Electrical Receptacles - Overheating, Arcing, and Melting

Abstract

This study was designed to experimentally characterize factors that can cause electrical failures (i.e., overheating connections), to assess the damage and potential forensic signatures of these failures, and to characterize the similarities and differences between arcing and melting in receptacle components and wiring. Laboratory testing evaluated the impact of a wide range of variables on the formation of overheating connections in residential duplex receptacles including screw terminal torque, wiring method (back-wired, or side-wired), and primary receptacle materials. A total of 408 trials of receptacles with various terminal connections were tested in the laboratory setting; receptacles were powered for up to 16 months. A small portion of receptacles with loose connections overheated to the point of failure of the receptacle; some including flaming events. Failure events occurred between 5 and 365 days after tests were started. Four hundred and sixty eight (468) receptacles were placed in compartment fire tests and furnace fire tests. These tests were designed to evaluate the persistence after fire exposure of overheating/arcing evidence from failure events (i.e., from potential fire cause events). The fire exposure tests also served to analyze the characteristic traits of arcing and melting damage. The results indicated that only very loose connections (less than 0.339 N-m [3 in-lb]) at moderately high currents (9A or higher) tend to form significant overheating connections and receptacle failures, irrespective of other variables such as receptacle materials and installation. Characteristic indicators of overheating and glowing terminal connections were identified and were found to persist after fire exposure.