Class 105 paper-covered bare square copper wire typically consists of a square copper conductor covered with a layer of insulating paper.
Insulating Material:
The insulating material shall be rope paper, kraft paper, or both. The paper covering shall be one or more tape layers wrapped firmly, closely, evenly, and continuously around the wire.
Thermal Class: 105 impregnated or in oil. The thermal class of fibrous-covered or paper tape–wrapped wire shall be based on experience.
Dimensions:
The increase in dimensions for coverings having other layers or other tape thickness shall be in accordance with the table.
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 |
Square Wire:
Dimensions of Square Bare Wire
| AWG | Minimum | Nominal | Maximum | Nominal Corner Radius ±25% |
| 1/0 | 8.171 | 8.252 | 8.334 | 1.00 |
| 1 | 7.275 | 7.348 | 7.422 | 1.00 |
| 2 | 6.477 | 6.543 | 6.609 | 1.00 |
| 3 | 5.768 | 5.827 | 5.885 | 1.00 |
| 4 | 5.138 | 5.189 | 5.240 | 1.00 |
| 5 | 4.575 | 4.620 | 4.666 | 1.00 |
| 6 | 4.074 | 4.115 | 4.155 | 0.80 |
| 7 | 3.630 | 3.665 | 3.701 | 0.80 |
| 8 | 3.231 | 3.264 | 3.297 | 0.80 |
| 9 | 2.878 | 2.906 | 2.934 | 0.67 |
| 10 | 2.563 | 2.588 | 2.614 | 0.67 |
| 11 | 2.278 | 2.304 | 2.329 | 0.50 |
| 12 | 2.027 | 2.052 | 2.078 | 0.50 |
| 13 | 1.803 | 1.829 | 1.854 | 0.40 |
| 14 | 1.603 | 1.628 | 1.654 | 0.40 |
Elongation: Not less than 32% for a conductor thickness of 0.049 in. (1.25 mm) and greater, or 30% for a conductor thickness less than 0.049 in. (1.25 mm)
Adherence And Flexibility: Covering shall not loosen appreciably nor open sufficiently to expose the bare wire after bending around a mandrel having a dimension six times the thickness of the bare wire.
Springback: Not greater than 5.5º
This type of wire is commonly used in transformers, motors, and other electromagnetic devices where high temperature resistance and electrical insulation are required.