Answer / p.r.gowri sankar

Earthing Resistance between the phase to earth is must be
below the value is 0.5ohms.

Answer / engr. rohail joses

Normally the Earthing Resistance value while designing Earthing Systems for Power Plants is kept below 1 Ohm, this value ensures Step and Touch Voltages not acceding their safety limits.Also the GPR (Ground Potential Rise) during Lightning Discharge, Line to Line and Line to ground Faults for less than 1 Ohm Earthing Resistance is also confined within its safe limits and Earthing System is with less than 1 Ohm Earth Resistance becomes fully capable to dissipate/ handle this Destructive phenomenon. This is as per IEEE Standard [IEEE Std 80-2000]. However for small substations and Industries Earthing Resistance value of less than 5 Ohm is also acceptable. 

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