DISTINGUISHING BETWEEN ARCING AND MELTING\u00a0DAMAGE IN ELECTRICAL RECEPTACLES<\/p>\n
Matthew Benfer and Daniel Gottuk
\nHughes Associates Inc., USA<\/p>\n
Presented at\u00a0International Symposium on Fire Investigation<\/a>, 2014<\/p>\n ABSTRACT<\/p>\n The majority of fire-investigation related literature on electrical arcing focuses on copper wiring, both stranded and\u00a0solid, with some attention paid to steel (i.e., conduit), and relatively little mention of brass. This is despite the\u00a0relatively equal presence of copper, steel, and brass in receptacles and similar electrical devices. Changes to NFPA\u00a0921 in the 2014 edition of the guide expand upon the characteristic traits which can be used to assess whether arcing\u00a0or melting is present in a conductor. However, most of the characteristic traits of arcing and melting are qualitative\u00a0and not well defined in NFPA 921, which leads to more subjective evaluations. In addition, a myopic examination of\u00a0evidence with respect to the presence of one or two characteristic traits can lead to a false indication of arcing. In\u00a0cases such as this, other evidence of melting (i.e., in close proximity to the area in question) could preclude\u00a0confirmation of arcing.<\/p>\n The purpose of this work was to determine which characteristic traits are effective in assessing potential arcing\u00a0damage on receptacle components and wiring. A total of 86 receptacles were evaluated in this study. Thirty-nine\u00a0receptacles failed as a result of an overheating connection resulting in arcing damage; this included 95 individual\u00a0conductors. Forty-seven receptacles with fire-induced arcing were also evaluated; this included 87 individual\u00a0conductors. All of the evaluated receptacles with fire-induced arcing were energized or energized with a load during\u00a0testing. In contrast, thirty-seven non-energized receptacles with fire induced melting were evaluated with 57\u00a0individual conductors.<\/p>\n The characteristic arcing traits which were evaluated include: corresponding damage on the opposing conductor;\u00a0localized point of contact with a sharp line of demarcation between undamaged and damaged areas; round, smooth\u00a0shape; resolidification waves; tooling marks visible outside the area of damage; internal porosity; spatter deposits;\u00a0and small beads and divots over a limited area. The characteristic traits of melting which were evaluated include:\u00a0visible effects of gravity; gradual necking of the conductor; and pitting, thinning, and presence of holes in the\u00a0conductor. These traits were taken from the literature (e.g., NFPA 921) and from observations made during the\u00a0forensic examinations of receptacles and wiring conducted as part of this work. For each characteristic, there were\u00a0three possible outcomes: Yes, No, and Possible. Yes indicated that the characteristic was judged to be present on the\u00a0particular conductor; no indicated that the characteristic was judged not to be present on the conductor. Possible\u00a0indicated that confirmation could not be made either for or against the presence of the characteristic. All of the\u00a0evaluations were conducted by the same person.<\/p>\n Corresponding damage on the opposing conductor, localized damage with a sharp line of demarcation, and tooling\u00a0marks outside of the area of damage were observed on significant portions of arc damaged conductors and small\u00a0numbers of conductors with melting damage; these characteristics were found to be strong indicators of arcing.<\/p>\n Using multiple characteristic traits and contextual information for determination of arcing vs. fire-melting provides\u00a0greater confidence in the evaluation of damage. In addition, visual examinations were found to be reliable indicators\u00a0of both arcing and fire-melting for most conductors. However, there are some cases which would benefit from more\u00a0advanced examination techniques including SEM\/EDS examinations, X-ray, CT scanning (X-ray computed\u00a0tomography), cross-sectioning and polishing, or other metallurgical methods.<\/p>\n Download the complete paper<\/a> here.<\/p>\n","protected":false},"excerpt":{"rendered":" DISTINGUISHING BETWEEN ARCING AND MELTING\u00a0DAMAGE IN ELECTRICAL RECEPTACLES Matthew Benfer and Daniel Gottuk Hughes Associates Inc., USA Presented at\u00a0International Symposium on Fire Investigation, 2014 ABSTRACT The majority of fire-investigation related literature on electrical arcing focuses on copper wiring, both stranded and\u00a0solid, with some attention paid to steel (i.e., conduit), and relatively little mention of brass. … Continue reading Distinguishing Between Arcing and Melting Damage<\/span>