UFC 3-535-01
17 November 2005
Table 12-1. Considerations for Cable and Duct Installation
1. Install cables in the same location and running in the same general direction in the same
trench or duct bank. Whenever possible, route cables in straight duct segments between
manholes and handholes, or between light bases.
When practical, route cables and duct rectilinear (parallel and at right angle) to runways,
taxiways, and other surfaces.
2. Separate low voltage (< 600V) from higher voltage cables (> 600V - 5,000V). Separate all
power cables from control, telephone, and coaxial type cables.
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600V and 5,000V power cables should be placed in separate duct, or separated
minimum 10cm (4") if direct buried in trench.
-
Power cables of more than 5,000V must be separated from all other cables by
minimum 25cm (12").
-
All power cables should be in separate duct bank from all control, telephone, coaxial
type cables, or separated minimum 15cm (6") if either is direct buried.
3. If cables are placed at more than one level, the minimum vertical separation should be
same as the minimum horizontal separation. Do not directly overlap cables, in order to
avoid damage during compaction.
4. Do not direct-bury cables under paved areas, roadways, railroad tracks or ditches.
5. Where rock excavation is encountered, install cable in duct. Remove rock to depth of at
least 8cm (3") below required depth of duct, and use adequate bedding material to
provide uniform support along entire length.
6. Trenches for single-duct lines that are not encased with concrete should not be less than
15cm (6") nor more than 30cm (12") wide, and the trench for 2 or more ducts should be
proportionately wider.
7. For duct banks, use interlocking duct spacers at not more than 1.5M (5') to ensure
uniform spacing between ducts and to hold duct in place when concrete encasing.
Stagger joints in adjacent duct at least 0.6M (2').
8. Provide burial below frost line to prevent damage from frost heave if local experience has
indicated problems.
9. Concrete encased duct is recommended where the area is inhabited by digging rodents or
animals. This is to provide physical protection.
10. Slope duct lines where practical for drainage towards manholes/handholes, or duct ends.
11. Provide ground bushings where rigid conduits enter or leave a manhole.
12. Provide whenever possible at least 25 percent spare duct in a duct bank over and above
the planned installation and any known future expansion.
13. Where conduit is bound in pavement or other structural feature, provide conduit
expansion joints when crossing pavement expansion joints. Consider conduit expansion
joints also where local experience has indicated expansion problems.
[See also typical installation details,UFC 3-535-02]
12-1.8.6
Space for Constant Current Regulators
Constant current regulators require adequate space for maintenance access and high
voltage safety. The following minimum spacing is recommended: 1 meter (3 feet) from
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