Information Technology Reference
In-Depth Information
both, one on each side of the block. The connectors may be used to attach preassem-
bled 25-pair jumper cables or to attach a modular fan-out (octopus) cable.
The fan-out cables, if used, come in several varieties, with 2-, 3-, or 4-pair
modular legs (so they are often not “octo” cables at all). The 4-pair variety fans out
to cable six legs, each terminated in an 8-pin modular plug. The legs may be ordered
to length, but the wire should be stranded twisted-pair wire and rated to the appro-
priate category in order to conform to LAN wiring guidelines. Because the 66M has
50 contact rows, and a 4-pair leg has eight wires to terminate, and eight divides into
50 rows only six times evenly, there are thus six legs from the fan-out when 4-pair
cable legs are used. The last two rows of the 66M are not needed in most pairings,
so only 48 of the 50 rows are used. Similarly, the 3-pair fan-out has eight legs [48
12]. The mod-
ular plugs of fan-out cables may be wired with any of several wiring patterns,
including T568A and T568B. When ordering these fan-out cables, you should spec-
ify which pattern you want, and ensure that the corresponding outlet jack (at the
other end of the station cable) is wired the same. See Chapters 7 and 10 for more
information.
Horizontal station cables (or backbone cables) are routed down the mounting
backboard underneath the 66 block for termination. They are threaded out through
the openings in the side of the mounting bracket where they are to be terminated.
The outer jacket of the cable is removed to expose the wire pairs. The pairs are
fanned out, sorted by color, and routed to the appropriate contact. Each wire passes
through one of the narrow slots in the face of the block. The wires generally enter
the slot that is just above the target contact row and are wrapped down into the
jaws of the contact for termination. The contact has a hook on one prong to help
position the wire until it is punched down.
The side slots hold the wires in place-order, although they do not in any way
support or strain-relieve the wires. (By the way, the process of fanning out, sorting,
wrapping, and terminating wires on a block is called
stitching
. And one
punches
down
the wire with the impact tool, equipped with an appropriate blade for 66-
block termination.)
The 66 block has a TOP marking to indicate the way it should be positioned.
If it is connectorized, the connector pins will be numbered upside down if the block
is accidentally reversed. If the block is not connectorized, mounting it upside down
just looks amateurish (and you will get comments). You should always punch down
all the wires of a station cable, even if you do not intend to use all of them immedi-
ately. It is impractical to later use the extra pairs of a cable if they are not already
punched down, because there is nowhere to terminate them. If, for some reason, you
must install a cable that has more pairs than you generally use (such as a 4-pair
(2
3)
8], and the 2-pair fan-out has 12 legs [48
(2
2)
