Correct Answer - Option 2 : 2.5 m
The rod and pipe electrodes should NOT be less than 2.5 m in length.
Concept:
Earthing:
Connecting a metallic parts to electric machinery to the earth plate or earth electrode (which is buried in the moisture earth) through a thick conductor wire (which has very low resistance)for safety purpose is known as Earthing or grounding
The primary purpose of earthing is to avoid or minimize the danger of electrocution.
Types of Electrical Earthing:
Plate Earthing:
Copper with dimensions 60 cm x 60 cm x 3.18 mm is used.
Pipe Earthing:
A galvanized steel pipe is usually 40 mm (1.5 in) in diameter and 2.75 m (9 ft) in length is used.
Rod Earthing:
A copper rod of 12.5 mm (1/2 inch) diameter or 16 mm (0.6 in) diameter of galvanized steel or hollow section 25 mm (1 inch) of GI pipe of length is used.
Strip or Wire Earthing:
Strip electrodes of cross-section not less than 25 mm x 1.6 mm (1 in x 0.06 in) is used.
