FED-STD-228A
Method 1521.1
18 APRIL 2014
LAY OF TWIST, CABLE
1. SCOPE
1.1 This method is intended for use in determining the lay of twist (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) in terms of the diameter of the finished individual conductors or the pitch
diameter. Pitch diameter of any layer of conductors of a cable is the diameter of the circle passing
through their centers.
2. SPECIMEN
2.1 The specimen should be a piece of the inspection unit of sufficient length to include at least two
complete spirals of the conductors from which any covering over the finished conductors has been
removed.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents shall be as follows:
3.1.1 Steel scale graduated to 1/32 inch or finer or its decimal equivalent.
3.1.2 Wiping cloth.
3.1.3 Alcohol or other suitable solvent.
4. PROCEDURE
4.1 Individual conductor method. The specimen shall be free from mechanical damage. Any fibers,
saturants, or other materials shall be removed from the finished individual conductors by means of the
cloth and solvent. The distance parallel to the axis of the cable in which the conductor makes one
complete spiral shall be measured with the graduated scale to the nearest 1/32 inch and the value
recorded as L. The diameter of the same individual conductor shall be determined as described in
method 1431 and the value recorded as D.
4.2 Pitch diameter method (cable with five or more conductors).
4.2.1 The specimen shall be free from mechanical damage and shall be prepared as described in 4.1.
4.2.2 The distance parallel to the axis of the cable in which the conductors make one complete spiral
shall be measured as described in 4.1 and the value recorded as L1.
4.2.3 The diameter over any layer of conductors shall be measured as described in method 1431 for
diameter over the conductor and the value recorded as D1.
4.2.4 The conductors shall be separated and the diameter of a single finished conductor of the same
layer measured as described for diameter over the layer and the value recorded as D2.
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