1. ANSI/IEEE Std 80, Guide for safety in AC substation grounding, 2000.
2. IEEE Std81, Guide for measuring earth resistivity, ground impedance and earth surface potentials of a ground system, 1983.
3. Natural materials as grounding filler for lightning protection system;Jasni,2010
4. Practical evaluation of ground enhancing compounds for high soil resistivities;Galván,2010
5. Variation of soil resistivity and ground resistance during the year;Gonos,2006