Insulation of ordinary insulated wire is molded by extrusion technique, however, in case of magnet wire used for coils and or an electromagnets, from 0.002 mm to 0.05 mm extent of thickness is realized by coating technique.
In case of extremely small instrument of electronics, because usual plastic insulated wire cannot be used, there are cases that stranded magnet wire structure is wanted (required).
The product in this picture is one of those products. This wire is comprised of 7 conductor of 0.03 mm overall diameter Type 2 polyurethane coated copper conductor and twisted at 1 mm pitch. Therefore, when color of one center conductor is changed from others so that it can be discriminated from others, it becomes extremely thin shielded wire. (Note 1)
However, because tensile strength becomes extremely weak at this thiness, twisting technique becomes very hard.
Formal, enamel, polyester, polyurethane, etc. are used for the insulation material for magnet wire, because of soldering easiness, polyurethane is the most suitable for above applications.
Also, there are other method for magnet wires than coating, such as winding fiber of silk, cotton, glass, etc. and or combination of any of it with coating.
Note 1 - Coaxial Cable made by (of) Polyurethane coated twisted cable
When one center conductor is used for internal wire and external six conductor is used for shield conductor as coaxial cable, the following exlectrical characteristics is obtained:
| DC resistance | 30 Ω/m |
|---|---|
| Characteristic impedance | 40 Ω |
| Velocity ratio | 0.7 |
| Attenuation constant | 7e-5*sqrt(f) neper/m (f = frequency in Hz) |
| Capacitance | 120 pF/m |