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 MIL-HDBK-1012/3
EXAMPLE FIVE
DETERMINING VERTICAL BACKBONE PATHWAY
SLEEVE AND SLOT REQUIREMENTS
The number of 103 mm (4 ft.) sleeves or conduits and the size of
slots required to support telecommunications related vertical
backbone cables between floors may be determined using the table
below:
Area Served
Number of
Above
4 in. Sleeves
Less than 5,000 sq. m (50,000 sq. ft.)
3
5,000-10,000 sq. m (50,000-100,000 sq. ft.)
4
10,000-30,000 sq. m (100,000-300,000 sq. ft.)
5-8
30,000-50,000 sq. m (300,000-500,000 sq. ft.)
9 - 11
Area Served
Size of Slot
Above
Less than 25,000 sq.m (250,000 sq. ft.)
155 mm x 243 mm
(6 in. x 9 in.)
25,000-50,000 sq. m (250,000-500,000 sq. ft.)
155 mm x 465 mm
(6 in. x 18 in.)
50,000-100,000 sq. m (500,000-1,000,000 sq. ft.) 243 mm x 540 mm
(9 in X 20 in.)
100,000-140,000 sq. m (1,000,000-1,400,000 sq. ft.)
310 mm x 540 mm
(12 in. x 20 in.)
140,000-200,000 sq. m (1,400,000-2,000,000 sq. ft.)
375 mm x 620 mm
(15 in. x 24 in.)
1.8.4.1
Direct Burial. Direct burial cable is cable which is
plowed into the ground or placed directly in a trench, usually
620 mm to 1240 mm (24 in. to 48 in.) below grade, or as specified
by local codes. Selection of direct burial should be based on
the volume of aboveground traffic in the area. The direct burial
method is the least expensive of the four options. If an area is
lightly travelled by pedestrian traffic, then direct buried cable
is recommended as the least cost option. Direct burial of cable
requires that the cable meet the manufacturing specifications of
REA PE-39 or REA PE-89 for copper cable. These cables consist of
a polyethylene sheath and are gel filled to prevent moisture
access or buildup. These cables can be armored to protect them
from rodent and gopher damage. Direct burial of fiber optic
cable is not generally recommended but can be done if the cable
is a tight buffered, loose tube, gel-filled cable with armor.
The pathway for direct buried cable should be marked by two
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