3.1.15 Compound-wound motor. - A compound-wound motor is one which has two separate field
windings: one, usually the predominating field, connected in parallel with the armature circuit, and
the other connected in series with the armature circuit.
3.1.16 Efficiency. - The efficiency of a motor is the ratio of the useful power output to the total
3.1.17 Direct measured efficiency. - The output is determined by direct measurement of torque
3.1.18 Conventional efficiency. - The output is determined by subtraction of the component losses
from the input.
3.1.19 Thermal protective (inherenting overheating protective device). - A thermal protector is a
protective device which is responsive to motor current and temperature whose purpose, when applied to
a motor, is to protect the motor against excessive overhearing due to overload or failure to start.
3.1.20 Integral horsepower-motor. - An integral horsepower motor is one built in a frame size 203
or larger as shown in table B of figure 1 or table for d. c. motors of Specification MIL-I-17840,
3.1.21 Set. - The word "set" as applied to any particular item in the list of repair parts and tools
means the total number of such parts incorporated in the construction of one motor.
3.1.22 Service A. - A service "A" motor is a high grade, class HI shockproof motor meeting the
requirements specified in 3.1 to 3.6.1 inclusive (see 6. 1).
3.1.23 Service C. - A service "C" motor is a marine type commercial motor meeting the require-
ments specified in 3.1 to 3.5.2 inclusive and 3.6.2 (see 6.1).
3.1.24 Speed regulation. - The speed regulation of a motor is the change in speed when the load is
reduced from full load (hot) to no load (hot) with constant applied voltage and field rheostat setting,
expressed as a percent of rated full load (hot) speed.
3.2 General design. -
3.2.1 Ambient temperature. - Motors shall be designed for the following ambient tern peratures as
specified (see 6.2):
40°C - - - - - - - - - 65°C.
50°C - - - - - - - - - Special
3.2.2 Audible noise. - Motors shall operate without objectionable audible noise at al loads and speeds
within the service range. where specified (see 6. 2), specific limits on the audible noise produced by the
motor shall apply.
3.2.3 Voltage limitation. Motors shall be designated for the following voltages as specified (see 6. 2): For
submarine voltages, see 184.108.40.206.
3.2.4 Voltage limitation. - Except for submarine service (see 3.7. 1), motors shall operate suc-
cessfully at rated load with voltage not more than 10 percent above or below rated voltage, but not
necessarily in accordance with the standards of performance established for operation at rated voltage.