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 MIL-HDBK-1012/3
1.5.1.5
Tray and Ladder Systems. Cable trays and ladders are
rigid structures installed for orderly routing, support, and
containment of telecommunications cables. Various types are
available ranging from open ladders to closed or open top
troughs. As with in-floor ducts, trays may be sized by
allocating 6.25 sq. cm (1 sq. in.) of cross sectional area to
every 10 sq. m (100 sq. ft.) of usable floor space being served.
Tray and ladder systems may be run above or below the ceiling and
under access floors. These wireways should be supported by
brackets, rods or trapeze every 129 mm (5 ft.). A minimum of 310
mm (12 ft.) must be provided and maintained above the wireway.
Coordination with the electrical and HVAC engineers is required
to avoid conflicts in space allocation. Where solid or slotted
ladder/tray bottoms are not mandated, care should be taken to
avoid applying excessive cable weight over CAT 5 or fiber optic
cables. Excessive weight may result in crimped CAT 5 or
fractured fiber.
1.6
Telecommunications Closets. The telecommunications
closet serves as the transition point between the horizontal and
vertical distribution pathways. It is the cross connect point
between the backbone and the horizontal distribution cables
serving the workstations in the area. To function in this
capacity the telecommunications closet must contain: cross
connect fields, patch panels, fiber optic interfaces, and LAN
hardware. Depending on the customer LAN requirements, it may
also house electronic equipment for remote distribution of voice
and video. Where central LAN and PBX switching equipment is
collocated with horizontal distribution cross connects, the
closet should be termed "equipment room" as described in par.
1.8.9. This handbook does not address electrical power
distribution, environmental monitoring systems, various alarms,
design of digital switch systems, LAN hardware, or the logical
network configuration. The RCDD, however, will be responsible
for ensuring that the telecommunications closets and the
equipment room are sized and equipped to accommodate these
systems. The telecommunications closet must be centrally located
in the area being served so that horizontal cable runs are
minimized and no horizontal cable run is greater than 90 m
(295 ft.). If this is done, the average cable run should be
approximately 30 m (100 ft.). There will be a minimum of one
closet per floor. Additional closets will be required if the
floor area exceeds 1000 sq. m (10,000 sq. ft.) or because of the
shape of the area the horizontal distribution distance to the
workstation exceeds 90 m (295 ft.). Multiple closets serving the
same floor shall be linked together by a minimum of one 78 mm
(3 in.) conduit. A 200 pair copper cable and 12 strands of
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