Effect of the Current on the Fire Characteristics of Overloaded Polyvinyl Chloride Copper Wires

Abstract

In this study, the fire behavior variation of unenergized polyvinyl chloride (PVC) copper wires subjected to overload with different currents was investigated by a cone calorimeter. Overload currents were selected from 1 times safe-rated current (Ie) to 3.5 times Ie to obtain tested sample wires. The mass fraction, time to ignition (TTI), heat release rate (HRR), gas emission, and residue were measured. If the current flowing through the wire increased up to 3.5 times Ie, the TTI of this unenergized wire increased drastically and the peak HRR (pHRR) decreased notably so that the flame growing index (FGI) reduced considerably. When the wire carried less than three times Ie, the FGI remained stable. For all overloaded PVC copper wires, the increase in the heat flux resulted in a higher pHRR and a lower burning duration. However, regardless of the external heat flux exposure, the FGI of copper wires overloaded at 3.5 times Ie was lower than that of copper wires carrying less than other times Ie. Moreover, the consumption of O2 and generation of CO2 as the heat flux varied were consistent with that of the HRR. Opposed to expectation, the flame propagation of unenergized PVC copper wires would decline in a fire, if the wire has been damaged by overload with some currents.

Effects of Overload on Thermal Decomposition Kinetics of Cross-Linked Polyethylene Copper Wires

“…When the wire diameter in an electrical circuit is insufficient or the overcurrent protection device fails, the current passing through the wire surpasses its safe limit, which is referred to as an overload fault in the Guide for Fire and Explosion Investigations (NFPA 921-2021) [2]. Exceeding the safe current limit for a prolonged period of time causes the Joule heat generated by the metal core of the wire to damage the internal structure of the polymer insulation via thermal conduction, thereby altering fire hazard [3,4]. Cross-linked polyethylene (XLPE)-insulated copper wires with good electrical and mechanical properties are widely used in nuclear power plants, hospitals, schools, and residential buildings.…”