An evaluation of the accuracy and reliability of enameled wire tests

The recent large increase in the number of new wire enamels, with the attendant emphasis on improvement in some particular wire property, necessitates refocusing our attention on the test methods used to obtain these values. Many of these are time honored tests and it is sometimes taken for granted that they will give meaningful values. This results in a tendency to put a number, or a small range, on a given wire property without any direct reference to the degree of accuracy or reproducibility of the test involved. Further the weighting placed, on the reliability of the test method will vary depending on whether the reader´s viewpoint is in terms of: a. enamel acceptance b. wire mill production c. equipment manufacture. In this paper, an attempt has been made to measure the reproducibility of the tests under carefully controlled conditions, in which the known variables are held constant or deliberately varied in a known manner. Thus, the test variations reported represent the best values to be expected from a given procedure and any change would tend to increase the variation. The large potential variable represented by the cleanliness and condition of the bare wire surface is not treated here. However, several different types of enamel, from different sources, and using different wire samples of each have been used in an attempt to minimize the effect of this variable. Copper wire was used throughout, bare wire diameter ranging from .0253 to .0508 inches. Also, since conceive and smoothness a re properties that will vary continuously over any wire sample, the above procedure will tend to "average out" these variations.