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 MIL-HDBK-1012/3
_________________________________________________________________
EXAMPLE SIX
DETERMINING ENTRANCE DUCT REQUIREMENTS
Entrance ducts to support buried or underground cables entering a
building should never be less than 103 mm (4 in.) in diameter.
Having determined the size of the copper entrance cable or
cables, determine the outside diameters of the cables by
consulting a manufacturer or authorized dealer. Duct fill ratios
should be in accordance with NFPA 70 as restated in par.
1.5.1.3.c). Use the table below to determine number of entrance
ducts required for the size of copper cables being installed. An
additional duct for fiber optic cables and one spare duct for
future telecommunications use should be added to the number of
entrance ducts required for copper cable to determine minimum
number of telecommunications ducts required. Provide
telecommunications duct requirements to the electrical estimator.
Number of
Number of 103 mm (4 in.)
Ducts for:
Copper Pairs
Copper
Fiber
Spare
Less
than 1000
1
1
1
1000
- 2000
2
1
1
2000
- 3000
3
1
1
3000
- 5000
4
1
1
5000
- 7000
5
1
1
7000
- 9000
6
1
1
1.9.1
Equipment Room Location
a) Selection of the equipment room location is
critical to the successful implementation of a functional
telecommunications distribution design. The equipment room
should be located as close as possible to the cable service
entrance point and the vertical distribution pathways. Cables
entering the building via the service entrance are rated for
outside use and are not low-smoke rated cables. As such they are
limited by NFPA 70 to a length of 50 ft. within the building
unless run in rigid conduit. The cable sheath is to be grounded
as soon as possible upon entering the building to reduce the
spread of lightning-induced currents within the building. Copper
cables are to be terminated in the entrance facility on a
composite gas and heat coil protector.
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