Earth Potential = Soil Resistivity x Current / (2 x PI x Distance) Soil resistivity data from a Soil Resistivity Test Site drawings with the proposed construction Electrical data from the power company Phase-to-ground fault current contributed by each power line circuit Fault clearing time Line voltage Subtransient X/R ratio The make/type/number of overhead ground wires on each tower/pole line and position with respect to the phase conductors Ground wire continuity and bonding configuration back to the tower and substation The average distance from tower-to-tower and tower-to-substation Typical tower/pole ground resistance: measured or design values The site-specific maximum allowable voltage that a person can safely withstand The actual voltages that will be experienced at the site during a fault