Chapter 12 · Question 9

Describe the domestic electric circuit system used in Indian households. Explain the colour coding of the three wires, the standard potential difference and frequency, and why household appliances are connected in parallel.

Answer Revealed

Direct Answer:

In India, electric power is supplied to homes through overhead poles or underground cables. The supply uses three wires: the live wire (red insulation, positive), the neutral wire (black insulation, negative), and the earth wire (green insulation). The potential difference between the live and neutral wires is

220\ \text{V}

, and the AC frequency is

50\ \text{Hz}

. Wires enter through a main fuse into an electricity meter, then through a main switch to the distribution box containing separate fuses for each circuit. Two separate circuits are typically used: a

15\ \text{A}

circuit for high-power appliances (geysers, air coolers) and a

5\ \text{A}

circuit for low-power appliances (bulbs, fans). Appliances are connected in parallel so that each receives the full

220\ \text{V}

supply, can be independently switched on/off, and a fault in one does not affect the others.

Simple Explanation

The electricity that powers your home comes through three wires. The live wire (red) carries the current, the neutral wire (black) completes the circuit, and between them you get

220\ \text{V}

alternating at

50\ \text{Hz}

. The earth wire (green) is your safety net — it is buried in the ground near your house. Your home has two types of circuits: a heavy-duty

15\ \text{A}

line for power-hungry appliances like geysers, and a lighter

5\ \text{A}

line for bulbs and fans. Everything is connected in parallel, which is why you can turn off your fan without switching off your fridge — each appliance gets its own switch and the full voltage.

Exam-Ready Structure

The domestic electric circuit system is a well-engineered safety-oriented distribution network ensuring reliable and independent operation of household appliances. 1. Power supply: In our homes, we receive AC electric power through a main supply (mains), either through overhead electric poles or by underground cables. 2. Wire identification and ratings: (a) Live wire (positive): red insulation cover. (b) Neutral wire (negative): black insulation cover. (c) Potential difference: In India, the potential difference between the live and neutral wires is

220\ \text{V}

, with a frequency of

50\ \text{Hz}

. (d) Earth wire: green insulation cover, connected to a metal plate buried deep in the earth near the house. 3. Circuit path: Wires pass through a main fuse into an electricity meter, then through the main switch into the house's line wires. From the distribution box, separate circuits are drawn (Fig. 12.15). 4. Separate circuit divisions: (a)

15\ \text{A}

current rating circuit: for appliances with higher power ratings, such as geysers and air coolers. (b)

5\ \text{A}

current rating circuit: for low-power appliances such as bulbs and fans. Each circuit has its own fuse in the distribution box. 5. Parallel connection of appliances: (a) Each appliance is connected in parallel across the live and neutral wires. (b) This ensures each appliance receives an equal potential difference of

220\ \text{V}

. (c) Each appliance has a separate switch to turn the current flow ON or OFF independently. (d) If one appliance develops a fault or is switched off, other appliances continue to function — a series connection would make this impossible. 6. Safety: The main fuse and the individual fuses in each circuit protect against overloading and short-circuiting.

Key Points

Three wires: live (red, positive), neutral (black, negative), earth (green, safety)
Potential difference: $220\ \text{V}$ ; frequency: $50\ \text{Hz}$ (AC supply in India)
Two separate circuits: $15\ \text{A}$ for high-power appliances, $5\ \text{A}$ for low-power appliances
Appliances connected in parallel — each gets full $220\ \text{V}$ , independent switching, fault isolation
Circuit path: mains → main fuse → electricity meter → main switch → distribution box → separate circuits

Describe the domestic electric circuit system used in Indian households. Explain the colour coding of the three wires, the standard potential difference and frequency, and why household appliances are connected in parallel.