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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
A. MICA PROPERLY UNDERCUT.
B. UNDERCUTTING TOOL TOO NARROW, LEAVING
FIN AT ONE SIDE OF SLOT.
C. UNDERCUTTING TOOL VERY NARROW, LEAVING
FINS AT BOTH SIDES OF SLOT.
D. SLOT IMPROPERLY INDEXED. PART OF BAR CUT
AWAY AND FIN OF MICA LEFT.
E. TOOL TOO WIDE. PART OF BAR CUT AWAY.
F. UNDERCUTTING T00 SHALLOW. SERVICE LIFE
SHORTENS BEFORE NEXT UNDERCUTTING.
G. UNDERCUTTING TOO DEEP. POCKET COLLECTS
CARBON AND COPPER DUST, SHORT-CIRCUITING
BARS.
Figure 4-20. Common undercutting mistakes.
e. Installation. One of the most important
ing of 230 volts will give reasonable performance
on: 220, 230 and 240-V systems. A motor with a
antifriction precautions for motors with ball or
roller bearings is to ascertain that the bearings are
single voltage rating of 230V will probably overheat
if run on 208V. Most manufacturers recognize this
properly installed. The inner race should be tight
enough on the shaft to rotate with it, but not so
problem and build extra capacity into the windings
tight as to cause frictional distortion. Ball or roller
to give a dual or triple voltage rating on the name-
bearings are normally lubricated with grease, and
plate, that is: 208/230/240 volts. There are some
cases where motors fail due to low voltage. If a
as in the case of oil lubricants mentioned above,
given motor is fully loaded or slightly overloaded, it
apply grease in accordance with the manufacture's
instructions.
will operate within its temperature limits for nor-
mal voltages. For voltages 90 percent and less of the
f. Vibration. Excessive vibration can loosen vari-
nameplate rating, the same motor will severely
ous parts, break electrical connections, crystallize
portions of the metallic structure and contribute to
overheat. The motor will fail if the low voltage con-
an increase in frictional wear. Checks should be
dition is applied for long periods of time. The impor-
made regularly to identify conditions that contrib-
tant thing to remember is that, in the example
ute to vibration such as misalignment, settling of
given above, a fully loaded motor must have 100
the foundation, heavy floor loading, and excessive
percent of its nameplate conditions in order to de-
bearing wear particularly when records indicate fre-
liver 100 percent of its capacity. A motor that only
equent motor failures. Check to determine whether
needs to deliver 80 percent of its nameplate horse-
vibration in the driven machine is being transmit-
power rating will most likely survive a prolonged
ted to the motor. Check that the motor is properly
low voltage condition resulting in a somewhat
applied for a particular load. Check for excessive
higher than normal temperature. This is sometimes
belt or chain tension. The trouble may lie in the
referred to as "service factor". Motor performance
push-apart effect inherent in spur gears. Check for
guarantee is based on its nameplate rating and not
motor-shaft oscillation resulting from a loose bear-
the system nominal voltage. The relationship be-
ing. Check for loose motor-mounting bolts.
tween the nominal and nameplate rating is shown
g. Applied voltages. For general purpose applica-
in table 4-2.
tions, a range of five percent under to five percent
h. Choice. There is usually some choice in the
over the nameplate voltage may be applied with
substitution of voltages for the motors and applica-
satisfactory results. A motor with a nameplate rat-
tions shown in table 4-2. It is not necessary to
4-23
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