22 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
good insulating material, but cannot stand medium or higu 
temperature, as it becomes soft at about 180 degrees Fahr. 
44. Insulation of Coils.—The coils when projecting out of 
the armature are wound in such a manner as to prevent. 
a breakdown between ‘any coil of one phase and any coil 
of another, or between any coil of any phase and the frame 
of the machine. For the first purpose, safe distances are 
to be kept between the end connections of the coils, which 
are taped over and varnished. ; 
In high tension machines it is essential to have a safe dis- 
tance between the live copper and the iron. As an addi- 
tional safeguard it is well to cover the iron opposite the 
eoils with cloth and varnish, for example, in a 6,000 volt 
machine a distance of about 2 inches between any two 
coils of two different phases and 2.5 inches between the 
well insulated copper windings and cloth covered iron, is 
to be provided. 
45. Insulation of Armature Conductors.—The proper 
insulation of the armature conductors also requires careful 
attention on part of the designer. It is best to cover 
conductors of large section. with oil linen, which ean be 
done on ordinary taping machines. For wires used in’ 
TABLE 6.—INSULATION THICKNESSES OF ROUND 
WIRES AS USED FOR LOW TENSION. 
One Cotton Covering and 
Double Cotton Covering. One Braiding 
.008 inch. .027 inch. 
[O10 ss .030 ** 
Bi Oh lobe t ae, 3 
re Os slams. 
medium or high pressure machines the insulation material 
adopted is cotton. For medium pressures the conductor 
receives a double or single covering and one braiding. 
Table 6 indicates the usual thicknesses of double. covering 
and braiding as used for low tension work. 
