FED-STD-228A
Method 1331.1
18 April 2014
THICKNESS, SHEATH
1. SCOPE
1.1 This method is intended for use in determining the thickness of rubber and plastic sheaths of
insulated wire and cable.
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 sheath has been removed.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents shall be as follows:
3.1.1 Micrometer caliper graduated to read in mils or 0.0001 inch and having flat surfaces on both the
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.
3.1.2 Wiping cloth.
3.1.3 Alcohol or other suitable solvent.
4. PROCEDURE
4.1 The specimen shall be free from mechanical damage. Any dirt, grease, 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 sheath so that the specimen can just be moved between the anvil and
spindle without distortion of the sheath. The diameter over the sheath shall be read from the micrometer
scale and the value recorded as D1.
4.2 The sheath shall then be removed from the specimen and the diameter over the core (assembly
under the sheath) measured in the same manner as described for diameter over the sheath and the value
recorded as D2.
4.3 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 diameter at the place measured. The
diameter over the sheath and over the core shall be determined as nearly as practicable at the same
point.
5. RESULTS
5.1 Calculation. The thickness of the sheath at any point shall be calculated as follows:
Thickness, inch=D1-D2
2
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