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 MIL-HDBK-1012/3
a) The following advantages may be attained through
the use of ceiling distribution systems:
(1)
Low initial cost;
(2)
Installation is easy to perform and requires
minimal time;
(3) Installation can also be done after
construction has been completed;
(4) Low-cost moves, adds, and changes. Outlets
can be relocated short distances using the same cable;
(5)
Flexible pathway; and
(6)
Pathway is dedicated to a specific floor area;
b) The following disadvantages are indigenous to
ceiling distribution systems:
(1)
Can be installed only in false ceilings;
(2) Require expensive plenum rated cable when run
in an HVAC plenum ceiling;
(3)
Are susceptible to EMI if not installed
properly; and
(4) May require utility columns to reach the
center of open areas.
c) If cable trays are not installed, then cable
support devices such as rings or hooks must be suspended from the
wall, ceiling, or ceiling support structure using 10 cm (3/8 in.)
all-thread attached to the structure with anchors or beam clamps.
These devices should be located on 1.3 m to 1.7 m (4 ft. to
5 ft.) centers. Ceiling support wires or rods will not be used
to support cables. Cable runs should be designed using
perpendicular paths with 90-degree turns comprised of two
45-degree turns. A zone distribution system may be used. If the
ceiling air space is being used as the air return path for the
HVAC system, plenum cable must be used. This will noticeably
increase the cost of the installation. A cost/benefit analysis
for comparison with other suitable distribution methods should be
performed. Utility columns or building support columns may be
used to access the workstations. Flush mount wall jacks will be
stubbed up into the ceiling in accordance with NFPA 70. Where
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