MIL-DTL-25038J
4.6.11 Wicking. A specimen of each finished wire size to be tested shall be cut 6±.0625 inches
(152±1.59 mm) with square ends. The specimen shall be vertically immersed for 2 inches (50.8 mm) of
its length in medium dry, red instrument ink (see 6.8) or equivalent, which is contained in an open test
tube, and conditioned for 24 hours at room temperature in a draft-free room. After this conditioning, the
ink on the surface shall be removed immediately from the 2 inches (50.8 mm) immersed by wiping gently
with a clean, dry lint-free cloth. The specimen shall then be examined for wicking between insulation
layers. The distance that the ink has wicked above the immersed portion of the specimen shall be
measured as the distance of wicking.
4.6.12 Thermal shock.
4.6.12.1 Preparation of specimen. A specimen of wire 5 feet long shall be prepared by carefully
removing 1 inch (25.4 mm) of insulation from each end of the wire. (For purposes of this test, insulation is
defined as all layers of non-conducting material covering the electrical conductor, e.g., primary insulation,
all tapes and braids, and jacket.) A razor blade, or equivalent, held perpendicular to the axis of the wire,
shall be used to cut the insulation for the removal operation. The length of exposed conductor at each
end of the specimen shall be measured to the nearest .01 inch (.254 mm). The specimen shall be formed
into a loose coil not less than 1 foot in diameter and shall be laid on a wire screen for handling throughout
the test.
4.6.12.2 Test procedure. The specimen shall be placed for 30 minutes in an air-circulation oven,
preheated to 500±4 °F. The specimen shall then be removed from the oven and within 2 minutes shall be
placed in a chamber that has been pre-cooled to -67±4 °F. The specimen shall be exposed to this
temperature for 30 minutes, after which the specimen shall be removed and allowed to return to and
stabilize at room temperature, 68 to 77 °F. At the conclusion of this cycle, the distance from the end of
each layer of insulation to the end of the conductor shall be measured to the nearest .01 inch (.254 mm).
This thermal shock cycle and the measurements shall be repeated for an additional three cycles (a total
of four cycles). Any measurement varying from the original measurement by more than that specified in
the applicable specification sheet shall constitute failure.
4.6.13 Insulation flaws. One hundred percent of the finished wire shall be tested using the spark test
or impulse dielectric voltage test to determine the presence of insulation flaws. Any portion of the wire
failing this test shall be cut out of the finished wire before final spooling.
4.6.13.1 Spark test. The finished wire shall pass through a suitable spark-test device that shall give
intimate metallic contact with practically all the wire insulation surface and expose the insulation to an ac
potential of 2,500V rms at 60Hz or 3KHz, in accordance with NEMA-WC 56. Electrode length and speed
of wire through the electrode shall be such that the insulation shall be subjected to the test voltage for a
minimum of .2 seconds.
4.6.13.2 Impulse dielectric test. The finished wire shall be tested in accordance with MIL-STD-2223,
method 3002 at 5000V (peak).
4.6.14 Marking durability. The durability of product identification or color markings applied to the wire
for coding shall be evaluated at 68 to 77 °F as follows:
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