3.3.21 Motors. Motors shall be in accordance with MIL-M-17060 for alternat-
ing current (at) motors and shall be of the following characteristics:
See 3.3.21.1.
Horsepower
A.
Service
Constant.
Speed classification
Continuous.
Duty
Totally enclosed or dripproof
Enclosure
In accordance with FF-B-171:
Bearings
MIL-B-17931 if low noise application.
50
Ambient temperature
B or F, with sealed insulation
Insulation
system, or class H.
Type
Squirrel cage induction, wye-delta
(see 6.2).
Unless otherwise specified (see 6.2),
Voltage rating
440 volts ac, 3-phase.
As required (see 3.3.23).
Design
As specified (see 6.2).
Low noise insulation
3.3.21.1 Horsepower rating. The horsepower rating of each motor shall be
not less than the sum of the maximum brake horsepower of the driven components
under any condition of service. The actual motor rating shall be in accordance
with MIL-M-17060
If the maximum brake horsepower of the equipment is less than
2, and if there is a possibility of an unpredictably high frictional load due to
an improper adjustment of glands or to some other cause, then the maximum brake
horsepower shall be multiplied by a safety factor of 1.5-maximum brake horse-
power/4 before selecting the next larger Navy standard rating.
3.3.21.2 Thermal protection. Thermal protection shall be provided for the
purifier motor stator and motor bearings in accordance with MIL-M-17060, with the
provision for de-energizing the motor control. Thermal protection for motor
bearings and motor stator shall be in parallel electrically. The thermal
protection shall include motor-mounted monitor control with a plug-in relay having
not less than one pair of normally open and one pair of normally closed contacts.
The temperature sensing system shall include not less than three thermal sensors
imbedded in the stator windings and one thermal sensor for each motor bearing.
Positive temperature coefficient (ptc) thermal sensors shall be used and shall
have a temperature coefficient of resistance at the switchpoint of not less than
15 percent per degree Celsius.
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