Electric kettles are normally constructed of durable plastic or steel (with a plastic handle) and powered by mains electricity.
In modern designs, once the water has reached boiling point, the kettle automatically deactivates, preventing the water from boiling away and damaging the heating element. A bimetallic strip thermostat is commonly used as the automatic shut-off mechanism. The thermostat is isolated from the water in the kettle and is instead heated by the steam created when the water boils, which is directed through a duct onto the bimetallic strip. This allows the thermostat to be coarsely calibrated, which in turn allows the kettle to function normally at a wide range of altitudes. A consequence of this design is that the kettle may fail to deactivate if the lid is left open, due to an insufficient amount of steam being ducted onto the bimetallic strip.
Electric kettles were introduced as means to boil water without the necessity of a stove top.