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466 NOTES ON COPPER WIRE.
TABLE No. 86,—Sizes of Double Cotton=covered Copper
Wire (Magnet Wire).
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9 114 126 8.2 17 45 53 18.6
10 101 109 9.1 18 40 48 20.8
11 90 98 10 19 36 43 23.2
12 81 91 11 20 32 38 26.3
13 72 80 12.5 21 28 34 29.3
14 64 73 13.7 22 25 32 31.2
15 57 64 15.6 23 22 29 34.4
16 51 60 16.6 24 20 27 37
Example.
How many turns of No. 15 double cotton-covered wire will
go in one layer on a spool 5 inches long ?
Solution
:
In table No. 86 we find that for No. 15 double cotton- cov-
ered copper wire there are 15.6 turns per inch of spool; thus,
5 X 15.6 = 78 turns in 5 inches.
Enameled Copper Wire.
Enameled copper wire is insulated by multiple coats of
enamel. This insulation will not absorb moisture. It will stand
a higher temperature than cotton insulation, as enameled wire
will stand a temperature as high as 100° C, 212° F., without
injury.
Another great advantage of enameled wire is that the insu-
lation is so thin it does not add more than 1 to 2 mils to the
diameter of the bare wire. This is especially a valuable feature
for the smaller sizes of wire, because when a spool is wound with
a small size of double cotton-covered wire the insulation takes
up a large percentage of the space.
Carrying Capacity of Copper Wire.
When electricity is conveyed through a wire, it is always
necessary to select the size large enough to avoid undue heating.
The number of circular mils required for each ampere of
current will depend a great deal upon the facilities by which the
heat is conveyed away from the circuit.
Well ventilated armatures in small dynamos such as 2 horse
power or less may have 300 to 400 circular mils area in the wire
for each ampere of current they carry. Armatures in dynamos
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