DOI: https://doi.org/10.33994/kndise.2022.67.41

O. Koshel

The article reviews an expert study of conductors with melting due to a short circuit from the places of fires. Given the urgency of the problem of low-quality conductors on sale, the issue of studying such objects is considered. The use of counterfeit cable and wire products leads to fires, resulting in both material losses and deaths, while the number of fires caused by low-quality products is increasing.

For the most used copper wires, the electrical properties are determined by the presence of impurities, some of which have a significant effect on electrical resistance. The technical standards for round copper electrical rolling (rolled wire) regulate 19 types of impurities, the content of which is limited to thousandths of a percentage only. Thus, the oxygen content is limited to 0.04 %.

In counterfeit products the content of impurities can be limited only by the limit of solubility in liquid metal. In particular, the oxygen content can reach such limits when there will be a copper eutectic with an oxygen content of 0.39 %. In this case not only electrical, but also mechanical and external properties will change, which practically are manifested as a decrease in plasticity and defects in the conductor surface.

The development of methods for studying conductors with melting has been going on for more than a decade, but nowadays not all of the issues of methodological support have been resolved. The use of such indicators as presence of an eutectic phase in copper conductors in the case of counterfeit products does not have methodological support and additional research is necessary.

Given the possibility that low-quality conductors could be present among the objects of study, it is proposed to use the results of metallographic studies only for cases of undoubted use of only high-quality conductors.

For express assessment in expert studies of the copper wire quality, it is recommended to use tests for twisting-untwisting (assessment of mechanical properties) and surface evaluation of the conductor under insulation on samples of areas which are not damaged by fire. The parameters of the surface condition and rejection signs, the number of twisting-unwinding cycles are set by the manufacturer depending on the diameter of the wire.

Key words: research of conductors with signs of short circuit, counterfeit conductors, metallographic researches of conductors from fire places.