An Analysis of Thermally Induced Arcing Failure of Electrical Cable

Abstract

Arc failure of Southwire Romex Simpull non-metallic sheathed 14/2 American wire gauge (AWG) with ground cable due to external heat was examined. This type of cable was selected due to its widespread use in residential building wiring. This research is motivated by the fact that currently there are no widely accepted methods or models used to predict electric arc failure in cables exposed to thermal conditions or to determine whether an arc failure event was the cause or result of a fire. A variety of tests were performed at various temperatures to learn more about the arc failure of these cables. The cables were exposed to precise temperatures with a steady heating rate in a convection oven in order to best attempt to eliminate heat transfer through the cable. In order to explore the effect current may have on the time to arc failure of the cable, experiments at different temperatures were performed in both loaded and unloaded scenarios. During many of these tests, voltage and current measurements were collected during an arcing event. As part of the process of exploring the events leading up to arc failure, electrical resistance tests of the cable's insulation components were examined. A model was developed to predict time to arc failure at a variety of temperatures based on thermal degradation of the PVC insulation. The purpose of the developed model is to be able to predict cable failure based on known thermal conditions. The proposed values of the model developed are in examining a prior thermally induced electrical arcing incident or in determining the suitability of a cable in an abnormal thermal environment. The results of this research will be useful in continuing the research and education of the arc failure of electrical cables.