Shunt Motors:

        Shunt dc motors, again similar to shunt generators, are
connected with the field windings and the armature windings in
parallel. In this case, the field windings carry only part of the 
excitation current, and are made of smaller-gauge wire than those
of a series motor. A shunt motor has good speed regulation, but
low starting torque. This is just the reverse of the series motor
characteristics. A shunt motor should not be used to start heavy
loads. It may, however, be allowed to run with no load because
speed depends primarily upon the resistance of th field windings.
By adding a variable resistance to the field coil circuit , motor
speed can be controlled above or below its nominal value. Increasing
the field resistance decreases the field current and the CEMF induced
in the armature. This causes greater current to flow through the 
armature, increasing the torque and the motor will speed up. 
Decreasing the field resistance causes the field current to increase,
increasing the CEMF developed in the armature, thus reducing armature
current. The reduced current produces less torque and the motor slows
down. Thus, the speed of a shunt dc motor is relatively independent
of the load.
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