prevent the reduction in structural resiliency. The total cost over the extended
life of the pole is likely to be $250 or less.
This total cost represents 5 percent to 8
percent of pole replacement costs, ranging $3,000 to $5,000. In addition, the
cost of applying preservative treatment
can be considered for capitalization due
to the significant betterment of an asset
through life extension.
A/B COMPARISON OF STRUCTURAL
RESILIENCY AFFECTING SYSTEM
There have been many instances where
one major storm event impacted neighboring utilities. Structural and system
resilience occurred at the different utilities, but the extent of the system resiliency
and structural impact was different. Data
taken from public reports on how two
neighboring utilities fared following a
hurricane is presented in Figure 1. The
numbers for Utility B were adjusted to
account for having 60 percent more poles.
The comprehensive groundline
the poles with earlier stages of decay that
require maintenance or restoration or both.
In contrast, a comprehensive pole
inspection program uses multiple traditional inspection methods and includes
excavation below groundline for greater
accuracy in assessing a pole’s condition.
Such a program also includes removing
early decay and applying supplemental
preservatives to control the decay process
through the next cycle.
Several cycles of a comprehensive
pole management program will maintain the structural resiliency and significantly extend a pole’s service life. Data
shows that the national average pole life
without pole management is approximately 45 years. The average life occurs
when half of the poles are likely to have
a remaining bending strength that is
below code requirements.
In contrast, the national average life of
poles within an effective pole manage-
ment program is 73 years. This life exten-
sion is accomplished through multiple
inspection and treatment cycles that help
resiliency of the wood poles that support
THE ROLE OF WOOD POLES
The NESC’s design criteria are applied
by utilities as construction criteria for
distribution systems, and in large part
for transmission systems. The NESC
ice and wind loading plus the strength
and load factors for the construction
grade are primary factors in providing
the lines’ original “structural resiliency.”
Once poles are installed, however, subsequent structural resiliency depends on
how well utility companies maintain the
original structural resiliency.
Wood pole manufacturing includes
full-length treatment with a preservative
that helps prevent decay deterioration
for many years. At some point, however,
in-service wood poles may decay in the
section from groundline to 18 inches
below, which is, of course, out of sight.
There usually is not enough oxygen in the
soil to support decay deeper than that.
Decay in the groundline zone directly
reduces structural capacity and resiliency. The NESC allows up to a one-third reduction in the required bending strength before a pole is deemed a
“reject” and must be restored or replaced.
POLE MANAGEMENT PRACTICES:
SUPERFICIAL OR COMPREHENSIVE?
Most utilities inspect some portion of
their poles during an annual program,
but their approaches vary and the results
related to structural resiliency are widely different. Some utilities simply require
sounding a pole with a hammer, above
groundline. This method identifies less
than half of current “reject” poles (finding
only the worst of the worst) and few of
5 days 13 days
Utility A Utility B
Factored for having 60% more poles
FIGURE 1: Neighboring Utility Companies Exposed to the Same Hurricane
Comprehensive wood pole management maintains grid structural resiliency, reduces costs: Utility programs vary but data points to
benefits of taking a closer look