Ground Grid Analysis

Accuracy of the algorithm was quantified on the basis of the accuracy of two key ground grid parameters:
(1 ) ground grid resistance to remote earth, and
(2) voltage on the surface of the earth over the ground grid.

The following list of parameter and location constraints was identified in error control. Using these constraints, the relative error in the simplified structures is less than one percent.

1. Horizontal Conductor Constraints

With uniform segmentation the maximum size of a horizontal conductor segment should be smaller than or equal to three times the depth of the conductor. (Maximum horizontal segment size can be relaxed to a size of 6 times the depth of the conductor for 2 percent accuracy.)
The minimum size of a horizontal conductor segment should be greater than or equal to three conductor diameters.
Horizontal conductors should not be located within 10 conductor diameters of a soil boundary layer or earth surface.

2. Ground Rod Constraints

The minimum size for any ground rod segment should be equal to or greater than three ground rod diameters.
No vertical ground rod segment should be greater than one-half the rod length.
The top of the ground rod should be located below the earth surface by a distance equal to at least 10 rod diameters.
1. A top segment with length equal to the burial depth of the top of the rod.
2. A next-to-top segment with length equal to three times the burial depth of the top of the rod.
3. A bottom segment of length equal to the greater of 10 percent of the rod length or three times the burial depth of the top of the rod.
4. A connecting segment between the second and last segments. Additionally, for two-layer earth models, it is always required that rods be segmented at the layer boundary.

3. Error Factor Constraints

The error factors used in the FUNCTION RM and the FUNCTION RXY should be positive and less than 0.01 and 0.001, respectively.