Effectiveness of Circuit Breakers in Mitigating Parallel Arcing Faults in the Home Run

NOTICE The issuance of this Report does not constitute an endorsement of any proposed amendment and in no way implies Listing, Classification, or other recognition by UL and does not authorize the use of UL Listing or Classification Marks or any other reference to Underwriters Laboratories Inc. on, or in connection with, the product. Underwriters Laboratories Inc., its employees, and its agents shall not be responsible to anyone for the use or nonuse of the information contained in this Report, and shall not incur any obligation or liability for damages, including consequential damages, arising out of or in connection with the use of, or inability to use, the information contained in this Report. Electrical wiring in the home can get damaged during installation or afterwards, through over-stapling, crushing, bending, penetration by screws and nails, and through rodent and insect damage. Over time cabling may degrade further due to exposure to elevated temperatures or humidity, eventually leading to arcing faults and ignition of combustibles in proximity. The length of electrical wiring between the circuit breaker panel and the first receptacle is often referred to as the " home-run ". To protect the wiring from damage and subsequent potential for arcing, the National Electrical Code (NEC ®) requires protection of the home run wiring using conduit or armored cabling 1 if a receptacle-mounted AFCI (known as Outlet Branch Circuit Arc-Fault Circuit-Interrupter, or OBC AFCI, in the NEC) is used in a residential circuit. This requirement was put in place since such an arc protection device would not be able to provide parallel arcing fault protection for the home run, i.e., de-energize the circuit, if the fault is upstream of the OBC AFCI. In this situation, the circuit breaker is the only means for mitigating the fault, though it is intended for protecting the wiring from overheating due to an overcurrent condition and is not intended for mitigating arcing faults. Since parallel arcing faults may deliver relatively high currents, there is the possibility that it may trip the circuit breaker and de-energize the electrical circuit. However, the ability of a circuit breaker to mitigate a parallel fault condition has not yet been well characterized in the available literature. Thus, experimental data was required to determine whether a circuit breaker may mitigate a parallel arc fault, and more specifically, the conditions under which effective protection is attained. This research work was conducted using commercially …