A. 3 m
B. 3.5 m
C. 2.5 m
D. 4 m
Answer: C. 2.5 m
Explanation:
Hollow GI rod electrode is used for pipe earthing.
In pipe earthing method the galvanized steel and perforated pipe of approved length and diameter in place upright in permanently wet soil.
The size of the pipe depends upon the current to be carried and the type of soil.
The size of the pipe uses for earthing is of diameter 40 mm and 2.5 meters in length for ordinary soil or greater length in case of dry and rocky soil.
The depth at which the pipe must be buried depends on the moistures of the ground.
The pipe is placed at 3.75 meters.
The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth's resistance respectively.
Generally, 10 kg of charcoal and 10 kg of salt are used for this purpose.
Another pipe of 19 mm diameter and a minimum length of 1.25 meters are connected at the top of the GI pipe by reducing the socket.