TM
5-811-1/AFJMAN
32-1080
its supporting elements. The NESC permits con-
200-foot span, since this is a commonly used
ductor sags, such that for ice and wind loadings
ruling span. For other ruling spans, manufacturers
applying, the tension of the conductor must not
will be consulted. A ruling span is an assumed
exceed 60 percent of the conductor's rated break-
" d e s i g n span" that assures average tension
ing strength. Also, the tension at 60 degrees F (15
throughout a line of nonuniform span lengths
degrees C), without external load, will not exceed
between deadends and can be calculated exactly by
35 percent of the initial unloaded tension and 25
the following equation where S is distance be-
percent of the final unloaded tension. In the case
tween spans, from 1 span up to n spans. The large
of conductors having a triangular cross section,
variations in temperatures, wind, and ice condi-
such as cables composed of three wires, the final
tions encountered at various military installations
unloaded tension at 60 degrees F (15 degrees C)
makes it extremely important that conductors be
will not exceed 30 percent of the rated breaking
properly sagged. The copper-equivalent sizes, given
strength of the conductor. Refer to the NESC for
in table 6-2, are based generally on assuming that
specific and detailed requirements regarding the
aluminum conductors two sizes larger than copper
application of aerial distribution lines. Both under
are equivalent in ampacity. To sag conductors
normal and maximum ice and wind conditions,
properly, the conductor manufacturer's published
any conductor will not be loaded beyond limits of
data must be used.
safety. In some areas, it may be common practice
to reduce the maximum loaded tension to 40
percent or less.
(eq 6-1)
(1) Initial sags. Typical initial stringing sags
are given in table 6-2 for various conductor
(2) Final sags and tensions. The final loaded
materials, sizes, a n d loading districts for a
tension data shown in table 6-3 indicates final
Table 6-2. Initial Stringing Sags for 200-Foot Spans.
6-3
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