Clean the old insulation and varnish from the slots
before installing the new slot insulators. This cleaning
is usually done with a torch. The slot insulators are
formed from one of several types of material available
for this purpose. The best procedure is to reinsulate the
slots with the same type and size insulation that was
used in the original winding.
The coils are then wound according to the data sheet
and replaced in the slots in the same position as the
windings that were removed. The starting windings are
ALWAYS placed 90 electrical degrees out of phase with
the running windings.
When all the connections between the poles of the
windings have been completed and tested and the leads
attached, the stator should be placed in a baking oven at
a temperature of about 250°F and baked for three hours
to remove any trace of moisture. Heating the windings
also helps the varnish to penetrate the coils.
The stator is then dipped in a good grade of
insulating varnish, allowed to drip for about an hour and
then placed in the oven and baked for several hours.
When the stator is removed from the oven, the inner
surface of the core of the stator should be scraped to
remove the varnish so that the rotor will have sufficient
space to rotate freely.
Control for a Split-Phase Motor
The control switch for a split-phase motor is usually
a simple OFF and ON switch if the motor is equipped
with an overload device. If the motor does not have this
overload device, the switch will be of a type illustrated
in figure 7-33. This type of switch has two push buttons;
one to start and one to stop the motor. It uses
interchangeable thermal overload relay heaters for
protection of various size motors. In some cases, a 30-
ampere safety switch with the proper size fuse may be
The capacitor motor is similar to the split-phase
motor, but an additional unit, called a capacitor, is
connected in series with the starting winding, These
motors may be of capacitor-start or the capacitor-run
The capacitor is usually installed on top of the
motor; but it may be mounted on the end of the motor
Figure 7-33.Starting switch for a single-phase motor.
frame, or inside the motor housing, or remote from the
motor. Acapacitor acts essentially as a storage unit. All
capacitors have this quality and all are electrically the
same. The only difference is in the construction The
type of capacitor usually used in fractional-horsepower
motors is the paper capacitor. This type of capacitor has
strips of metal foil separated by an insulator, usually
waxed paper. The strips are rolled or folded into a
compact unit which is placed in a metal container either
rectangular or cylindrical in shape. Iwo terminals are
provided for connections.
The capacitor-start motor has, like the split-phase
motor, a centrifugal switch which opens the starting
winding when the rotor has reached the predetermined
speed, while the capacitor-run motor does not have the
centrifugal switch and the starting winding stays in the
circuit at all times. Figure 7-34 shows a capacitor-start
motor winding circuit. The capacitor motor provides a
higher starting torque with a lower starting current than
the split-phase motor.