MIL-DTL-24643C
The gas exiting the burner shall then be ignited and the air flow to the burner adjusted to produce the smallest
blue flame possible. The short circuit monitor test voltages shall then be applied to the specimen, as shown on
figure 11. If the specimen is armored, an additional test voltage shall be applied by grounding the armor as shown
on figure 11. (This will effectively apply an additional voltage which is approximately equal to the test voltage
divided by the square root of three between the armor and the specimen conductors.) The flame and test voltages
shall remain continuously applied to the specimen for a period of not less than that specified (see 3.1), unless
specimen failure (see 4.8.14.4) occurs prior to the end of this period, in which case the test may be terminated.
4.8.14.4 Observation. Specimen failure shall be construed in any fuse blows or if any overload relay trips prior
to completion of the specified test period (see 3.1).
4.8.15 Heat distortion. This test shall determine the ability of insulation and jacket material to resist physical
deformation when subjected to an elevated temperature.
4.8.15.1 Specimen. Each specimen shall be removed from completed cable in accordance with a and b, (1) or
(2), whichever is indicated. The number of specimens which shall be required shall be in accordance with b(3), (4),
or (5), as appropriate.
a. Cable jacket. Each specimen shall consist of a piece jacketing that has been removed from a finished cable
and a cut to form rectangular strip. This strip shall be not less than ⅞ inch long nor less than 9/16±1/16 inch wide, and
shall be ground and buffed to a thickness of 0.050±0.010 inch with a grinding apparatus (see 4.8.15.2.c). The
thickness of the specimen shall be made as uniform as practicable.
b.
Insulation.
(1) Cables which incorporate conductors with cross-sections of more than 190,000 circular mils, each
specimen shall consist of a piece of insulation which has been removed from a conductor and which has been cut to
form a rectangular strip. This strip shall be not less than ⅞ inch long nor less than 9/16±1/16 inch wide, and shall be
ground and buffed to a thickness of 0.050±0.010 inch with a grinding apparatus (see 4.8.15.2.c). The thickness of
the specimen shall be made as uniform as practicable.
(2) Cables which incorporate conductors with cross-sections of 190,000 circular mils or less, each
specimen shall consist of a single insulated conductor of a length not less than ⅞ inch. NOTE: In order to prevent
misleading results, the conductor should be removed and replaced with a solid copper rod of similar diameter.
(3) Cables containing four or fewer conductors, one specimen shall be prepared from each insulated
conductor.
(4) Cables containing more than four but fewer than 21 conductors, one specimen shall be prepared from
each of four different insulated conductors (a total of four specimens).
(5) Cables containing 21 or more conductors, the number of specimens prepared shall be equal to the
square root (rounded if necessary, to the nearest whole number) of the total number of conductors. Each specimen
shall be prepared from a different insulated conductor.
4.8.15.2 Special apparatus. Apparatus shall include the following:
a. A self standing thickness gauge, for supporting the requirements as specified in 4.8.15.3, which shall
exhibit a measurement error of not less than ±0.001 inch. This gauge shall incorporate a flat horizontal plate upon
which the entire specimen shall be laid flat during measurement and shall incorporate a foot which rests upon the top
of the specimen during measurement. This foot shall be attached to a plunger which moves freely in the vertical
direction and which is attached to a dial or other indicating device from which the specimen thickness may be read.
The foot shall present a horizontal disk of ±1/64 inch diameter to the specimen, which shall bear down on the
specimen with a force of 85±4 grams and shall be loaded with weights (see 4.8.25.3) to present additional force to
the specimen.
b. A micrometer (required for insulated conductor specimens only) with flat, parallel measurement surfaces
on both spindle and anvil, for the specimen thickness measurement as specified in 4.8.15.3.b(1), which shall exhibit
a measurement error of not more than ±0.001 inch.
c. A motor driven grinding wheel and a motor driven buffing wheel, or their equal, for the specimen
preparation as specified in 4.8.15.1.a and b(1). Guides shall be provided to assure that the specimen is pulled
tangentially to the surface of each wheel during grinding and buffing.
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