cable. Coax cable is probably the most resistant to this type of damage,
because of the size and durability of the cable. However, severe kinks and very
sharp, sustained bends will affect the transmission loss on the cable and may even
cause an impedance reflection that could cause a failure.
Twisted-pair cable may also be subject to transmission impairment due to
kinks or sharp bends. As unbelievable as it may sound, even tight tie-wraps may dis-
tort the cable enough to cause this problem. The real problem with kinks or bends
in twisted-pair cable is that the defect actually distorts the geometry of the cable.
This can easily be observed on the screen of a time-domain reflectometer (TDR).
Distorting the cable shows up as a reflection hump in the returned signal. Severe
bending can actually cause permanent signal impairment. How serious this impair-
ment is will depend on the category of operation and just how near the operating
margins of the link you are operating.
A major source of kinks in cables is the use of boxed (rather than reeled) cable.
These cable boxes are designed to allow the cable to feed in a spiral fashion, with-
out the need for conventional cable spools and reel holders.
Unfortunately, the cable can sometimes feed more than one loop of cable and
the loops get mixed together trying to get out of the feedhole in the box. Other
