Sustained overload preconditioning of electrical wires causes Joule-heat accumulation and insulation thermal ageing, which can reshape ignition and combustion development under external radiative heating. To quantify the coupled effects of overload thermal history and incident heat flux on flame-retardant XLPO-insulated copper wires, the specimens were preconditioned at 0 A, 60 A, and 80 A, and then tested in a cone calorimeter under 25–55 kW·m -2 . Time to ignition (TTI), heat release rate (HRR/pHRR), fire performance and growth indices (FPI/FGI), O 2 /CO 2 evolution, and residue morphology were obtained. Increasing heat flux markedly shortened TTI and elevated pHRR and early-stage growth intensity. At 50–55 kW·m -2 , HRR shifted from a single peak to a distinct double-peak pattern, accompanied by stage-dependent O 2 /CO 2 variations. Compared with non-overloaded samples, overload thermal history generally delayed ignition and constrained combustion development. Under the cone calorimeter conditions used in this study, the 80 A preconditioned specimens showed the lowest pHRR, FGI, CO 2 peak values, and comprehensive index H, indicating a suppressed combustion response. A multi-parameter normalized comprehensive index H was proposed using TTI, pHRR, FGI, and CO 2 peak values. H increased monotonically with heat flux and generally ranked 0 A > 60 A > 80 A, enabling comparable characterization of early-stage fire hazard under different conditions. It should be emphasized that this result is limited to the combustion response of overload-preconditioned specimens under cone calorimeter testing and does not imply improved electrical safety or service reliability after overload.
Deng et al. (Mon,) studied this question.