Why Stone/Grable are recommended to use in the Electric Switch yard?

Reason behind the use of Stone/Grable in Switch yard:

     1. In the one hand, Stone/grable increases the Step Potential. Due to substation grounding by mesh earthing, the fault current flow though the low resistance path that is ground. On that time, the step potential created by any men or people is reduced by stone. Now the question is HOW?
The ANSWER is, the foot surface area reduced by grable used in the switch yard. When the touch surface area decreases the resistance increases. 

On the other hand, stone reduces he step potential when operators work on switch yard. 

     2. Stone prevents the gathering of water in side the switch yard in the rainy season due to non uniform surfaces of the stones.

    3. Stone protects the grown of small weeds and plants in the switch yard. There is a question arises, What is basic disadvantage of growing small plants? 
The ANSWER is, grass will form moisture and it may cause the current leakage of substation equipment. 

     4. Transformer are filled with the oil. So oil leakage may occur in the time of changing the oil. Stone provides the protection from fire when oil spillage takes place.

     5. Stone absorbs the heat radiated by sun during the summer season. 

     6. Stone improves the working condition of the switch yard.  

     7. Stone restricts the entry of animals and wild into the switch yard in some extent.