e line, it is
quite obvious that the presence of the resistance and the impedance of
the armature winding would be objectionable if left in the circuit
through which the voice currents had to pass. For this reason, what is
termed an _automatic shunt_ is employed on generators designed for
series work; this shunt is so arranged that it will automatically
shunt or short-circuit the armature winding when it is at rest and
also break this shunt when the generator is operated, so as to allow
the current to pass to line.

[Illustration: Fig 74. Generator Shunt Switch]

A simple and much-used arrangement for this purpose is shown in Fig.
74, where _1_ is the armature; _2_ is a wire leading from the frame of
the generator and forming one terminal of the generator circuit; and
_3_ is a wire forming the other terminal of the generator circuit,
this wire being attached to the spring _4_, which rests against the
center pin of the armature so as to make contact with the opposite end
of the armature winding to that which is connected with the frame. The
circuit through the armature may be traced from the terminal wire _2_
through the frame; thence through the bearings to the armature _1_ and
through the pin to the right-hand side of the armature winding.
Continuing the circuit through the winding itself, it passes to the
center pin projecting from the left-hand end of the armature shaft;
thence to the spring _4_ which rests against this pin; and thence to
the terminal wire _3_.

Normally, this path is shunted by what is practically a short circuit,
which may be traced from the terminal _2_ through the frame of the
generator to the crank shaft _5_; thence to the upper end of the
spring _4_ and out by the terminal wire _3_. This is the condition
which ordinarily exists and which results in the removal of the
resistance and the impedance on the armature winding from any circuit
in which the generator is placed, as long as the generator is not
operated.

An arrangement is provided, however, whereby the crank shaft _5_ will
be withdrawn automatically from engaging with the upper end of the
spring _4_, thus breaking the shunt around the armature circuit,
whenever the generator crank is turned. In order to accomplish this
the crank shaft _5_ is capable of partial rotation and of slight
longitudinal movement within the hub of the large gear wheel. A spring
7 usually presses the crank shaft toward the left and into engagement
with the s