MIL-DTL-24643C
4.8.16.2 Special apparatus. Apparatus shall include a tank which can be filled with water, can be internally
pressurized to the specified value (see 3.1) and which is used for applying this water pressure to one specimen end,
as specified in 4.8.16.3. An appropriate stuffing tube shall be welded into the tank wall to provide a means for
sealing the one specimen end within the tank. An appropriate packing assembly shall be available to affect this
sealing (4.8.16.3). A means shall be provided whereby the pressure within the tank can be measured within an
accuracy of ±5 percent.
4.8.16.3 Procedure. One end of the specimen shall be installed through the tank stuffing tube and shall be
sealed in place by using a cable packing assembly. The opposite specimen end shall remain freely exposed to air for
the remainder of the test. The tank shall then be closed and filled with water such that the specimen end within the
tank remains directly and entirely exposed to water for the remainder of the test. The water shall then be pressurized
to a value of not less than that specified (see 3.1). This pressure shall be maintained for a continuous period of not
less than that specified (see 3.1), unless specimen failure (see 4.8.16.4) occurs prior to the end of this period, in
which case the test may be terminated prematurely. Following the test, the specimen shall be removed from the tank
and the end which had been exposed to water pressure shall be examined.
4.8.16.4 Observation. Either of the following shall constitute specimen failure:
a. Any water leakage from the free end of the specimen in excess of that specified (see 3.1) at any time during
the test.
b. Slippage of more than ¼ inch, with respect to the specimen jacket, of any specimen component at the end
of the specimen which had been exposed to water pressure.
4.8.17 Permanence of printing (conductor insulation). This test shall determine the ability of printed
information on insulated conductors to remain legible in the presence of repeated abrasion.
4.8.17.1 Specimen. Each specimen shall consist of a single insulated conductor which shall have sufficient
length for use in the test as specified in 4.8.17.3. Specimens shall be removed from completed cable as follows:
a. Cables containing four or fewer conductors: one specimen shall be removed from each insulated
conductor.
b. Cables containing more than four but fewer than 21 conductors: one specimen shall be removed from each
of four different insulated conductors (a total of four specimens).
c. Cables containing 21 or more conductors: The number of specimens removed shall be equal to the square
root (rounded, if necessary, to the nearest whole number) or the total number of conductors. Each specimen shall be
removed from a different insulated conductor.
4.8.17.2 Special apparatus. Apparatus shall include an abrading machine, which shall secure a specimen
horizontally between two fixed supports, and which shall abrade the specimen printed identification by means of a
motor-driven, reciprocating tape consisting of number 50-2/20 unbleached cotton braid. One possible arrangement
for the abrading machine is shown on figure 12. The braided cotton tape shall lie flat on the specimen surface, shall
remain perpendicular to the specimen axis, and shall abrade an unchanging area of the specimen periphery, over an
arc of not less than 135 degrees, at all times during the test. One end of the tape shall be reciprocated at a rate of
28±3 cycles per minute, such that the tape is drawn across the specimen for a distance of 10 plus 1, minus 0 inches
in each direction (20 inches minimum total excursion during cycle). The opposite end of the tape shall be
maintained under tension by a freely suspended ½+1/64, -0 pound weight. Each side of the tape shall be used to
perform not more than 500 cycles; the tape shall then be discarded and replaced. The abrading machine shall
incorporate an automatic counter to total the number of abrasion cycles to which the specimen is subjected during
the test.
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