--- title: "Earthing for shock protection and methods" subject: "Industrial Power Distribution and Illumination" chapter: 2 key: "semester_6/industrial_power_distribution_and_illumination:earthing-protect-human-methods" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/earthing-protect-human-methods site: BCT Engineering --- # Earthing for shock protection and methods Industrial Power Distribution and Illumination · Chapter 2: Earthing - Asked in: 2073 Magh, 8 marks - Video: [Earthing, Types Of Earthing with Diagrams |BEE|](https://www.youtube.com/watch?v=gtfl-YTDSU4) — Trouble- Free - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/earthing-protect-human-methods - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-2 ## Question Explain with example, how earthing can protect human from electrical shock. Explain different methods of equipment earthing system used in industrial building. ## Short answer When a metallic enclosure becomes live, earthing provides a low-resistance path that keeps touch voltage low and lets a large fault current trip protection, while the parallel human draws negligible current (e.g., 230 V motor). Methods include plate, pipe, rod, strip, earth mat/grid, and chemical earthing, each using buried copper/GI electrodes with charcoal/salt treatment to achieve low resistance. ## Answer #### How earthing protects a person from shock When the insulation of a live conductor fails and it touches the metal body of a machine, the body becomes live. Earthing gives the fault current a path to earth of much lower resistance than a human body, and makes the protective device trip. ```text Phase ──[MCB]──────┐ │ insulation fault ┌────┴────┐ │ metal │ ← body │ body │ └────┬────┘ person ──┐ │ earth wire (≈1 Ω) (≈1000 Ω)│ │ ══════════╧═════════╧════ earth Neutral earthed at transformer ``` **Example:** a 230 V motor body becomes live. - **Without earthing:** if a person (body resistance about 1000 Ω) touches it, current through the person is about 230/1000 = 230 mA, which can cause heart fibrillation and death. The fuse does not blow because the current is small. - **With earthing:** the earth wire (about 1 Ω, with the transformer neutral earth) carries a large fault current. The voltage of the body is held low, the person and the earth wire are in parallel so very little current passes through the person, and the large current blows the fuse or trips the MCB in a fraction of a second. An RCCB (30 mA) gives even faster protection. #### Methods of equipment earthing used in industrial buildings 1. **Plate earthing:** a GI plate (60 cm × 60 cm × 6.3 mm) or copper plate (60 cm × 60 cm × 3.15 mm) is buried vertically at least 3 m deep. It is surrounded by alternate layers of charcoal and salt, and a watering pipe is provided. The earth lead is bolted to the plate. Used for substations and large equipment; costly. 2. **Pipe earthing:** a GI pipe of 38 mm diameter and 2.5 m long with 12 mm holes is placed vertically about 3.75 m deep, surrounded by charcoal and salt, with a funnel for watering. It is the most common and economical method. 3. **Rod earthing:** a copper, copper-bonded steel or GI rod (12.5–25 mm diameter, about 1.2–3 m long) is driven directly into the soil. Used in sandy or soft soil where digging is difficult; cheap and quick. 4. **Strip or wire earthing:** GI or copper strips (e.g. 25 mm × 1.6 mm) or wires are buried horizontally in trenches at least 0.5 m deep. Used in rocky areas where vertical electrodes cannot be driven, and as a counterpoise for lines. 5. **Earth mat / grid:** a mesh of buried conductors connected to several rods, used in substations to control step and touch voltages. 6. **Chemical (maintenance-free) earthing:** an electrode in a backfill compound (bentonite/graphite) that keeps resistance low without regular watering. Inside the building, an **earth continuity conductor** runs with every circuit and connects all equipment bodies, conduits and socket earth pins to an earth bus bar, which is connected to two or more earth electrodes. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A 230 V motor body becomes live and is unearthed. A person of about 1000 ohm touches it. What happens? A. About 230 mA flows through the person and the fuse does not blow B. About 23 mA flows and the fuse blows at once C. No current flows D. About 230 A flows through the person Answer: A. I = 230/1000 = 230 mA, which is dangerous yet too small to blow the fuse, so the body stays live. (Key point: Unearthed shock current) 2. How does an earth wire protect a person touching a faulty body? A. It raises the body voltage to protect the insulation B. It stops the supply from reaching the motor C. It increases the resistance of the person D. It gives a low-resistance path so most current bypasses the person and the large current trips the protective device Answer: D. The low-resistance earth path carries the fault current, the person in parallel gets little, and the large current blows the fuse or trips the MCB. (Key point: How earthing protects) 3. Which description matches pipe earthing? A. GI plate 60 x 60 cm buried 3 m B. GI pipe 38 mm diameter, 2.5 m long with 12 mm holes, about 3.75 m deep C. Strip buried 0.5 m horizontally D. Mesh of conductors in a substation Answer: B. Pipe earthing uses a 38 mm GI pipe, 2.5 m long, with holes, placed about 3.75 m deep, and is the most common economical method. (Key point: Pipe earthing specs) 4. When is strip or wire earthing chosen? A. In soft sandy soil only B. In rocky areas where vertical electrodes cannot be driven C. Only inside transformers D. When maintenance-free earthing is needed Answer: B. Strips or wires are buried horizontally in trenches at least 0.5 m deep where driving vertical electrodes is impossible. 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