In presenting this paper to the Institute I wish it to be clearly understood that no attempt has been made to say anything or do anything that would be discourteous to the manufacturers of rubber-covered wire. The main object of the paper is to compare a large variety of rubber-covered wires, especially with reference to power-factor and dielectric loss. So far as I know these tests have not been applied commercially to any extent here. A careful examination of the results given in the paper

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... l show that power-factor tests are valuable in helping to determine the quality of rubber-covered wires, but that they cannot be relied upon to indicate the amount of fine Para. All the tests given are essential, especially the chemical, voltage, and insulation resistance tests. Chas. P. Steinmetz: This paper is interesting in giving what may lead to an advance in our method of judging cables. It proposes to investigate the character of cables by measuring the energy loss in the cable as represented by the power-factor. The energy loss in the cable appears to me a very important quantity. However, I do not believe it would be safe to judge cables merely by this energy loss. What is important in a cable or any condenser is 1: the disrupted strength; that is, that the cable stands the operating voltage with a sufficiently high limit of safety, and 2: the deterioration, that the cable does not deteriorate at the operating voltage wi.thin a reasonable time. Deterioration is the effect of energy consumed in the dielectric of the cable, Therefore, if one could imagine a cable which has no energy loss whatever in the dielectric or zero power-factor, such cable would not deteriorate. This shows the importance of the energy loss in the cable. However, the deterioration is not necessarily, and probably in general is not proportional to this energy loss. We do not know much, to tell the truth, of this energy loss in the dielectric in the alternating field. We suppose there is some kind of a dielectric inolecular friction similar to the molecular magnetic friction of iron; that is, a conversion of electric energy into heat during cyclic changes of static stress. This dielectric hysteresis is harmless, regarding deterioration, because it is a conversion of the energy into heat and merely raises the temperature of the cable slightly, just as the current existing in a conductor raises it, and, if we keep the temperature of the cable sufficiently low, no deterioration will take place owing to this heat. So the production of this additional heat by dielectric hysteresis, must be taken in consideration in designing a cable system.