Split-Phase Inductor Motors:

        A split-phase inductor motor produces a rotating field in the same
way that a two or three-phase motor does. A separate stator winding, called
a Starting Winding, is included in the stator field. This winding
has only a few turns of very light gauge wire. When the ac line is applied
to both windings simultaneously, a field builds up much more quickly around
the starting coil than around the main coil. That is, the field around the
main windings Lags the field around the starting coil. This produces
a partially-rotating stator field, which starts the motor. Once the motor
is running, the starting winding must be removed from the circuit. Since
the coil is light, continuous current through it would cause the winding
to burn out. One widely used method for doing this is to use a Centrifugal
Switch physically mounted on the rotor, and wired in series with the 
starting coil. When the rotor gains sufficient speed to continue turning,
using only the main field, centrifugal force operates the switch contacts,
and breaks the starter coil circuit.

Split-Phase Capacitor Motors:

        Split-phase capacitor motors also produce a partially rotating
stator field. In this case, however, the starting winding need not be a
light coil. A large capacitor is placed in series with the second winding.
When the line current is applied, a field builds up around the starting
winding earlier than around the main winding. The main winding field
LAGS that of the starting winding. Since the phase shift results from the
capacitor, the starting coil may be identical to the main winding, and left
in the circuit at all times. When this is done, the motor is called a 
Capacitor-run motor. If instead, a lighter coil is used, and should
not be left in the circuit, a centrifugal switch is used to break the series
circuit after the motor has reached starting speed. This type of motor is
called a Capacitor-start motor.
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