Reconstruction and fire risk assessment of arc‐tracking at a plug‐outlet connection point

Abstract

Polyvinyl chloride (PVC), a typical plug insulating material, is an organic material with high tracking resistance. However, the tracking resistance of PVC gets considerably reduced by thermal degradation. In this study, a phenol resin with low tracking resistance was implanted between plug blades as an insulating material that simulated the thermally degraded insulating material of the plug, and a method that could efficiently and reliably reconstruct the arc-tracking was proposed. Also, arc-tracking experiments using the proposed method were conducted to evaluate fire risk at the plug-outlet connection caused by arc-tracking. To reconstruct the end state of insulation failure in which the tracking resistance of the plug insulation material deteriorated due to thermal degradation, the insulation material between the blades of a 12 A, 125 V rated PVC plug was cut out. Then, a phenol resin piece (6 or 3 mm width) was implanted in the entire, upper or lower halves between the plug blades.The end state of insulation failure was accelerated by applying carbon grease to the phenol resin surface. The implanted plug was inserted into a 15 A, 125 V rated outlet connected to a 100 V AC commercial power supply, and the arc-tracking at the plugoutlet connection was observed. When the width of the phenol resin to be implanted was 3 mm, we found that the outlet plate and plug could ignite due to the longer electrical discharge duration. The plug was often extinguished immediately after the end of the electrical discharge due to the self-extinguishing properties of PVC, but when an acrylonitrile butadiene styrene resin outlet plate ignited, the combustion continued for several minutes. Even though PVCs have self-extinguishing properties, they burn temporarily during arc-tracking. From the results, the flame from the electric fire outbreak is believed to spread to the outlet plate and eventually developed into a fire.