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Enameled wire is often used in magnets, speakers, and electric motors. In place of a plastic or rubber coating, this wire is simply painted with a protective coating that often doubles as a flux coating. This eliminates the need to strip the wire free of the coating before soldering it. The type of enamel, as well as its thickness, is used to designate the grade of one, two, or three, with three being the highest grade of insulating properties. Copper and aluminum wires can both be enameled, as can round and rectangular wire that is often used in motor winding in order to make the most of the limited space.
Polyurethane, polyamide, or polyester resins are used to coat the wire instead of paint, as the name might suggest. This coating, while insulating, often has a sticky feel to it when touched. The coating is resistant to heat and high voltage, and the thickness of the wire is directly related to the thickness of the enamel coating that is applied to it. It is not uncommon for enameled wire to be used inside of transformers because of its high temperature rating. The coating used on newer wire is a flux-like product that can be soldered without requiring the enamel to be stripped off.
Some older wire of this type does not have the flux-like coating, so users should clean it before soldering. This can be accomplished by sanding the enamel off of the wire using sandpaper. Most of the enamel-coated wire is red, green, or brownish in color, with the color being associated only with the type of coating the wire has. There is typically no significance in wire coating color as far as heat resistance, type of wire, or intended use is concerned.
The classification of enameled wire is based on heat or temperature, and the expected lifetime of the wire at a given temperature. Typical temperature ratings are based on a 20,000-hour service life at a given temperature, with an increase in lifespan for operating at a lower heat. The most common shape is round, but rectangle shaped wire is commonly used in electric motors where space is at a premium — it can be wound more tightly and with less space between windings. This allows the most efficient use of the space available inside of the motor cases.