A study of Time/Current Characteristics of the Ignition Processes in Cellulosic Material Caused by Electrical Arcing for Application in 240V Arc-Fault Circuit Interrupters

Abstract

In the development of Arc-Fault Circuit interrupters (AFCIs), one of the most important parameters is the time that an arcing fault could persist before the device will interrupt the current flow and hopefully mitigate fire propagation. In 1996 Underwriters laboratories (UL) published a report on time/current ignition characteristics of arcs at 120 V. Despite the very limited number of tests (195), the obtained data still are used to develop trip times for 120 V rated AFCIs. Continuous expansion of AFCI applications from the dwelling unit bedrooms to other living areas requires knowledge of ignition characteristics at 240 V in order to specify times necessary to clear arcing faults with 240 V AFCIs. This work presents results of research on ignition characteristics of cotton fire indicators caused by electrical arcs with currents ranging from 2 A to 45 A and times from 10 s to 20 ms, when supplied by a 240 V circuit. The total number of tests exceeded 6,000 and provides a statistically acceptable confidence level. The paper examines the role of statistical analysis with respect to the ignition phenomenon due to random variations in the formation of a carbonized path. The duration of actual arcing time is compared with ignition yielding different forms of combustion. The experiments revealed that ignition is possible at currents as low as 2 A. This paper also analyzes the role of temperature rating of PVC wire insulation and other related parameters. Findings could be useful for the future development of 240 V AFCIs.