MIL-DTL-8777F
4.6.2.3 Conductors, elongation. Elongation tests on the copper strand removed from the finished wire
shall be performed as specified in method 3211 of FED-STD-228.
4.6.3 Primary insulation.
4.6.3.1 Concentricity. The concentricity of the primary insulation shall be determined as specified in
4.6.3.1.1 and 4.6.3.1.2. All wall thickness measurements shall be determined under suitable
magnification.
4.6.3.1.1 Primary insulation (wire sizes 22 through 12). The concentricity of the primary insulation of
wire sizes 22 through 12 shall be determined by first locating and recording the minimum wall thickness of
a cross section of the primary insulation. The maximum wall thickness of this same cross section shall be
measured and recorded. A wall thickness measurement shall be interpreted to be the minimum distance
between the outer rim of the outermost strand of the conductor and the outer rim of the primary insulation.
Percent concentricity is defined as 100 times the ratio of the minimum wall thickness to the maximum wall
thickness.
4.6.3.1.2 Primary insulation (sizes 10 through 00). The concentricity of the primary insulation shall be
determined, on a cross section of the insulation removed from the finished wire, by first locating and
recording the minimum wall thickness of the primary insulation. From this point, on the outer rim of the
primary insulation at which the minimum wall thickness was measured, three more reference points 90
degrees apart on the outer rim of the primary insulation shall be established. At each of these three
reference points, the nearest member of a rope-lay conductor shall be selected and the insulation wall
thickens between that member of the rope-lay conductor and the outer rim of the primary insulation shall
be measured. The average of the four readings shall be considered to be the average wall thickness. A
wall thickness measurement shall be interpreted to be the minimum distance between the outer rim of the
primary insulation and rim of the outermost strand of the stranded member of the rope-lay conductor.
Percent concentricity is defined as 100 times the ratio of the minimum wall thickness to the average wall
thickness.
4.6.3.2 Physical properties of extruded primary insulation.
4.6.3.2.1 Tensile strength and elongation. Physical properties tests of the primary insulation shall be
made on samples removed from the finished wire, and as specified in method 3211 of FED-STD-228.
4.6.3.2.2 Aging.
4.6.3.2.2.1 Air oven (quality conformance test). Specimens of the primary insulation removed from a
finished wire shall be suspended in a gravity-convection type air oven at a temperature of 232° ± 5°C for
6 hours. Following this procedure, the tensile strength and elongation of the specimens shall be
measured within 16 to 48 hours after removal from the air oven and a specified in method 3211 of
4.6.3.2.2.2 Air oven (qualification test). The test specified in 4.6.3.2.2.1 shall be performed as
specified, except that the temperature shall be 200° ± 5°C and the exposure time 200 hours.
4.6.3.2.2.3 Oxidation (qualification test). Specimens similar to those employed in the tensile strength
and elongation test specified in 4.6.3.2.1 shall be placed in an oxygen bomb (Bierer-Davis or equivalent)
and subjected to an oxygen pressure of 300 psi and a temperature of 80° ±3°C for 7 days. Following this
test, the tensile strength and elongation of the specimens shall be measured with 16 to 48 hours after
removal from the oxygen bomb, and as specified in method 3211 of FED-STD-228.
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