Why Domestic Wiring Is in Parallel, Not Series | Class 10

Quick answer: Household appliances are connected in parallel so that each one gets the full mains voltage (220 V in the NCERT book), can be switched on and off independently, and keeps working if another appliance fails. In series, the voltage would be shared between appliances, the same current would flow through all of them, and one fault or switched-off device would stop everything.

Disadvantages of series connection in a house

 Live ─ bulb ─ fridge ─ heater ─ fan ─ Neutral
          (one single path)

1. Voltage is shared. In series, the supply voltage is divided among the appliances: $V = V_1 + V_2 + V_3 + \dots$. With four identical appliances, each would get only about 55 V, so none would work properly.
2. One fault stops everything. There is only one path for current. If one appliance fails or is switched off, the circuit breaks and all the others stop.
3. Same current through every device. Different appliances need very different currents, but in series they are all forced to carry the same current.
4. Large total resistance. $R_s = R_1 + R_2 + R_3 + \dots$, so the total resistance is high and the current is small.

Advantages of parallel connection

 Live ──┬─ switch ─ bulb ───┬── Neutral
        ├─ switch ─ TV ─────┤
        ├─ switch ─ heater ─┤
        └─ switch ─ fridge ─┘
   each branch gets the full voltage

1. Full voltage for every appliance. The potential difference across each branch equals the supply voltage, so each device works at its rated voltage.
2. Independent working. If one bulb fuses or is switched off, the other branches are not affected.
3. Separate switches. Each appliance can be controlled by its own switch.
4. Each appliance draws the current it needs. By $I = V/R$ (or $I = P/V$), a high-power appliance draws a large current and a low-power one draws a small current.
5. Lower total resistance. $\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$, so the equivalent resistance is less than the smallest single resistance.

How much current do appliances draw?

Using $I = P/V$ with $V = 220$ V:

These very different currents are only possible because the appliances are in parallel.

Note: NCERT uses 220 V for Indian household supply. The official standard is now 230 V, but use 220 V in exam answers unless the question says otherwise.

Why are some decorative lights in series?

Some strings of decorative lights use many small, low-voltage bulbs connected in series, so together they can run from the mains. For example, 88 bulbs rated at 2.5 V each add up to 220 V. The drawback is that if one bulb's filament breaks, the whole string may go dark. (Many modern strings use LEDs or have bypass arrangements to avoid this.)

Summary table

Exam tips

• For "disadvantages of series connection", give at least three: voltage divided, one fault breaks the whole circuit, same current through all.
• For "why parallel?", stress same voltage across each appliance and independent switching.
• Use $I = P/V$ to show that appliances need different currents.
• Draw a simple parallel circuit with a separate switch in each branch.

Common mistakes

• Saying the current is the same in a parallel circuit. It is the voltage that is the same; currents add up: $I = I_1 + I_2 + \dots$.
• Saying the voltage is the same in series. In series it is divided.
• Writing that parallel wiring increases total resistance. It decreases it.
• Giving unrealistic currents. Use $I = P/V$ to estimate them.

Frequently Asked Questions

Why are household appliances connected in parallel?

So that each appliance gets the full mains voltage, can be switched on or off independently, and keeps working even if another appliance fails.

What are the disadvantages of connecting appliances in series?

The supply voltage is divided among the appliances, the same current flows through all of them, and if one fails or is switched off, all the others stop working.

Is the voltage the same across all appliances in a parallel circuit?

Yes. Every branch of a parallel circuit has the same potential difference, equal to the supply voltage.

Why do some decorative lights go off when one bulb fails?

In strings where the bulbs are in series, there is only one path for current. If one filament breaks, the path is broken and all the bulbs go off.

What happens to total resistance when appliances are added in parallel?

The total resistance decreases, because 1/Rp = 1/R₁ + 1/R₂ + …, and is always less than the smallest single resistance.