Abstract :
The results of an extensive study conducted using a computer program designed to determine grounding performance in two-layer soils [1,2,3,5] are described and discussed. A variety of grounding grid configurations and two-layer soil conditions are analysed in detail. The calculated grounding resistances, step and touch potentials are summarized in several charts which could be used conveniently for practical design purposes. The results obtained prove that in general, conventional methods of analysis, such as the IEEE 80 method [4] which uses "Km & Ki" irregularity factors, fail to predict accurately grounding grid performance. Also, it is shown that there are certain grid configurations and/or burial depth, which lead to optimum touch or mesh potentials. Finally, it is shown that certain two-layer conditions will lead to considerably higher touch (or mesh) potentials than the other comparable alternatives.
