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 MIL-HDBK-1012/3
(1) Even though the in-floor ducts or cellular
system components reduce the amount of construction material
required for the floor and in the case of cellular strengthens
the floor, their cost is high;
(2) Junction boxes are required at each 90-degree
turn and may become saturated over time;
(3) Access hole may not be easily accessible once
furniture has been placed;
(4) New access holes require a core bore through
the floor and into the duct which could damage existing cables;
and
(5) These systems do not lend themselves to
frequent system reconfiguration.
c) In-floor pathways shall conform to the design
criteria of EIA/TIA 569, par. 4.2 which delineates the fill
capacity and concrete cover depth requirements for each type.
The practice of allocating two cables and 10 sq. m (100 sq. ft.)
of workspace to each workstation results in an industry practice
of designing 6.25 sq. cm (1 sq. in.) of cross sectional duct for
each workstation. This applies to both feeder and distribution
ducts (EIA/TIA 568, par. 4.2.1.4.1). Refer to Example Two for
assistance in estimating quantities of in-floor ducts. The
horizontal distance restrictions of EIA/TIA 568 (295 ft.) apply.
BICSI recommends that the distribution duct nearest the wall
parallel to the run be located 18 in. to 24 in. from the wall, to
allow room for furniture along an office wall, and the remaining
ducts spaced at convenient intervals between the building
supports. Preset inserts for access to the cables shall be
located at regular intervals depending on the furniture design
but at least every 17 m (50 ft.). Ducts shall enter the
telecommunications closet either via a floor trench located along
the closet wall or through elbows that terminate beneath the
plywood backboard of the closet. Elbows shall terminate 5 cm
(2 in.) AFF.
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