FED-STD-228A
Method 1011.1
18 April 2014
THICKNESS, INSULATION; MICROMETER CALIPER
1. SCOPE
1.1 This method is intended for use in determining the thickness of the insulation of insulated wire and
cable. It is not recommended for use when the thickness of the insulation is less than 3/64 inch.
2. SPECIMEN
2.1 The specimen should be a piece of the inspection unit at least 2 feet in length from which any
covering over the insulation has been removed.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents should be as follows:
3.1.1 Micrometer caliper graduated to read in mils of 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 should
be parallel to within 0.0001 inch.
3.1.2 Wiping cloth.
3.1.3 Alcohol or other suitable solvent.
4. PROCEDURE
4.1 Average thickness.
4.1.1 The specimen shall be free from mechanical damage. Any saturants or other extraneous materials
shall be removed from the specimen by means of the cloth and solvent. The micrometer caliper shall be
applied directly over the insulation so that the specimen can just be moved between the anvil and the
spindle without distortion of the insulation. The diameter over the insulation shall be read from the
micrometer caliper scale and the value recorded as D1.
4.1.2 The insulation shall then be removed from the conductor and the diameter over the conductor or
the separator (if one is used) measured as described above and the value recorded as D2. If a separator
is present, the diameter over the separator shall be measured as described for the diameter over the
insulation. If a separator is not present, the anvil and spindle of the caliper shall just be brought into
contact with the surface of the conductor 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 conductor
between the micrometer surfaces.
4.1.3 Three sets of measurements equally spaced along the length of the specimen shall be made.
Each set of measurements shall consist of the maximum and minimum diameters at the place measured.
The diameter over the insulation and over the conductor or separator (if one is used) shall be determined
as nearly as practicable at the same point.
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