ELECTRICAL RESISTANCE OF STEEL POLES USED IN TRANSMISSION LINES

An increasing number of utilities are installing metal transmission and distribution poles due to the many advantages of metal poles over wood poles.  The purpose of this white paper is to present evidence that the embedded portion of a representative steel pole offers significant grounding capability.

In fact, the grounding resistance of the embedded portion of a steel pole can be shown to be lower than standard ground rods under specific conditions.

In this white paper, the Numerical Electromagnetics Code (NEC-4) [1] is used to compute the grounding resistance of a variety of grounding electrodes.  NEC-4 is a method of moments [2] code originally designed for the analysis of antennas and scatterers.  

NEC-4 can be used in the computation of ground resistances since it allows for conducting structures over a finitely conducting ground which may penetrate the ground.  Of particular interest is the grounding resistance of a representative steel pole such as a typical 40 foot class 3 steel distribution pole. Read more…

Steel
electrical resistivity = ( electrical resistance * cross-sectional area ) / longitudinal length
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Resistivity of Steel

RESIST.    COND.                SOURCE
ohm-m      SIEMENS/m       % IACS  CODE     MATERIAL
1.611E-07 6.206E+06         10.70   1  Steel, Cast
5.945E-07 1.682E+06          2.90   1  Steel, High Alloy
6.897E-07 1.450E+06          2.50   1  Steel, 304 Stainless
6.897E-07 1.450E+06          2.50   2  Steel, 304 Stainless
7.184E-07 1.392E+06          2.40   1  Steel, 347 Stainless
7.184E-07 1.392E+06          2.40   2  Zircaloy - 2
7.496E-07 1.334E+06          2.30   1  Steel, 316 Stainless
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