Microstructure and component analysis of glowing contacts in electrical fire investigation

Glowing contacts triggered by poor electrical contacts can pose serious fire risks. In this paper, we conduct experiments on glowing contacts, considering the effects of currents and wire diameters. Surface morphology, cross-section metallographic, and chemical composition of the glowing contact oxide bridge are studied using SEM-EDS, metallurgical microscope, and Raman spectrometer. Six typical microstructural properties and three compositional distribution features of glowing contacts are summarized. Dendrites or refined equiaxed grains on the filament region, coarse grains with tiny currents, disappearance of grain boundaries with high current, and leaf-shaped grains near the junction area are all representative features. The microstructure of glowing contacts turns out to be quite different from that of short-circuit-melted marks. Based on copper oxidation theory and solidification theory, we also describe the formation mechanism for the characteristic microstructural features and oxidation products. The patterns can be used to determine the presence of glowing contacts in fire accidents.