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A row of humps or a filled rectangle in a wire, marking an inductor.
Also known as: Coil symbol, Choke symbol, Humps symbol, Inductance symbol
An inductor is drawn as a series of humps in North American practice — a picture of a coil of wire — and as a filled rectangle under IEC practice. Like the resistor, the same component has two current and incompatible drawings.
Marks an inductor: a coil that stores energy in a magnetic field and opposes changes in the current through it.
Contexts: Electrical equipment
Is drawn in its common form as a picture of the component — a series of three or four semicircular humps standing for the turns of a coil.
Contexts: Electrical equipment
Appears under IEC practice as a plain filled rectangle instead, which carries no visual resemblance to a coil and is not interchangeable with the humped form.
As with the resistor, these are two conventions in simultaneous use rather than a symbol and its variant.
Contexts: Electrical equipment
Gains one or two parallel lines drawn alongside the coil where the inductor has a ferrite or iron core, which changes its behaviour substantially.
Contexts: Electrical equipment
Is drawn two different ways by two different standards. The international form defined by the IEC is a series of semicircular humps, or in some drawings a plain filled rectangle; the form defined by the American ANSI and IEEE standards is the same series of humps, drawn as a coil of wire seen from the side. Neither is a mistake and neither is old-fashioned — a reader meeting an unfamiliar drawing of a familiar component is usually looking at the other continent's standard rather than at an error.
Contexts: Technical drawing, Electrical equipment
Says what its core is made of by what is drawn beside it. A bare coil is air-cored; two solid parallel lines alongside mean an iron or ferromagnetic core; a dashed or broken line means a ferrite or powdered core. The core changes the inductance and the frequency the part is useful at, so the marking is not decoration.
Contexts: Technical drawing, Electrical equipment
Related forms that are not treated as separate canonical symbols — see our variant rules.
Iron-cored inductor
The coil with two solid parallel lines drawn along it, marking a ferromagnetic core.
Ferrite-cored inductor
The coil with a broken or dashed line along it, marking a ferrite or powdered-iron core.
Three or four semicircular humps in a row along a straight horizontal line, all bulging the same way, like a flattened coil seen from the side.
Both are passive components whose ANSI and IEC drawings diverge in the same way.