---
title: "Short note: Earthing system"
subject: "Basic Electrical and Electronics Engineering"
chapter: 4
key: "semester_1/basic_electrical_and_electronics_engineering:short-note-earthing-system"
source: https://www.bctengineer.com/q/semester_1/basic_electrical_and_electronics_engineering/short-note-earthing-system
site: BCT Engineering
---

# Short note: Earthing system

Basic Electrical and Electronics Engineering · Chapter 4: Electrical Installations

- Asked in: 2081 Baishakh (new course), 3 marks
- Video: [Earthing Systems Explained: TT, TN-S, TN-C, TN-C-S & IT (Complete Guide)](https://www.youtube.com/watch?v=PYCH4yRwbAk) — Gaurav J - TheElectricalGuy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/basic_electrical_and_electronics_engineering/short-note-earthing-system
- Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_and_electronics_engineering/chapter-4

## Question

Write a short note on Earthing System.

## Short answer

Earthing connects non-current-carrying metal parts to earth via a low-resistance electrode (pipe, plate, rod) to protect against shock by enabling protective devices to operate. Resistance should be below 5Ω; common methods use GI pipe with charcoal and salt.

## Answer

**Earthing** (grounding) is the connection of the non-current-carrying metal parts of an electrical installation (or the neutral of the supply) to the general mass of the earth through a low-resistance conductor.

**Purposes:**
- To protect people from electric shock if the insulation fails and the metal body becomes live.
- To give a path for fault current, so that fuses/MCBs/ELCBs operate quickly.
- To keep the voltage of the system stable with respect to earth, and to protect equipment from lightning and surges.

```text
 Appliance body --- earth wire (green/yellow) ---+
                                                  |
                                 Earth electrode (pipe/plate)
                                 buried in soil with salt + charcoal
```

**Methods of earthing:**
1. **Plate earthing:** a copper plate (60 cm x 60 cm x 3 mm) or GI plate (60 cm x 60 cm x 6 mm) buried vertically about 3 m deep in alternate layers of charcoal and salt.
2. **Pipe earthing:** a perforated GI pipe (about 38-50 mm diameter, 2-3 m long) driven vertically into the ground; water is poured in to keep the soil moist. It is the most common type.
3. **Rod earthing:** a copper or GI rod driven into the ground.
4. **Strip/wire earthing:** a GI strip laid in a trench.

The earth resistance should be as low as possible, typically below 5 Ω for a house (about 0.5-1 Ω for power stations and large substations). It is checked with an earth tester, and the electrode is watered in dry seasons.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the main safety purpose of earthing metal frames of appliances?
   A. To increase the appliance's voltage
   B. To save electricity
   C. To give a low-resistance path for fault current so people are protected and protective devices operate quickly
   D. To make the neutral wire unnecessary
   Answer: C. If insulation fails, the earth wire carries fault current away, preventing shock and tripping the fuse or MCB. (Key point: Purpose of earthing)

2. Which description of the earthing methods is correct?
   A. Pipe earthing uses a copper plate buried horizontally
   B. Plate earthing is a GI pipe with holes
   C. Rod earthing uses a strip in a trench
   D. Pipe earthing uses a perforated GI pipe driven vertically, with water poured to keep soil moist
   Answer: D. Pipe earthing is the most common type; plate earthing uses a plate buried 3 m deep with charcoal and salt. (Key point: Plate and pipe earthing)

3. What should the earth resistance be like?
   A. As low as possible, typically below 5 Ω for a house
   B. As high as possible so little current flows
   C. Exactly 100 Ω
   D. It does not matter
   Answer: A. A low resistance lets fault current flow easily; below 5 Ω for houses and about 1 Ω for power stations. (Key point: Earth resistance)

## Related in other subjects

- [Purpose of earthing, earthed vs unearthed system](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aearthing-purpose-earthed-unearthed) — Industrial Power Distribution and Illumination, chapter 2
- [Types of earthing system](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aearthing-system-types) — Industrial Power Distribution and Illumination, chapter 2
- [Improper earthing and system grounding practice](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Aimproper-earthing-system-grounding) — High Voltage Engineering, chapter 2
- [Equipment earthing objective and plate electrode size](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aearthing-objective-plate-electrode) — Industrial Power Distribution and Illumination, chapter 2, asked 3×