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 MIL-HDBK-1012/3
c) Physical construction and load bearing
characteristics of the building and walls (check with building
architect or structural engineer); and
d)
Bend radius.
Improperly installed vertical backbone cables can
result in slippage of cable pairs within the sheath, stretching
of copper wire, broken fiber, or even severe damage to the
structural integrity of the building or walls. The most common
method of securing a vertical cable is to use straps or clamps
sized to meet the outside diameter measurement of the cable
sheath. A minimum of three clamps or straps per floor is
recommended. When selecting straps or clamps to be applied
directly to a cable sheath, the RCDD should ensure that the clamp
or strap is neither too loose, which can result in the cable
sagging or cuts to the sheath or cable, or too tight, which can
result in crimped cable pairs or broken fibers. Clamps and
straps should be secured to a fire retardant plywood backboard or
anchored to concrete/masonry walls in a manner which does not
interfere with the horizontal distribution blocks or equipment in
the telecommunications closet. When large heavy backbone cables
are installed, use a steel support strand as a messenger cable.
The American National Standards Institute (ANSI) C2, National
Electrical Safety Code, Section 26, specifies that the minimum
stress requirements of the messenger cable will not exceed
60 percent of rated breaking strength under load. In most
instances, engineering of the messenger should not exceed 25
percent of the rated breaking strength under load. The cable
should be tied or lashed to the messenger at intervals of 3 ft.
The messenger can then be secured with ties to beam clamps,
anchors, toggle bolts, or wall brackets. It is recommended that
the RCDD obtain a registered structural engineer's approval prior
to finalizing the installation method. When running fiber optic
backbone cable vertically between floors in innerduct, the
innerduct should be interrupted on alternating floors to secure
the cable.
1.8.4
Campus Backbone Physical Support Structure. This
handbook restricts the discussion of outside plant to the portion
between the building and the serving manhole, pole, or building.
The campus backbone physical support structure provides for
routing, access, and protection of backbone cables between
buildings. Backbone cabling of all media types can be routed
between buildings by one of four methods: direct burial,
underground, tunnel, and aerial. Relative cost comparisons
associated with these methods are based on start-up costs and the
assumption that there are no existing support structures.
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