Parallel Circuits — Why Every Appliance Gets the Full 230 V
The core idea
In a series chain, one current squeezes through every element in turn, and the supply voltage divides among them. In a parallel circuit, every branch is wired straight across the same two supply rails — so every branch sees the full voltage, and the currents simply add up.
Each branch obeys Ohm's law independently (I = U / R), so the total current drawn from the supply is I_total = I₁ + I₂ + … Each added branch makes the source work harder, which shows up as a smaller total resistance. Two resistors in parallel combine as:
1/R_total = 1/R₁ + 1/R₂, or for the everyday two-resistor case, R_total = R₁·R₂ / (R₁ + R₂) — "product over sum".
The result is always lower than the smaller of the two resistances. A 10 Ω and a 30 Ω in parallel give 7.5 Ω, not 20 Ω — the big resistor opens a second lane for current rather than choking the first one. That is the entire point of how buildings are wired: one lane per appliance.
Real-world example
Walk into any kitchen. The kettle (≈10 Ω heating element) and the toaster (≈30 Ω) are both plugged into the wall — both in parallel, so both enjoy the full 230 V and run at their rated power simultaneously. The kettle pulls 23 A, the toaster 7.7 A, so the supply delivers about 30.7 A and roughly 7 kW of heat between them. That is precisely why a weak extension lead or a tired socket contact serving both can overheat: the wiring, not the physics, is the limit. It is also why one blown bulb in a parallel-wired room leaves the others shining — each branch lives or dies on its own path.
Common pitfall
Treating parallel resistance like a simple average — or assuming adding a resistor must raise the total. Adding a branch always lowers total resistance and raises total current. An electrician sizing a circuit cares about the sum of the appliance currents, because that — not the resistance — is what heats the cable and trips the breaker.
Series (electrotechnics L1 extension) vs parallel, in one line: series shares the voltage and the current is common; parallel shares the current and the voltage is common.