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How does an electric kettle work?

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Quick answer

An electric kettle uses a high-resistance heating element inside the water or under its floor. When you switch it on, current flows through the element, which heats up and transfers energy to the water by conduction. A bimetallic strip or steam sensor detects the steam from boiling water and automatically cuts the current, switching the kettle off.

An electric kettle boils water by passing electric current through a resistive heating element, usually hidden inside the base or under the floor of the kettle. A thermostat switches the current off automatically when steam reaches a bimetallic strip, so the water stops boiling soon after it starts.

Step by step

  1. You fill the kettle with water and place it on its base, which connects the heating element to the mains supply.
  2. Switching on completes the circuit, so current flows through the high-resistance element, making it hot.
  3. Heat passes from the element into the water by conduction, and the warmed water rises by convection, mixing the water.
  4. When the water reaches boiling point, steam rises and reaches a bimetallic strip or steam sensor near the top.
  5. The steam heats the bimetallic strip, which bends and trips a switch, cutting off the current to the element.
  6. The kettle stops heating, and the water cools down or stays hot depending on insulation and any keep-warm feature.

Key things to understand

  1. The heating element is a coil of high-resistance wire, often nichrome, that gets hot when current flows through it.
  2. Current enters through the base connector, flows through the element, and returns, completing a circuit.
  3. The element transfers heat to the water by conduction, and the water circulates by convection as it warms.
  4. When water boils, steam rises and reaches a bimetallic strip or steam sensor near the top or handle.
  5. The bimetallic strip bends, trips a switch, and cuts the current, so the kettle switches off automatically.

Labelled diagram

  1. Base connector

    Supplies mains electricity to the kettle through a cordless 360-degree plug.

  2. Heating element

    High-resistance wire that glows hot when current passes through it.

  3. Water

    Absorbs heat by conduction and circulates by convection as it warms.

  4. Steam sensor

    Bimetallic strip or electronic sensor that detects steam from boiling water.

  5. Switch

    Trips open when the sensor bends, cutting current to the element.

How an electric kettle boils water

Real-world examples

  • A standard plastic cordless kettle on a kitchen counter uses a concealed flat element under a stainless-steel plate.
  • A glass kettle with a blue LED light lets you see the element and the bubbling water as it boils.
  • A travel kettle with a dual-voltage switch works in countries with different mains voltages, such as the US 120 V and Europe 230 V.
  • A temperature-controlled kettle for tea or coffee lets you set the water to 80°C or 90°C instead of boiling.

Common mistake

✗ Myth: An electric kettle boils water by heating the metal body of the kettle, which then heats the water.

✓ Fact: The heating element itself gets hot and transfers heat directly to the water, either because it is immersed in the water or because it is clamped to a metal plate under the floor. The outer body stays relatively cool because it is designed to insulate and protect, not to heat.

People also ask

What causes the clicking sound when an electric kettle turns off?
The click comes from the switch mechanism snapping open. When steam heats the bimetallic strip, it bends and releases a spring-loaded contact. The spring forces the metal contacts apart quickly, producing a sharp click. That same click happens when you press the switch manually, because the same spring mechanism is used.
Why does an electric kettle sometimes not switch off?
If the steam sensor or bimetallic strip is coated with limescale or blocked, steam cannot reach it properly, so it fails to bend and trip the switch. A faulty switch or a kettle with a damaged steam tube can also stay on. In that case the water boils dry, and a secondary safety fuse may cut power.
Is it cheaper to boil water in an electric kettle or on a gas stove?
An electric kettle is usually more efficient because the element is in direct contact with the water, so almost all the electrical energy heats the water. A gas stove heats the pot and the surrounding air as well, losing more heat. However, the actual cost depends on local electricity and gas prices.
Why does an electric kettle switch off by itself?
A bimetallic strip or electronic steam sensor detects the steam produced when water boils. The steam heats the strip, which bends and pushes a switch contact apart, breaking the circuit. Once the current stops, the element cools and the strip returns to its original shape, ready for the next use.
Why does the outside of a kettle stay cool while the water boils?
The heating element is inside the water or in a metal plate under the floor, so most heat goes straight into the water. The outer body is made of plastic or a double wall that conducts heat poorly, and an air gap or vacuum between walls further slows heat loss, keeping the handle and sides safe to touch.
Does an electric kettle use a lot of electricity?
A typical kettle draws about 1,500 to 3,000 watts, which is high compared with many appliances. But it runs for only a few minutes, so the energy used is modest. Boiling more water than needed wastes energy, because the element heats every extra litre.
Why does limescale build up inside a kettle?
Tap water contains dissolved calcium and magnesium ions. When water boils, these ions react with bicarbonate to form insoluble calcium carbonate, which deposits as limescale on the element and inner walls. A thick layer insulates the element, making the kettle slower and less efficient.

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