The families at a glance
The register is divided the way the trade divides itself. Each family has its own way of putting insulation on a conductor, its own standards and its own route to the buyer.
| Family | How it is insulated | Specified by | Usually bought |
|---|---|---|---|
| Magnet wire | Enamel film, cured in an oven in many passes | NEMA MW 1000; IEC 60317 | Direct from the mill, by the pound |
| Building wire | Extruded PVC or cross-linked polyethylene | NEC types, listed to UL standards | Through electrical distributors |
| Flexible cord | Rubber or elastomer over fine strands | NEC Article 400 types, listed to UL 62 | As bulk cord or finished cord sets |
| High-performance wire | Fluoropolymer, polyimide or cross-linked thin wall | SAE, NEMA and military specifications | Through specialist distributors |
| Power and control cable | Extruded, cabled and jacketed; shielded at medium voltage | ICEA and NEMA standards, listed to UL | Direct or through distributors, by the reel |
Each family has a sheet in the register: magnet wire, building wire, flexible cord, high-performance wire and power and control cable.
What every mill shares
All of them start from copper or aluminum rod about the thickness of a finger. The rod is drawn through a series of dies, each a little smaller than the last, until it is wire of the right diameter. Drawing hardens the metal, so the wire is annealed to make it soft again. Fine wires are then twisted into strands. Up to this point a magnet wire mill and a building wire mill are doing recognizably the same thing, and some buy drawn or stranded conductor from each other or from a metals producer.
Where they part company
The difference is the insulation line, and it is expensive enough to decide what a company is.
Enameling builds a film in layers. The wire passes through resin and an oven a dozen times or more. A line is set up for a narrow range of sizes and one film chemistry, and changing either is a slow job.
Extrusion melts plastic and forms it around the conductor in one pass, at speeds that can exceed a mile of wire every few minutes for small building wire. It rewards enormous runs of a few products.
Cross-linking turns a meltable plastic into one that will not melt again. For building wire it is done chemically or with moisture; for thin-wall aerospace wire it is often done with an electron beam, which is a piece of equipment few companies own.
Fluoropolymer processing runs hot enough to need special alloys in the tooling, and PTFE cannot be melt-extruded at all. It is applied as paste or tape and sintered.
Medium-voltage extrusion applies three layers at once in a clean environment and cures them in a pressurized tube that can be several stories tall or hundreds of feet long.
A mill built around one of these does not drift into another. That is why asking a building wire maker for aircraft wire gets a polite referral, and why the register has five sheets where a single list would mislead.
Wire, cable, cord: the words
The trade uses the terms loosely, but there is a working distinction. A wire is a single conductor, bare or insulated. A cable is two or more insulated conductors under a common covering, or a single conductor large or complex enough to be called one. A cord is a cable built to be flexed in use. A cable assembly or harness is a different product again: cut wire with connectors fitted, made by an assembler and not by a mill. That work has its own guide at bestcablemfg.com.
Finding the family from a drawing
The callout usually gives it away. An MW number means magnet wire. A string of letters such as THHN or XHHW means building wire, and one such as SOOW means cord. A part number beginning with M and a slash, or an SAE AS number, means a military or aerospace wire. A reference to ICEA, or a voltage in kilovolts, means power cable. Reading a wire specification takes a callout apart piece by piece.