MIL-DTL-68G
Shock. Fans shall withstand the shock tests specified in 4.6.11.
3.9
Airborne. Fans shall meet the A-weight sound level specified in 3.8.
3.10
Input variation. The power input of any individual fan in a lot shall not vary more than 15 percent
3.11
from the average obtained when tested as specified in 4.6.3.
3.12
Speed variation. The speed of any individual fan in a lot shall not vary more than 5 percent from
the average obtained when tested as specified in 4.6.2.
3.13
Output. The output shall be considered proportional to the thrust reaction of the fan, and shall be
in accordance with the limits specified in 3.8. The ratio of watts input over pounds thrust shall not exceed the
values specified in 3.8 at rated voltage.
3.14
Switch. The fan shall have a two or three position switch, as specified in 3.8, and shall be clearly
marked and designated by symbols. The switch shall be mounted as an integral part of the bracket assembly,
and when the fan is mounted on a bulkhead, the bracket assembly shall be located below the centerline of the
motor shaft.
3.15
Low speed. Where the fan is required to have two speeds (see 1.2 and 3.8), the low speed of the
fan shall be between 60 and 80 percent of the nominal high speed, when operated at the nominal operating
voltage.
3.16
Grounding. Each fan shall be designed such that an electrical conducting path shall exist between
exposed metal parts and the mounting bracket. The conducting path shall not use grounding wire except where
the grounding wire will not be subject to wear, fatigue or tension, and will not in any way interfere with proper
operation of the fan. The mounting bracket shall be grounded by a ground conductor which shall be one of the
conductors of the input cables.
3.17
Cable entrance. The design shall provide for entrance of the power cable from the front or sides of
the base; entrance of the power cable from the back of the base is not permitted. A cable clamp shall be
provided.
3.17.1
Cable clamp material. The cable clamp shall be made of malleable iron or sheet steel and shall be
treated to resist corrosion in accordance with MIL-E-917; or (for class 2 fans) shall be made of nonmagnetic
material; or shall be a nylon, snap-in, strain relief bushing.
3.17.2
Duty requirements. The cable clamp shall be sufficiently strong to adequately hold the power cable
withstanding a steady pull of 100 pounds for 5 minutes. The cable clamp shall not become loose under constant
strain, vibration or such changes in temperatures as may be encountered in service.
3.18
Life. Fans shall operate at rated voltage without defects or undue wear for the life period specified
in table I. At the end of the life period, the wear shall not exceed the following:
(a)
Commutator 0.030 inch in diameter.
(b)
Sleeve bearings 0.003 inch diameter.
(c)
Brushes shall not be worn to the extent of causing the fan to become inoperative during the life test
(see 4.6.10).
3.19
Dielectric. The insulation shall withstand the dielectric test specified in 4.6.4.
3.20
Insulation resistance.
3.20.1
Cold. The insulation resistance shall be at least 16 megohms when measured in accordance with 4.6.1.1.
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