The horizontal conductor tension is equal at both supports. The vertical component of conductor
tension is greater at the upper support and the resultant tension,Tu, is also greater.
14.1.5 Ice and Wind Conductor Loads
When a conductor is covered with ice and=or is exposed to wind, the effective conductor weight per unit
length increases. During occasions of heavy ice and=or wind load, the conductor catenary tension
increases dramatically along with the loads on angle and deadend structures. Both the conductor and its
supports can fail unless these high-tension conditions are considered in the line design.
The National Electric Safety Code (NESC) suggests certain combinations of ice and wind correspond-
ing to heavy, medium, and light loading regions of the United States. Figure 14.3 is a map of the U.S.
indicating those areas (NESC, 1993). The combinations of ice and wind corresponding to loading region
are listed in Table 14.1.
The NESC also suggests that increased conductor loads due to high wind loads without ice be
considered. Figure 14.4 shows the suggested wind pressure as a function of geographical area for the
United States (ASCE Std 7–88).
Certain utilities in very heavy ice areas use glaze ice thicknesses of as much as two inches to calculate
iced conductor weight. Similarly, utilities in regions where hurricane winds occur may use wind loads as
high as 34 lb=ft^2.
As the NESC indicates, the degree of ice and wind loads varies with the region. Some areas may have
heavy icing, whereas some areas may have extremely high winds. The loads must be accounted for in the
line design process so they do not have a detrimental effect on the line. Some of the effects of both the
individual and combined components of ice and wind loads are discussed in the following.
14.1.5.1 Ice Loading
The formation of ice on overhead conductors may take several physical forms (glaze ice, rime ice, or wet
snow). The impact of lower density ice formation is usually considered in the design of line sections at
high altitudes.
The formation of ice on overhead conductors has the following influence on line design:
.Ice loads determine the maximum vertical conductor loads that structures and foundations must
withstand.
.In combination with simultaneous wind loads, ice loads also determine the maximum transverse
loads on structures.
MEDIUMMEDIUMLIGHTLIGHTLIGHTHEAVYHEAVYFIGURE 14.3 Ice and wind load areas of the U.S.