Arc Bead
Definition
A small, rounded, resolidified deposit of copper or aluminium formed when an electrical arc melts the conductor and the material rapidly re-solidifies; distinguished from fire-induced melt globules by SEM/EDS microstructural analysis.
- Material
- Copper or aluminium conductor
- Formation
- Electrical arc melts conductor, rapid resolidification
- Distinguishing method
- SEM/EDS microstructural analysis
- Confused with
- Fire-induced melt globules
Common questions
Why is it important to distinguish an arc bead from a fire-melt globule?+
An arc bead indicates the wire was energized and arcing at the moment of melting, which can point to an electrical ignition source, while a fire-melt globule forms when external heat simply melts the conductor after the fire started, so misreading one as the other can wrongly identify or exclude an ignition cause.
What does SEM/EDS analysis actually detect to make this distinction?+
It reveals the internal grain structure, voiding pattern, and elemental composition of the melted region: arc beads typically show a distinct crystalline resolidification pattern and characteristic voids from rapid cooling that differ from the microstructure produced by slower external heating.
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