On physical basis of local current overload in vehicle electric mains

Introduction. The data presented in the article indicate that the problem of improving fire safety of vehicles is very topical. The aim of the article is to develop a scientifically based method for studying a copper conductor with signs of local current overload in order to establish the cause of its damage during a fire-technical examination. Materials and methods. The studies were carried out with a JSM-6390LV scanning electron microscope with an add-on device for energy dispersive microanalysis. The fracture surfaces of the copper conductor were ana¬lyzed without preliminary sample preparation. Theoretical foundations (theory and calculations). An updated model of ultimate stress-strain state of inelastic pure bending of a copper rod of circular cross section has been developed. The solution has been reduced to simple rating formulas that allow us to evaluate the bearing capacity of flexible single copper conductors. The applicability of the developed mathematical model during the fire-technical examination is shown by a specific example. Results and discussion. Examples of vehicle fires caused by critical bending of the wiring harness are given in the article. Experimental data confirmed that the copper conductor under current overload melts in the critical bend area. The need to clarify the wording of the term “local current overload” is justified. Conclusion. A method for determining the critical bending of a copper conductor at which its melting can occur -under electric current has been proposed. The data presented in the article can be used by experts in an expert study of copper conductors from fire sites to establish the mechanism of their damage and, ultimately, the cause of a vehicle fire.