Q22Basic Electrical Engineering

What is Earthing? Earthing (or Grounding) is the rigorous process of connecting all non-current-carrying metallic parts of electrical machinery (like motor casings or refrigerator bodies) to the general mass of the Earth through a very low resistance wire. If an insulation failure occurs and a live wire touches the casing, the massive fault current safely bypasses the human operator and rushes directly into the earth. This blows the fuse or trips the circuit breaker instantly, isolating the dangerous equipment.

Different Types of Earthing:

• 1. Pipe Earthing: This is the most common and economical method. A heavily galvanized iron (GI) pipe, usually $38\text{mm}$ in diameter and $2$ meters long, is buried vertically deep into a pit in the ground. The pipe has tapered holes drilled along its length. The pit around the pipe is filled with alternating, thick layers of charcoal and salt to permanently maintain high soil moisture and excellent conductivity. A funnel is provided at the top to occasionally pour water in dry seasons.
• 2. Plate Earthing: Used for heavier electrical installations (substations). A large, thick metal plate made of either pure Copper (minimum $60\text{cm}\times 60\text{cm}\times 3\text{mm}$) or Galvanized Iron is buried vertically in an earth pit at a depth of at least $3$ meters. Similar to pipe earthing, it is heavily surrounded by alternating layers of charcoal and salt to increase the effective area of earth contact.
• 3. Strip or Wire Earthing: Used in rocky terrains where deep pit digging is impossible. Long strips of GI or Copper are buried horizontally in shallow trenches.