FED-STD-228A
2.13 Insulation resistance. The insulation resistance of an insulated conductor is the electrical resistance
offered by its insulation to an impressed direct-current potential tending to produce a leakage of current
through the same.
2.14 Lay of twist. The lay of twist is the ratio of the length of lay to the diameter of an individual finished
conductor or to the pitch diameter of any layer of conductors of which the cable is composed.
2.15 Length of lay. The length of lay of any helically wound strand of insulated conductor is the axial
length of one complete turn of the helix, usually expressed in inches.
2.16 Median. When the numerical values for a given property are arranged in ascending or descending
order, the median is obtained as follows:
a. When the number of values is odd, the median is the middle value in the series.
b. When the number of values is even, the median is the arithmetic average of the two middle values.
2.17 Picks per inch. Picks per inch is the number of carriers in either direction contained in 1 inch of the
braid measured parallel to the axis of the finished wire or cable.
2.18 Pitch diameter. The pitch diameter of any layer of conductors of a cable is the diameter of the circle
passing through their centers.
2.19 Ply. A ply is an individual single yarn in a ply yarn.
2.20 Ply yarn. A ply yarn is the product formed by twisting together two or more single yarns.
2.21 Rope lay. In a rope-lay conductor the stranded members are twisted together with a concentric lay,
and the stranded members themselves may have either a bunched, concentric, or rope lay.
2.22 Shielded pair. A shielded pair is a twisted pair over which a close braid of copper wire has been
applied.
2.23 Stranded conductor. A stranded conductor is a conductor composed of more than one wire.
2.24 Tearing strength. Tearing strength is the ratio of the maximum force applied during tear of a
specimen to the thickness of the unstretched specimen.
2.25 Tensile strength. Tensile strength is the maximum force per unit of the original cross-sectional area
of the specimen which results in the rupture of the specimen. It is calculated by dividing the maximum
force in pounds by the original cross-sectional area in square inches.
2.26 Tensile stress. Tensile stress is the force per unit of original cross-sectional area of the unstretched
specimen required to stretch the specimen to a stated elongation. It is expressed in pounds of tension
force per square inch at the stated elongation. For example, 1,000 pounds per square inch at 500
percent elongation. It is often designated in rubber technology by the term "modulus".
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