FED-STD-228A
Method 1431.1
18 APRIL 2014
SIZE, CONDUCTOR
1. SCOPE
1.1 This method is intended for use in determining the size of solid and stranded conductors of insulated
wire and cable. For the purpose of this method, the term "wire" should be defined as a slender rod or
filament of drawn metal.
2. SPECIMEN
2.1 The specimen should be the bare conductors removed from a piece of the inspection unit at least 6
inches in length.
3. APPARATUS
3.1 The apparatus shall consist of a micrometer caliper graduated to read in 0.1 mil or 0.0001 inch and
having flat surfaces on both anvil and end of spindle, each approximately 0.25 inch in diameter. The
surfaces of anvil and spindle shall be parallel to within 0.0001 inch.
4. PROCEDURE
4.1 Solid conductors. The specimen shall be free from mechanical damage. The micrometer caliper
shall be applied directly over the conductor so that the anvil and spindle are just brought into contact with
the specimen in such a manner that the conductor is not distorted. The criterion of contact is the initial
development of frictional resistance to movement of the specimen between the micrometer surfaces. The
diameter of the conductor shall be read from the micrometer caliper scale and the values recorded. Two
measurements of the diameter at positions approximately 90° apart on the specimen shall be made.
4.2 Stranded conductors. Individual wires of a stranded conductor cable shall be measured separately
as described for solid conductors in 4.1. Unless otherwise specified in the detail specification, 10 percent
of the wires and in no case less than seven wires shall be taken from the conductor for test. Wires shall
be selected at random from each layer of the conductor and the number selected from each layer shall be
proportional to the number of wires in the layer.
4.3 If tin or other metal coatings are present, the diameter measurements shall be made over the
coating.
5. RESULTS
5.1 Calculation.
5.1.1 Solid conductor. The size of the conductor at any point, in circular mils, shall be calculated by
squaring the diameter expressed in mils.
5.1.2 Stranded conductors. The size of the stranded conductor in circular mils shall be calculated as
follows:
2
2
2
Size of wire, circular mil=D1 +D2 +- - - - - - -+Dn
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