ScienceCBSE Class 10 · Magnetic Effects of Electric Current

Domestic Electric Circuits

Updated 14 October 2026 · Fact-checked

Homes receive AC mains at 220 V and 50 Hz through a live wire (red) and a neutral wire (black), with a green earth wire for safety. Appliances are wired in parallel so each gets 220 V and has its own switch. A fuse protects against overloading and short circuits, and earthing protects users from shocks from metal-bodied appliances.

Understand Domestic Electric Circuits

The supply. Electric power reaches homes from the mains, through overhead poles or underground cables.

Live wire (usually red insulation), also called positive.
Neutral wire (usually black insulation), also called negative.
In India the potential difference between them is 220 V.
At the meter board, these wires pass into the electricity meter through a main fuse, then through the main switch to the house wiring.

Two kinds of circuit. Houses often have two separate circuits: one of 15 A current rating for appliances with higher power, such as geysers and air coolers, and one of 5 A for bulbs, fans and similar loads.

Earth wire. The earth wire has green insulation and is connected to a metal plate buried deep in the earth near the house. The metallic bodies of appliances such as electric irons, toasters, table fans and refrigerators are connected to it. It provides a low-resistance conducting path, so if current leaks to the metal body, the body stays at the earth's potential and the user does not get a severe electric shock.

Parallel connection. In each circuit, appliances are connected across the live and neutral wires, in parallel. So:

each appliance gets the same potential difference (220 V);
each has its own switch and can be turned on or off independently;
the total current is the sum of the currents drawn by all appliances, so adding appliances increases the current in the main wires.

Fuse. An electric fuse is a key safety component, connected in series. If the current becomes unduly high, Joule heating melts the fuse wire, breaking the circuit and protecting the wiring and appliances.

Short-circuiting and overloading.

Short-circuiting: the live and neutral wires come into direct contact, for example when insulation is damaged or an appliance is faulty. The current increases abruptly.
Overloading: too much current flows because of an accidental rise in supply voltage, or because too many appliances are connected to a single socket.

In both cases the fuse melts and stops the excessive current. Precautions: do not connect too many appliances to one socket, use fuses of correct rating, and keep insulation in good condition.

AC and DC. A cell gives direct current (DC), which flows in one direction only. The mains supply is alternating current (AC), which reverses direction periodically. In India the frequency is 50 Hz, so the current changes direction every $\frac{1}{100}$ s (twice in each cycle). An important advantage of AC is that it can be transmitted over long distances without much loss of energy.

Checking a circuit with numbers. The current drawn by an appliance is $I = \frac{P}{V}$ . Add the currents of everything switched on in one circuit and compare with its rating (5 A or 15 A).

Domestic Electric Circuits: formulas and key facts

Current drawn: $I = \frac{P}{V}$; V = 220 V for Indian mains.
Total current in a circuit (parallel): $I_{total} = I_{1} + I_{2} + \dots = \frac{P _{1} + P _{2} + \dots}{V}$; Must not exceed the circuit rating.
Maximum load: $P_{max} = V \times I_{rating}$; 5 A circuit: 220 × 5 = 1100 W; 15 A circuit: 3300 W.
Wire colours: $live: red; neutral: black; earth: green$; Live and neutral differ by 220 V.
AC in India: $220 V, 50 Hz; reverses every \frac{1}{100} s$; DC flows one way only.

How to solve Domestic Electric Circuits questions

For domestic circuit questions, decide whether it is about wiring, safety or a load calculation.

1Wiring: name live, neutral and earth with colours, and say appliances are in parallel.
2Safety: fuse (series; melts on excess current) and earth wire (low-resistance path for leakage).
3Fault: short circuit (live touches neutral) or overloading (voltage rise, too many appliances on one socket).
4Calculation: find each current with $I = \frac{P}{V}$ , add them, compare with the rating; or find maximum power $P = V I$ .
5State the result in words: the fuse will or will not melt, and why.
6For AC/DC, give direction behaviour, India's 50 Hz frequency, and the transmission advantage of AC.

Domestic Electric Circuits in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Overloading and fuse rating

Suppose on a cold evening your family runs a 2000 W room heater, a 1000 W electric iron and a 100 W fan on the same 15 A circuit, and then someone plugs in a second 1000 W heater on the same circuit.

Find the current before and after the second heater is switched on, and predict what happens. What should the family do instead?

Try it first, then show the solutionSolution

Before: total power = 2000 + 1000 + 100 = 3100 W; $I = \frac{3100}{220} \approx 14.1$ A, just under 15 A.
After: total power = 3100 + 1000 = 4100 W; $I = \frac{4100}{220} \approx 18.6$ A.
18.6 A is more than the 15 A rating: the circuit is overloaded, so the fuse wire heats up, melts and cuts off the supply.
Check: 15 A × 220 V = 3300 W is the maximum; 4100 W exceeds it.
They should not run so many high-power appliances on one circuit at the same time; switch one off or use another circuit.

Answer: About 14.1 A before (safe) and 18.6 A after; the 15 A fuse melts due to overloading. Spread the load or switch something off.

Memory hook: Add the watts, divide by 220, compare with the fuse.

Tricks to remember Domestic Electric Circuits

Short memory aids. Say each one aloud once, then use it on a question the same day.

Red is live danger, Green is ground
Red = live (danger), Black = neutral, Green = earth (grass on the ground).
Use it when: Wire colours.
Parallel = Private
Each appliance gets its own 220 V and its own switch.
Use it when: Why domestic wiring is parallel.
Short = Shake hands
Short circuit: live and neutral 'shake hands' directly.
Use it when: Defining short circuit.

Domestic Electric Circuits: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Earth wire · 2 marks · Very short answerBoard level

Explain the job done by the green earth wire, and why an electric iron or a refrigerator with a metal body must be connected to it.

Try it first, then show the solutionSolution

The earth wire connects the metallic body of an appliance to a metal plate deep in the earth, giving a low-resistance path for any leakage current (1 mark).
If current leaks to the metal body, its potential stays at that of the earth, so a person touching it does not get a severe shock (1 mark).

Answer: Low-resistance path to earth for leakage current, keeping the body at earth potential to prevent severe shocks.

Example 2: Oven on a 5 A circuit · 3 marks · Short answerHarder board level

An electric oven of 1.5 kW is operated on a 220 V domestic circuit of current rating 5 A. What result do you expect? Explain with calculation.

Try it first, then show the solutionSolution

$I = \frac{P}{V} = \frac{1500}{220} \approx 6.8$ A (1 mark).
This is more than the 5 A rating of the circuit (1 mark).
The circuit is overloaded: the fuse heats up, melts and breaks the circuit, so the oven stops working (1 mark).

Answer: The oven draws about 6.8 A > 5 A, so the fuse melts and the circuit breaks.

Example 3: How many bulbs? · 3 marks · Short answerHarder board level

How many 60 W bulbs can be safely run together on a 220 V, 5 A lighting circuit? Show working.

Try it first, then show the solutionSolution

Maximum safe power = $V I = 220 \times 5 = 1100$ W (1 mark).
Number of bulbs = $\frac{1100}{60} \approx 18.3$ , so at most 18 bulbs (1 mark).
Check: 18 bulbs = 1080 W, $I = \frac{1080}{220} \approx 4.9$ A (safe); 19 bulbs = 1140 W, $I \approx 5.2$ A (exceeds 5 A) (1 mark).

Answer: 18 bulbs.

Example 4: Short circuit vs overloading · 5 marks · Long answerHarder board level

Distinguish between short-circuiting and overloading. Give two causes of overloading and two precautions to avoid it. How does a fuse protect the circuit?

Try it first, then show the solutionSolution

Short-circuiting: the live and neutral wires come into direct contact (damaged insulation or faulty appliance), and the current increases abruptly (1 mark).
Overloading: the current exceeds the safe limit of the circuit (1 mark).
Causes of overloading: accidental hike in supply voltage; too many appliances connected to a single socket (1 mark).
Precautions: avoid connecting too many appliances to one socket; use fuses of correct rating; keep insulation in good condition (1 mark).
Fuse: a wire in series that melts by Joule heating when current is unduly high, breaking the circuit and stopping the excess current (1 mark).

Answer: Short circuit = live touches neutral; overloading = excessive current from voltage rise or too many appliances; fuse melts and breaks the circuit.

Example 5: Why parallel? · 3 marks · Short answerHOTS / competency

A student suggests wiring all the bulbs and fans of a house in series to save wire. Give three reasons why this would not work, using what you know about series and parallel circuits.

Try it first, then show the solutionSolution

In series, the 220 V would be shared among the appliances, so each would get less than its rated voltage and would not work properly (1 mark).
All appliances would carry the same current and switching off or failure of one would break the whole circuit, so they could not be used independently (1 mark).
Total resistance in series is the sum of resistances, so the current would be small and appliances of different power ratings could not each draw the current they need. In parallel, each gets 220 V and its own switch (1 mark).

Answer: Series would share voltage, prevent independent switching, and limit current; parallel gives each appliance 220 V and its own switch.

Where students lose marks in Domestic Electric Circuits

The slips examiners see most often, and what to write instead.

Mistake: Mixing up wire colours
Colours are learnt loosely.
Wrong working
Green insulation is the live wire.
Right working
Red is live, black is neutral, green is earth.
Do this: Use the memory trick.
Usually costs: 1 mark (also tested as a true/false item).
Mistake: Saying the earth wire carries the normal current
Students treat it as a third supply wire.
Wrong working
The earth wire carries current to the appliance.
Right working
It carries only leakage current to the earth, for safety.
Do this: Earth wire = safety path, not supply.
Usually costs: 1 mark.
Mistake: Confusing short circuit and overloading
Both make the fuse melt.
Wrong working
Short circuit means using too many appliances.
Right working
Short circuit = live and neutral in direct contact; too many appliances = overloading.
Do this: Learn the two definitions separately with their causes.
Usually costs: 1-2 marks.
Mistake: Wrong unit conversion for power
kW used as W.
Wrong working
2 kW oven: I = 2/220 A.
Right working
2 kW = 2000 W; I = 2000/220 ≈ 9.1 A.
Do this: Convert kW to W first.
Usually costs: The answer mark.

Exam tips

Draw the domestic circuit schematic: meter, main fuse, main switch, distribution with separate circuits, appliances in parallel, earth connection.
In calculations, show I = P/V, the total and the comparison with the rating.
Name two safety devices: fuse and earthing.
Give both causes of overloading as in NCERT.
The generator's working is formative-only; for AC, know 220 V, 50 Hz, reversal and the transmission advantage.

Practice questions on Domestic Electric Circuits

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The insulation inside a steel-bodied electric kettle wears through, so the live wire touches the kettle's body. Which part of the house wiring stops the person holding the kettle from getting a severe shock?
(a) the neutral wire (b) the earth wire (c) the main switch (d) the electricity meter
Hint
Which wire is joined to the metal bodies of appliances?
Answer
(b) the earth wire. It gives the leakage current a low-resistance path to the earth, so the metal body stays at the earth's potential.
Q2 · 1 mark · Assertion-reasonBoard level
Assertion (A): Domestic appliances are connected in parallel.
Reason (R): In a parallel arrangement, each appliance gets the same potential difference.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Why does each appliance need 220 V?
Answer
(a).
Q3 · 2 marks · Very short answerBoard level
Name the colours of insulation of the live, neutral and earth wires. What is the potential difference between live and neutral in India, and what is the frequency of the AC supply?
Hint
Recall the meter board.
Answer
Live: red; neutral: black; earth: green. Potential difference 220 V; frequency 50 Hz.
Q4 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose a family's kitchen circuit (220 V) is rated 15 A. They use a 1100 W microwave oven, a 1500 W induction cooktop and a 750 W mixer.
(a) Find the current drawn by the induction cooktop. (1 mark)
(b) Can all three run together safely? Show working. (1 mark)
(c) The cooktop has a metal body and a three-pin plug. Explain what the third pin is for and what could happen if it were broken. (2 marks)
Hint
Total power 3350 W.
Answer
(a) I = 1500/220 ≈ 6.8 A. (b) Total = 1100 + 1500 + 750 = 3350 W; I = 3350/220 ≈ 15.2 A, slightly above 15 A, so the circuit would be overloaded and the fuse could melt; they should not run all three together. (c) The third pin connects the metal body to the earth wire, giving a low-resistance path for leakage current so the body stays at earth potential. If broken, a leakage to the body could give the user a severe shock.
Q5 · 3 marks · Short answerHarder board level
What is the difference between direct current and alternating current? Give one source of each and one advantage of AC. How many times does the Indian mains current change direction in one second?
Hint
50 Hz: two reversals per cycle.
Answer
DC flows in one direction only (source: a cell or battery). AC reverses its direction periodically (source: mains supply). Advantage of AC: it can be transmitted over long distances without much loss of energy. At 50 Hz, it reverses twice per cycle, so 100 times each second (once every 1/100 s).
Q6 · 3 marks · Short answerHOTS / competency
A household's main fuse keeps melting whenever a particular old table fan is switched on, even when nothing else is running. Suggest the most likely fault and explain how it causes the fuse to melt. What should be done before the fan is used again?
Hint
A small fan alone cannot overload a circuit.
Answer
A fan alone draws a small current, so overloading is unlikely. The likely fault is a short circuit inside the fan or its cord, where damaged insulation lets the live and neutral wires touch. The current then increases abruptly, Joule heating melts the fuse and breaks the circuit. The fan's wiring and insulation must be repaired (or the fan replaced) before use.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Colour of earth wire?Show answer
Green.
2.Potential difference between live and neutral in India?Show answer
220 V.
3.Ratings of the two common domestic circuits?Show answer
15 A (high-power appliances) and 5 A (bulbs, fans).
4.How are appliances connected in a house?Show answer
In parallel.
5.What causes a short circuit?Show answer
Live and neutral wires coming into direct contact.
6.Frequency of AC mains in India?Show answer
50 Hz.

Domestic Electric Circuits: frequently asked questions

Why is an earth wire used?

It connects metal bodies of appliances to the earth, giving a low-resistance path for leakage current so users do not get a severe shock.

What is the difference between short-circuiting and overloading?

Short-circuiting is direct contact between live and neutral wires, causing an abrupt rise in current. Overloading is excess current due to a voltage rise or too many appliances on one socket.

Why are household appliances connected in parallel?

So that each gets the full 220 V and can be switched on or off independently.

What does a fuse do?

It is a wire in series that melts when the current is too high, breaking the circuit and protecting appliances and wiring.

What is the advantage of AC over DC?

AC can be transmitted over long distances without much loss of energy.