Critical overload ignition of XLPE-insulated low-voltage wires: thresholds, fire kinetics and STA-FTIR-based mechanistic interpretation

With increasing end-use electrification, low-voltage distribution wires are subjected to higher overload currents and greater fire risk; however, the ignition thresholds and combustion responses of XLPE-insulated wires remain insufficiently quantified. A 2.5 mm 2 copper-core XLPE wire was tested under steady overload currents of 100–240 A to reproduce self-ignition without an external ignition source, and STA-FTIR was used to characterize the oxidative pyrolysis of the pristine insulation in air. Self-ignition occurred at a critical current of 140 A. Smoke-onset time decreased approximately linearly with current, whereas ignition time followed an exponential decay. The flaming duration showed a non-monotonic trend, peaking at 27 s at 180 A and then shortening at higher currents as earlier fusing reduced the effective fuel-supply window. Maximum flame height and axial spread distance increased with current, with the strongest unsteady fluctuations at 200–220 A and a spread plateau of 75–80 cm above 210 A. STA-FTIR indicates pyrolysis onset near 450 K and a main decomposition peak at 700–750 K, releasing mainly light (partly unsaturated) hydrocarbons together with CO 2 , H 2 O and minor C–O-bearing volatiles. Combining both datasets, a Joule-heating–pyrolysis–near-surface accumulation/auto-ignition framework is proposed to support overload fire-threshold identification and early-warning parameterization. • Critical ignition current of XLPE-insulated wires under overload is identified. • Overload current controls ignition delay and flame spread kinetics. • Joule heating–driven pyrolysis governs source-free ignition behavior.