Heaters and the home network

The main part of devices such as an electric kettle, iron, cooker or soldering iron is the heating element: a wire or ribbon in the form of a coil. Its operation rests on the Joule–Lenz law: when current flows, heat Q = I²Rt is released. For a heater a material with a large resistivity that does not melt or burn at high temperature is used (nichrome, ρ = 1.1 Ω·mm²/m); wire of small ρ such as copper would not heat enough. The coil is wound on heat-resistant insulation, so the hot part does not touch the body or the user. A soldering iron melts metal to join parts; in electric welding a huge current arc melts metal, which is very dangerous and is done only by a specialist in protective clothing. Children must not use such devices without an adult: they can burn and start fires.