Abstract: A simulation was conducted to study the heating process and the melted mark formation of the ZR-BV single-core copper wire under overcurrent. The formation process was shot by a high-speed camera and analyzed frame by frame. The result shows that,when overcurrent fault occurs, when I≤3.5Ie, overcurrent conductors only have the phenomenon of core heating and insulation pyrolysis damage; When I≥4Ie, the overcurrent wire will ignite the insulation.There are two kinds of insulation combustion: When I<4.5Ie, the fire of the insulation burning can spread only from the breaking point to a certain point on both sides of the conductor; When I≥4.5Ie, the fire of the insulation burning can spread to the end of the wire from the breaking point on both sides and it is this insulation combustion that causes the formation of globules. Dendritic crystal structure is the typical structure of globules. This study shows that there will be flame when energized conductor carries large current. 

Key words: fire investigation, electrical fire, copper wire, overcurrent, heating process, globules