MIL-HDBK-1004/2A
SECTION 1:
INTRODUCTION
1.1
Scope. This handbook presents data and considerations that are
necessary for the proper design of overhead and underground distribution
systems, submarine cable systems, and substations having medium-voltage (601
to 35,000 V) or low-voltage (up to 600 V) secondaries.
1.2
Cancellation. This handbook supersedes MIL-HDBK-1004/2, Power
Distribution Systems, of 31 March 1988 and Notice 1 of 15 February 1991.
1.3
Technical Factors.
Ensure that design does not violate these
technical constraints.
1.3.1
Feeders. Do not exceed a 3 percent voltage drop for primary
feeders; however, final sizing of feeders is based normally on their current-
carrying capacities.
1.3.2
Current (Ampere) Levels and Interrupting Duties. Keep current
levels and interrupting duties at reasonable values to avoid the use of heavy
conductors and expensive switchgear.
1.3.3
Equipment Requirements. Equipment must, as a minimum, meet all
requirements of the National Fire Protection Association (NFPA) 70, National
Electrical Code (NEC).
1.3.4
Weather Extremes. Where severe extremes of weather occur such as
heavy snow, high moisture, or fog, design should be modified to take such
destructive elements into account. Design for tropical areas shall be in
accordance with MIL-HDBK-1011/1, Tropical Engineering. Design for
distribution in permafrost or frost-susceptible soils should be based on the
guidance given in the U.S. Army Corp of Engineers, TM 5-852-5, Arctic and
Subarctic Construction, Utilities. Locations where contamination by industry
or salt air can occur may require over-insulation of electric lines. Local
practice should usually be followed. The usual service conditions of many
industry specifications are based on ambient temperatures not to exceed 40
degrees C (104 degrees F) and altitudes not to exceed 3,300 feet (1000 m).
Specific industry standards referenced should be checked and unusual service
conditions noted in the project specifications. Transformer ratings (overload
capacity) may be extended or decreased dependent upon ambient temperatures as
covered in Section 2.
1.3.5
Local Codes. Where state safety rules are predominantly accepted as
a standard in that state, such rules may be used provided they are essentially
as stringent as those of NFPA 70, the American National Standards Institute
(ANSI) C2, National Electrical Safety Code (NESC), and approval of
NAVFACENGCOM Headquarters is obtained. An example of such a code is the State
of California Public Utilities Commission, General Order No. 95, Overhead Line
Construction. This code is also of interest because it has more extensive
coverage on armless construction than does ANSI C2, and it contains useful
data on conductors, clearances, typical problems, and illustrative diagrams on
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