The resistance of an electrode is inversely proportional to the capacitance. In fact, the formula for resistance of any earth electrode is based on the capacitance between the buried electrode and its hypothetical image above the earth. Conductive cement such as EarthLink from Grounding Systems provides an easy, economical way to design and install extensive electrodes. In many adverse grounding situations, the conductive electrode may be the only economic and practical method of obtaining 5 ohms. Cement can be used to augment almost any kind of electrode, and the results are easy to calculate and predict and are permanent.
Cement is well known to contractors to protect buried metal from corrosion.
Not just any kind will do for grounding, however. Conductive cements have over 200 times lower resistivity than ordinary cement C low enough that standard formulas can be used for calculating the resistance of electrodes made with them, just as if the electrodes were made of metal. Conductive cement effectively enlarges the wire, creating a conductive plate. Figure 4 shows a horizontal-strip configuration, or groundbed, and the formula for calculating its resistance. Use one 50-lb bag every 10 ft.