--- title: "Earthing purpose and points to be earthed" subject: "Industrial Power Distribution and Illumination" chapter: 2 key: "semester_6/industrial_power_distribution_and_illumination:earthing-purpose-points-earthed" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/earthing-purpose-points-earthed site: BCT Engineering --- # Earthing purpose and points to be earthed Industrial Power Distribution and Illumination · Chapter 2: Earthing - Asked in: 2078 Chaitra, 2+2+4 marks; 2070 Magh, 8 marks (asked 2 times) - 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-purpose-points-earthed - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-2 ## Question What is earthing? Explain its purpose with an example. Mention the points to be earthed in an industrial plant. ## Short answer Earthing connects system neutral or equipment frames to earth for safety, fault clearing and surge protection. Example: an earthed washing machine body allows a large fault current to trip the MCB, preventing shock. Points to earth include transformer neutral, motor and switchgear frames, metal conduits, cable armour, lightning arresters, portable appliances, structural steel and capacitor frames. ## Answer #### Earthing **Earthing** is the connection of the neutral point of a supply system or the non-current-carrying metal parts of electrical equipment to the general mass of earth through a conductor of very low resistance, so that the earth connection is always at earth (zero) potential. #### Purpose, with example 1. **Safety from shock:** keeps exposed metal parts at earth potential. 2. **Fast fault clearing:** gives a low-resistance path so the fuse/MCB trips. 3. **Stable system voltage:** earthing the transformer neutral fixes the phase-to-earth voltage (230 V) and prevents it rising during faults. 4. **Lightning and surge protection:** surge currents are discharged to earth. 5. **Discharge of static charge** in places with fuel, dust or belts. **Example:** a 230 V washing machine has its live wire touching the metal body because of worn insulation. - If the body is **earthed** (earth resistance about 1 Ω), a large fault current (about 230 A) flows to earth. The MCB/RCCB trips at once, and the body is dead before anyone touches it. - If the body is **not earthed**, the body stays at 230 V. A person touching it completes the circuit to earth through the body and gets a dangerous shock. #### Points to be earthed in an industrial plant 1. Neutral point of each supply transformer and generator (system earthing). 2. Transformer tank, generator and motor frames. 3. Metal enclosures of switchgear, panels, MCCs, distribution boards and bus ducts. 4. Metal conduits, cable trays, trunking and the armour and sheath of cables. 5. Lightning arresters and the lightning protection system (down conductors). 6. Metal bodies of all portable and fixed appliances through the earth pin of sockets. 7. Structural steel, cranes and crane rails, metal pipes and tanks (equipotential bonding). 8. Capacitor bank frames and the secondary of CTs and PTs. 9. Handles of operating mechanisms of switches and isolators. 10. Fences and gates of outdoor substations, and stay wires of overhead lines. 11. Equipment in hazardous areas (fuel storage, paint shops) to discharge static. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is earthing? A. Connecting the phase to the neutral B. Connecting the neutral point or non-current-carrying metal parts to earth through a very low resistance conductor C. Insulating all metal parts from earth D. Connecting phases together Answer: B. Earthing keeps those points at earth potential. (Key point: Definition) 2. What does earthing the transformer neutral do? A. Fixes the phase-to-earth voltage and prevents it rising during faults B. Doubles the line voltage C. Removes the neutral current D. Stops all load current Answer: A. System earthing gives a stable 230 V phase-to-earth. (Key point: System voltage) 3. If the live wire touches an earthed machine body, what happens? A. The body stays at 230 V B. Nothing flows because earth is an insulator C. The person carries the full fault current D. A large fault current flows to earth, the MCB/RCCB trips and the body goes dead Answer: D. A low-resistance path causes a large current that trips protection before anyone touches it. (Key point: Washing machine example) 4. Which of these must be earthed in an industrial plant? A. Only the lamps B. Only the incoming phase wire C. Transformer neutral, motor frames, cable armour, panels and lightning arresters D. Only plastic conduits Answer: C. Neutral points, metal enclosures, armour, arresters, structures and fences are earthed. 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