The effects of wire diameter and thermal conductivity of core materials on downward flame spread were investigated through measurements of the limiting oxygen concentration (LOC) and flame spread rate. Low-density polyethylene (LDPE)-insulated copper (Cu) and nichrome (NiCr) wires were used as test specimens, with three different wire diameters prepared to examine the influence of wire geometry on flammability. For Cu wires, the LOC increased with increasing wire diameter, indicating reduced flammability. In contrast, for NiCr wires, the LOC decreased as the wire diameter increased, suggesting enhanced flammability. Based on the experimental results of flame spread rates for each specimen, the heat transfer within the insulation and core and the flammability limit of the insulation material were examined.
KUBOTA et al. (Wed,) studied this question.