Abstract: To thoroughly investigate the impact of conductor length on the ignition, combustion, and fire propagation behavior of overcurrent polyvinyl chloride copper conductors, an electrical fire fault simulation apparatus was utilized to simulate overcurrent faults in copper conductors of varying lengths. The analysis focused on the effects of conductor length on the ignition and combustion processes, as well as the maximum distance of fire spread, with fire spread rate analyzed using video image stacking techniques. The results indicate that, with a constant overcurrent value, the maximum distance of fire spread initially increases and then decreases with an elongation of the conductor length. For the 2.5 mm2 multi-core polyvinyl chloride copper conductors used in the study, at a constant overcurrent value and a conductor length of 240 cm, the maximum fire spread distance is observed, with the flame reaching full-line combustion at 200 A. The fire spread rate is fastest at the moment of conductor melting, spreading rapidly to both sides. As one moves away from the melting point, there is a decreasing trend in the fire spread rate, coinciding with a decline in combustible gas concentration and temperature in the unburned zone, accompanied by significant fluctuations.

Key words: overcurrent fault, polyvinyl chloride copper wire, conductor length, fire spread distance, fire spread rate