Arcing Faults in Metallic Conduit at 120 and 240 V

Over the years, many fires have been blamed on the failure of electric equipment or wiring in residential or commercial installations. To help resolve the question of whether or not these accusations have substance, many tests have been performed to evaluate various types of wire and insulation in different environments on 120- and 240-V ac circuits. Evidence from a recent fire in a local commercial installation at 208/120 V indicated that paper products lying on the exterior of a conduit were ignited due to an internal arc between a conductor and the metallic conduit wall. The fault current did not trip a standard 100-A plastic case panel breaker. Laboratory tests were performed in an attempt to duplicate the conditions and confirm the conclusions. The results are reported.