Domestic Electric Circuits MCQs Quiz | Class 10

Understanding Domestic Electric Circuits

Domestic electric circuits are fundamental to modern living, powering our homes and appliances. They are designed to distribute electricity safely and efficiently, incorporating various components and safety mechanisms to protect users and property.

Key Components of a Domestic Circuit:

• Main Supply: Electricity typically enters the home from utility poles or underground cables.
• Service Fuse (Company Fuse): A high-capacity fuse installed by the electricity supply company, located before the meter, to protect the main supply line.
• Electricity Meter: Measures the total electrical energy consumed in the household.
• Main Switch: A switch that allows the entire household electrical supply to be turned on or off.
• Distribution Board: Contains Miniature Circuit Breakers (MCBs) or fuses for different sub-circuits (e.g., lighting, power sockets). Each MCB/fuse protects a specific part of the house wiring.
• Sockets: Points where appliances are plugged in. Common types are 5A (for light appliances) and 15A (for heavy appliances like geysers, ACs).
• Wiring: Comprises three main types of wires: Live, Neutral, and Earth.

Safety Devices and Principles:

Safety is paramount in domestic electrical systems. Several devices and practices are employed:

• Fuses and MCBs (Miniature Circuit Breakers): These are crucial safety devices that protect circuits and appliances from overcurrents (due to overloading or short-circuiting). A fuse melts and breaks the circuit when current exceeds a safe limit, while an MCB automatically switches off. Both need to be reset or replaced after tripping/blowing.
• Earth Wire and Earthing: The earth wire provides a low-resistance path to the ground for fault currents. Metal casings of electrical appliances are connected to the earth wire. If a live wire accidentally touches the metal casing, the current flows to the earth, blowing the fuse/tripping the MCB and preventing severe electric shock to anyone touching the appliance.
• Insulation: Wires are covered with insulating materials (like PVC) to prevent accidental contact and short circuits.

Wiring Basics:

• Parallel Connection of Appliances: All domestic appliances are connected in parallel to the main supply. This ensures that each appliance receives the full supply voltage (220V in India) and can be operated independently without affecting others. If one appliance fails, others continue to work.
• Wire Colour Coding (Indian/International Standards):

Wire Type	Old Colour Code (India)	New Colour Code (International)	Function
Live Wire	Red	Brown	Carries current at high potential (typically 220V).
Neutral Wire	Black	Light Blue	Completes the circuit, usually at zero potential.
Earth Wire	Green	Green/Yellow Stripe	Safety wire, provides path for fault current to the earth.

• Voltage and Frequency: In India, the standard AC supply for domestic use is 220-240V with a frequency of 50 Hz.

Common Electrical Faults:

• Overloading: Occurs when too many electrical appliances are connected to a single socket or circuit, drawing excessively large current from the supply. This can lead to overheating of wires and potential fire hazards.
• Short-circuiting: Happens when the live wire and the neutral wire come into direct contact, often due to damage to wire insulation. This drastically reduces the circuit resistance, causing a very large current to flow, which can generate immense heat and sparks, leading to fires.

Quick Revision Points:

• Domestic appliances are connected in parallel for independent operation and uniform voltage.
• Fuses and MCBs protect against overloading and short-circuiting.
• The earth wire prevents electric shocks by safely diverting fault currents.
• Live, neutral, and earth wires have specific functions and colour codes.
• Overloading is due to excessive current draw; short-circuiting is due to direct contact between live and neutral wires.

Extra Practice Questions:

1. Explain why household appliances are connected in parallel and not in series.
2. What is the primary function of a fuse or an MCB in an electric circuit, and how does it achieve this?
3. Describe the role of the earth wire in domestic wiring and how it protects users from electric shock.
4. Distinguish between overloading and short-circuiting in a domestic electric circuit, providing a cause for each.
5. Name two safety precautions one should take while using or working with electrical appliances in a household.