## 7 Conclusions  
We were able to conclude from our study that an arc fault in a copper-based contact is not of the classical spark gap theory where an electrical breakdown happens between a very small gap with a certain atmosphere. The mechanism behind a copper-based low voltage arc fault is largely another state of glowing connection where the semiconducting property of the material creates an illusion of a sparking gap on the affected area. Our study pointed out that common commercial electrical contact surfaces, especially replacement electrical plugs used around the world, are generally made from non-plated copper or electrical grade brass. When the contact surface is subjected to incorrect handling, such as turning on the electrical appliance before turning on the socket, a small electrical discharge will be created that is sufficient to reduce the contact surface area. Repeatedly mishandling the socket can drastically increase the chance of subjecting the contact point to the Joule heating effect. The risk becomes more pronounced when the contact surface is already being used at its maximum current rating. Due to the semiconducting property of copper oxides, once the temperature from the Joule heating effect is high enough to reduce the resistance of the oxides at the contact area. The specific voltage and current waveform pattern of an arc fault exclusive to copper oxides may occur and furthermore increase the temperature, in turn drastically increasing the risk of an electrical fire. The mechanism for this type of arc fault is unique to contact surfaces that are made from copper or copper alloys. Hence, the other type of material's arc fault, such as steel-based contact, cannot be used as a comparison to all types of low-voltage arc fault. It is also concluded that copper-based arc-fault risk is not exclusive to electrical plugs, sockets, and cables. Any electrical device that is made from internal moving contact parts made of copper is a fire hazard risk. At this time, with the proliferation of small electrical devices around household, this type of electrical fire around the world may increase significantly in the upcoming future. Further research may be required to study the electrical behavior of the iron oxides and create the comparison between the other main types of conductors used in households. In conclusion, any conducting surface used in the contact part that is made of copper or alloys of copper bear an inherent risk of electrical fire hazard due to its properties. In the future, if we want to reduce the risk of such an incidence from this type of hazard, all types of contact conductor should be made from non-copper materials, or all the surfaces must be plated with corrosive resistance material. As, currently, nickel-plated copper is mainly used only on the plug blade but not the interior of the electrical socket, silver-plating is used in electrical switches and breakers which may prove to be insufficient in reducing the risk. The explained mechanism can also be used to pinpoint and create the mean to detect the phenomenon more accurately.  
**Author Contributions:** Conceptualization, S.W.; methodology, S.W.; validation, S.W. and K.Y.; formal analysis, S.W.; investigation, S.W.; resources, K.Y.; data curation, S.W.; writing--original draft preparation, S.W.; writing--review and editing, K.Y.; visualization, S.W.; supervision, K.Y.; project administration, K.Y.; funding acquisition, K.Y. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The study was supported by Tokyo Fire Department.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.