Specifications

19
Table 2.2 showing increase in dimensions due to enamel (synthetic) covering
Grade of covering Minimum increase (mm) Maximum increase (mm)
Fine 0.035 0.060
Medium 0.060 0.100
Thick 0.100 0.150
2.6 PROPERTIES OF ENAMELLED WIRES : Excellent dielectric strength. Very low dissipation
factor, remaining reasonably constant at high frequencies or under humid conditions. No
mechanical or chemical stripping required. Adequate ventilation required when tinning or soldering.
Thermoplastic flow temperature not less than 320ºC, Smooth Glossy surface finish, Chemically
very stable, resists extraction with R22, methanol trichloroethylene and perchlorethylene. Usable
in hermetically sealed coils Excellent stability with a heat shock of not less than 205ºC. Good
resistance to abrasion. Good flexibility and adhesion to the conductor Smaller coefficient of
friction, Higher mechanical intensity, Excellent heat resistance. Good solderability.
Limitations : Insulation properties downgraded over 200ºC. Prone to hydrolysis if used in hermetic
systems or encapsulations when in the presence of cellulosic materials or moisture. Prolonged
contact with aggressive solvents (e.g. keytones, alcohol) may cause enamel softening.
2.7 TYPES AND SHAPES OF WINDING WIRES: The winding wires used in electrical motors
are classified as follows. 1) Round wires 2) Rectangular straps 3) Stranded wires
1. Round Wires: It has thin and thick conductors and are used in semi-closed slot type motors
and mush winding rotors. It is wounded in reels and available in Kilograms.
2. Rectangular straps: It is used in open type slot motors. These conductors are available as
long straps in meters. They are used in the following places. 1) Low voltage motor windings.
2) Used as conductor in high current motor. 3) Series field motor winding coils.
3. Stranded wires: Stranded wire is composed of a bundle of small-gauge wires to make a
larger conductor. Stranded wire is more flexible than solid wire of the same total cross-sectional
area. Stranded wire is used whenever ease of bending or repeated bending are required. Such
situations include connections between circuit boards in printed-circuit-board devices, where
the rigidity of solid wire would produce too much stress as a result of movement during assembly
or servicing; A.C. line cords for appliances; musical instrument cables; computer mouse cables;
welding electrode cables; control cables connecting moving machine parts; mining machine
cables; trailing machine cables; and numerous others. 1) Cotton covered insulating wire
2) Silk covered insulating wire 3) Paper insulated wire 4) Varnish coated glass paper covered
wire 5) Enamel coated round shaped wire.
Note: Usage of alternate sizes
1. If rewinding is done, use the existing winding wire gauge number for the new winding.
Sometimes if same gauge winding wire is not available then we can use the 2 runs of
wire each having half of the area of cross section of the original one.