MIL-DTL-24643C
4.9.4.2 Observation. Specimen failure shall be construed if any specimen conductor exhibits a conductor
resistance greater than that specified (see 3.1).
4.9.5 Insulation resistance. This test shall determine the ability of completed cable to transmit DC without
exhibiting unacceptable current flow through insulation or jacketing material, either between conductors, or between
single conductor cables and any conducting substance which may be in contact with the surface of the cable during
in service use. The voltage withstand test (see 4.9.8) shall be performed prior to the insulation resistance test.
4.9.5.1 Selection of insulated conductors. The conductor insulation resistance test shall be performed on all
conductors which have a nominal circular mil area of less than18 AWG; for conductors which have a nominal
circular mil area of 18 AWG or greater, the conductor insulation resistance test shall be performed on conductors
selected as follows:
No. of insulated conductors
No. of insulated conductors
in cable
selected for test
1 through 4
All
5 through 20
4
21 through 30
5
31 through 42
6
43 through 56
7
57 through 72
8
73 through 91
9
92 through 110
10
111 through 132
11
133 through 156
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4.9.5.2 Specimen. The specimen shall be that which was previously used to perform the voltage withstand test
(see 4.9.8.1).
4.9.5.3 Special apparatus. Apparatus shall include the following:
a. A megohmmeter, megohm bridge or other suitable instrument which shall use a DC test voltage of not less
than 200 V nor greater than 500 V, which shall support the requirements as specified in 4.9.5.4, and which shall
make measurements within an accuracy of ±10 percent.
b. Water tank [may not be required, (see 4.9.5.4.e)] which shall be of a size to contain the specimen, and
which shall be suitable for the use as specified in 4.9.5.4.e.
4.9.5.4 Procedure. The specimen shall be maintained at a constant temperature, within ±3 °C, for a period of
not less than 5 hours immediately prior to testing. This temperature shall be noted and shall be used to calculate F
(see formula below) when measurements are made in accordance with a, b, or c. The megohmmeter shall then be
electrically connected to specimen as specified (see a, b, c, and d). For each connection, the test voltage from the
megohmmeter shall be continuously applied to the specimen for a period of 1 minute, +25 percent, -0 percent,
immediately following which the resistance reading of the megohmmeter shall be noted. Care shall be taken during
each such measurement to assure that any electrical jumper leads connecting the specimen to the megohmmeter
shall be spaced sufficiently far from each other and from any common conducting surface that measurement
accuracy shall not be impaired.
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