Application of Insulation
Wire shall be coated or covered with insulation that meets the applicable requirements when the wire is taken directly from the spool, reel, or container.
Essentially, film coatings shall be smooth and continuous, free from streakiness, blisters, and foreign material, in accordance with good commercial practice.
When the wire is both film-coated and fibrous- or tape-covered, the film-coated wire shall meet the applicable requirements of before it is covered.
Fibrous coverings shall be wrapped firmly, closely, evenly, and continuously around the wire. When more than one tape covering is applied, adjacent tapes shall be permitted to be wound in the same or in opposite directions. The relation of the percentage of overlap of the tape to the number of layers of tape is shown as follows:
| Wrap Description | Number of Tape Layers (N) |
| Percentage of Overlap | |
| 0 | n |
| Greater than 0 to 25 | 1.33n |
| Greater than 25 to 33 | 1.5n |
| Greater than 33 to 40 | 1.67n |
| Greater than 40 to 50 | 2n |
| Greater than 50 to 67 | 3n |
| Greater than 67 to 75 | 4n |
The increase in diameter due to the tape covering for round tape-covered wire, and the increase in thickness due to the tape covering for rectangular and square wire shall be in accordance with NEMA MW 100 Table 21, 22, or 23, as indicated in Part 2, and are determined as follows:
Minimum thickness or diameter increase = 2(0.85)Nt
Maximum thickness or diameter increase = 2(N+1)t, (see note 1 below)
Where:
N: Quantity of layers n: Quantity of tapes
t: tape thickness (nominal)
The increase in width of square and rectangular wire due to the tape covering shall be equal to or less than the increase in thickness.
NOTE 1—The calculated maximum increase due to tape covering may be exceeded provided the measured overall dimension of the covered wire does not exceed the sum of the specified maximum conductor or film insulated thickness or diameter plus maximum increase due to covering.
NOTE 2—Number of tapes or layers, tape thickness, sides of application of fluorinated polymer adhesive, when applicable, and percentage of overlap are agreed on between user and supplier.