n the
comparison is made with double silk insulation or with cotton
insulation. Again, where it is desired to reduce the winding space and
keep the same number of turns, an equal number of turns may be had
with a corresponding reduction of winding space where enameled wire is
used in place of silk or cotton.

In the matter of heat-resisting properties the enameled wire possesses
a great advantage over silk and cotton. Cotton or silk insulation will
char at about 260 deg. Fahrenheit, while good enameled wire will stand
400 deg. to 500 deg. Fahrenheit without deterioration of the insulation. It is
in the matter of liability to injury in rough or careless handling, or
in winding coils having irregular shapes, that enamel wire is
decidedly inferior to silk or cotton-covered wire. It is likely to be
damaged if it is allowed to strike against the sharp corners of the
magnet spool during winding, or run over the edge of a hard surface
while it is being fed on to the spool. Coils having other than round
cores, or having sharp corners on their spool heads, should not
ordinarily be wound with enamel wire.

The dielectric strength of enamel insulation is much greater than that
of either silk or cotton insulation of equal thickness. This is a
distinct advantage and frequently a combination of the two kinds of
insulation results in a superior wire. If wire insulated with enamel
is given a single wrapping of silk or of cotton, the insulating and
dielectric properties of the enamel is secured, while the presence of
the silk and cotton affords not only an additional safeguard against
bare spots in the enamel but also a certain degree of mechanical
protection to the enamel.

Winding Methods. In winding a coil, the spool, after being properly
prepared, is placed upon a spindle which may be made to revolve rapidly.
Ordinarily the wire is guided on by hand; sometimes, however, machinery
is used, the wire being run over a tool which moves to and fro along the
length of the spool, just fast enough to lay the wire on at the proper
rate. The movement of this tool is much the same as that of the tool in
a screw cutting lathe.

Unless high voltages are to be encountered, it is ordinarily not
necessary to separate the layers of wire with paper, in the case of
silk-or cotton-insulated magnet wire; although where especially high
insulation resistance is needed this is often done. It is necessary to
separate the successive layers of a magnet th