Figure 7-54.Resistance reduced-voltage starter.
Part-winding starters use two magnetic starters and
operate like a resistance start controller. Figure 7-55 is a
schematic drawing of a wye-connected, three-phase
motor. The control circuits for the S and R relays are the
same as for a resistance reduced-voltage starter, and so
they are not shown. The S relay is energized first,
connecting voltage to only part of the winding. The
motor starts to run but develops little torque. At a
predetermined time, the R relay closes. This action
parallels the windings in the motor, reducing their
resistance and causing increased current flow and more
MOTOR MAINTENANCE, TESTING, AND
An electric motor must be checked, maintained, and
repaired just like any other piece of mechanical
equipment. With proper servicing, a motor will last
longer and give more efficient service. Included in
maintenance services are cleaning, lubrication,
ventilation, and testing.
Inspect motors internally and externally for foreign
materials, such as dust, dirt, corrosion, and paint. Open-
frame motors may be blown out with compressed air.
You should not apply too many coats of paint to motors.
A thick coat of paint will interfere with heat dissipation.
Figure 7-55.Part-winding starter.