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However, some manufacturers do offer 66 blocks rated at Category 5e that
should operate at the prescribed level of performance if the proper termination pro-
cedures are used. Chapter 7 describes a technique for minimizing the amount of
untwisted wire when using a 66 block.
Many multipair cables are manufactured with a carefully controlled variation
in twist pitch and pair spiraling in order to meet tough performance parameters
such as near-end crosstalk (NEXT) and structural return loss (SRL). These parame-
ters are maintained, at least in part, by the cable jacket that holds the pairs in their
relative places. Cross-connect wire has no jacket, which means that you may have
more difficulty keeping the pairs in approximately the same geometry, but you
should try to do so if possible. It may be beneficial to use cross-connect wire that
already has the number of pairs spiraled together that you need for the jumper con-
nection, rather than making the connection with two or more individual jumper
pairs. Using jumpers with the proper number of pairs will also make wire tracing
and connection easier.
Remember to remove any unwanted jumpers completely. Nothing is more
frustrating than having to fight through abandoned jumpers to trace down a con-
nection or to make a new cross-connect. The cross-connect field should always be
neat and orderly. The jumpers should be placed in wire management brackets or
other devices and loosely bundled. (Hook and loop straps are good for this.) Never
use tight tie wraps to bind jumpers together. The tie wraps distort the pair geome-
try and can produce the same performance degradation as with regular jacketed
cables.
Punchdown (connecting) blocks are intended to have only one wire connection
per contact. That means you should never punch down a second cross-connect wire
in a slot where another wire is already punched. The integrity of the insulation dis-
placement method used in these contacts depends on the tight positioning of the
contact jaws.
The jaws are opened somewhat during the termination of the first wire, and a
second wire will often not make good electrical or mechanical connection with the
contact. The traditional 66 block is the most prone to this type of wiring error,
because incoming and outgoing wires of a connection are lapped over each other as
they are introduced to the block for termination. The cross-connect wires should be
placed on the second (inner) set of contacts on this type of block. The 110 and sim-
ilar types of connecting blocks are less subject to this type of error, because they
physically separate incoming and outgoing wires on opposite sides of the contact
block.
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