the earth resistance should be less than 1 ohm. if we using
digital earth resistor, then one common method used as
three terminal type and the distance between these three
terminal should be 20 to 30 meters.
normly earth res.value for an industrial area is 1 to 5
res.for rock sail area and residential area, this value is
8 and 1-3 res respectively.further ithink this depends upon
ur mant. capability. this can be maintened by checking
earthing pit time to time. it also depends the size of
earthing patti and the load capicity set against it.
Earth Resistance test to be conducted on summer conditions to achieve the correct value by using an earth resistance tester (From Megger/ Sanwa/ Fluke). The value should be less than 1 Ohm for electrical earth pits and less than 10 Ohm for Lightning protection System. Procedure for testing should be as per the equipment.