The minimum size of a copper strip to be used as an earth electrode must be:

Strip earthing:

• This type of earthing is used at places that have rocky earth bed.
• In this system of earthing, the strip electrode of the cross-sectional area not less than 25 mm × 1.6 mm if copper and 25 mm × 4 mm if GI or steel.
• It buried in horizontal trenches of a minimum depth of 0.5 m.
   

Rod earthing:

• This system of earthing is suitable for areas that are sandy in character.
• This system of earthing is very cheap as no excavation work is involved.
   

Plate earthing: It is used for larger stations and transmission lines, where the fault current, likely to be high.

Pipe earthing:

• It is used for ordinary soil or dry and rocky soil.
• The size of the pipe depends upon the current to be carried and the type of soil.
• Usually, the pipe used for this purpose is of diameter 38 mm and 2.5 meters in length for ordinary soil or of greater length in case of dry and rocky soil.