Case Study:

In a newly constructed apartment in Noida, Uttar Pradesh, an electrician installs the domestic electric wiring system to supply electricity safely to all rooms. The electricity from the power distribution line enters the house through the main supply cable and first passes through the electricity meter and main switch before being distributed to different circuits inside the house. 

In India, households typically receive alternating current (AC) at about 220-230 V and 50 Hz frequency, which powers appliances such as fans, lights, refrigerators, and televisions. 

The domestic wiring system uses three main wires:

• Live wire (phase wire): carries electric current to appliances
• Neutral wire: completes the circuit by returning current
• Earth wire: provides protection from electric shock by safely carrying leakage current to the ground

For safety, appliances in homes are connected in parallel circuits so that each device receives the same voltage and can operate independently. If one appliance fails, others continue working. 

Domestic circuits usually include two types of wiring circuits:

• 5 A circuit: used for low-power devices like lights and fans
• 15 A circuit: used for high-power appliances like heaters, irons, and refrigerators 

Safety devices are essential in domestic wiring. A fuse or Miniature Circuit Breaker (MCB) automatically disconnects the circuit if excessive current flows due to overloading or short circuiting, preventing overheating and electrical fires.

This example demonstrates how domestic wiring systems combine electrical concepts and safety mechanisms to ensure reliable electricity supply in homes.

Questions

Section A - MCQs

1. In domestic wiring, the wire that carries current from the supply to the appliance is:

A. Neutral wire
B. Earth wire
C. Live wire
D. Ground wire

2. Appliances in homes are connected in parallel circuits mainly because:

A. It reduces voltage for appliances
B. Each appliance receives the same voltage
C. Current becomes zero
D. It increases resistance

3. The main purpose of an earth wire is to:

A. Increase electric current
B. Reduce resistance of appliances
C. Prevent electric shock by carrying leakage current
D. Increase voltage supply

4. A fuse or MCB in domestic wiring protects the circuit from:

A. Low voltage
B. Excessive current
C. Lack of electricity
D. Magnetic effects

Section B - Short Answer Questions

1. Why are electric appliances in homes connected in parallel rather than in series?

2. What is the function of a fuse in a domestic electric circuit?

3. Explain how earthing protects users from electric shock.

Section C - Long Answer Question

1. A household uses several appliances such as lights, fans, and an electric heater.

a) Explain the role of live, neutral, and earth wires in domestic wiring.
b) Describe how a fuse or MCB protects the circuit during overloading.
c) What might happen if many high-power appliances are connected to the same circuit at the same time?

Answer Key

MCQ Answers

1. C - The live wire carries current from the supply.
2. B - Parallel connection ensures equal voltage for each appliance.
3. C - Earth wire safely carries leakage current to the ground.
4. B - Fuse or MCB protects the circuit from excessive current.

Short Answer Solutions

1. Appliances are connected in parallel so that each device receives the same voltage and operates independently. If one appliance stops working, others continue to function.

2. A fuse contains a thin wire with a low melting point. When current exceeds the safe limit, the wire melts and breaks the circuit, protecting appliances.

3. Earthing connects the metal body of appliances to the ground through a low-resistance path. If leakage current occurs, it flows into the earth instead of passing through the human body.

Long Answer Solution

a) Role of wires

• Live wire: supplies electric current
• Neutral wire: completes the circuit
• Earth wire: protects users from electric shock

b) Protection mechanism

• During overloading or short circuit, current increases suddenly.
• The fuse melts or the MCB trips.
• The circuit breaks and stops current flow.

c) Effect of connecting many appliances

• Excessive current may flow in the circuit.
• Wires may overheat.
• Fuse may melt or MCB may trip to prevent damage.