Rectangular wire (a) Bend test for film-coated rectangular and square wire

Realizing the demands concerning the winding of coils and shapes which are required to comply with new and more compact designs, the requirements of the old NEMA specifications were reviewed and upgraded in the new NEMA Magnet Wire Standards publication. While the tests for flexibility are adequate for controlling the necessary properties required for round insulated magnet wire, it seemed appropriate that a further study should be initiated regarding the flexibility requirements of square and rectangular shapes. Therefore, the committee set up a program to investigate the problem and, as would be expected, it was confirmed that the failures occurred in the areas of greatest stress. However, it was also determined that these defects were not only on the outer edge of the bend where the film coating is required to meet added stress due to elongation, but also on the inner edge where the film coating is compressed. This presented a new aspect to the problem since there were no tests which could evaluate this occurrence.