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U.S. ELECTRICAL MOTORS
INSTALLATION AND MAINTENANCE
5. Reversing Rotation
The direction of rotation may be reversed by interchanging any two, of the three power phases to the motor
leads. Be sure that the power is off and steps are taken to prevent accidental starting of the motor before
attempting to change any electrical connections.
CAUTION
Some motors have unidirectional ventilating fans. Running such a unit in reverse for any extended
length of time will result in motor damage. On motors that are unidirectional, the direction of rotation
is noted by an arrow mounted above the take-off-shaft and by a warning plate mounted near the main
nameplate. To determine direction of rotation for which leads are connected, apply power momentarily
and observe rotation. Motor should be uncoupled from driven equipment to insure driven equipment
is not damaged by reverse rotation. Motor coupling may require removal or suppport if motor is
operated uncoupled from driven equipment.
6. Initial Start
After installation is completed, but before motor is put in regular service, make an initial start as follows:
A. Insure that motor and control device connections agree with wiring diagrams.
B. Insure that voltage, phase and frequency of line circuit (power supply) agree with motor nameplate.
C. Check insulation resistance according to Section Ill “Storage”, Part 3.
D. Check all foundation and base bolts to insure that they are tight.
E. If motor has been in storage, either before or after installation, refer to Section Ill “Storage”, Part 4 for
preparations.
F. Check for proper or desired rotation. See Part 5 of this section.
G. Insure that all protective devices are connected and are operating properly.
H. Run motor at minimum possible load long enough to be certain that no unusual condition develops.
Listen and feel for excessive noise, vibration, clicking or pounding. If any are present, stop motor
immediately. Investigate the cause and correct before putting motor into service. In the case of
vibration, see Part 7 of this section.
CAUTION
Repeated trial starts can overheat the motor (particularly for across-the-line starting)
or the external starting equipment. If repeated trial starts are made, allow sufficient
time between starts to permit heat to be dissipated from windings and controls to
prevent overheating. Refer to Starting Duty Nameplate (if supplied) and NEMA MG1-
12.54, MG1-20.42 and MG1-20.43 for allowable starting frequency and load inertia
(WR
2
).
Initial
Installation
8