MAXIMUM ACCEPTED EARTH RESISTANCE

A paper by US AID India has addressed this issue and indicated the generally accepted resistance value for different applications which may be based on prevailing established practices. Reference of various other standards, documents and books has also been reproduced below:-

US AID | INDIA Earthing Practices by MVS Brinch

a) Power stations (generating station) 0.5 ohms
b) EHT Sub-station 1.0 ohms
c) 33 KV Stations 2.0 ohms
d) D/t Structure 5.0 ohms
e) Tower Foot resistance 10.0 ohms
Modernization of power distributions, Page 92 Same as above.
IEEE standard 142-2007 Chapter 4, page 164
Resistance generally found suitable for industrial plant

Sub-station and buildings and large installations

1 ohm to 5 ohms
IS 2309: 1989, Cl 12.3.1 Page 32 and BS 7430:1998
Cl 9.4.3 Lightning arrestors ground resistance for

Protection of buildings and allied structures

10 ohms

Guide for control of Undesirable Static Electricity
Lightning arrestors ground resistance for Protection

of buildings and allied structures

10 ohms

IS 2689:1989, Table 4 page 28 (Reaffirmed March 2010)
Lightning arrestors ground resistance for Protection

of buildings and allied structures

10 ohms