DIRECT-CUKRENT DYNAMOS AND MOTORS. 25 
20. Specific Cross-Section of Armature Conduc- 
tors.—It is customary to allow from 300 to 1,000 circular 
mils per ampere in armature conductors. The lower 
value applies to elevator motors and other machines that 
are used only intermittently, and seldom at full load, 
while the higher limit is for large machines running 
heavily loaded for long periods of time. An ordinary 
figure is 600 circular mils per ampere, which corresponds 
to a current density of about 2,000 ci per square 
inch of cross-section. 
One should be especially careful to ae correctly 
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Elect. Engineer Institute 
Fic. 18 —FLow or CURRENT IN Fia. 14.—FLOW OF CURRENT IN 
BIPOLAR ARMATURE. MULTIPOLAR ARMATURE. 
what fraction of the total current each conductor will have 
to carry, as follows: 
1. Ina bipolar machine there are two paths through the 
armature winding (Fig, 13), so that one-half of the total 
current flows through any given inductor. 
2. Ina multipolar machine with the -- and — brushes re- 
spectively connected in parallel (Fig. 14), or with cross- 
connected armature winding or commutator (Fig. 15, 
page 27), there are as many paths as there are poles, con- 
sequently the current in any conductor is the total amount 
divided by the number of poles. 
3. In a multipolar machine the armature is sometimes 
