The low-voltage power supply and distribution system is directly linked to the user, characterized by an intricate configuration and inadequate upkeep and repair. This location poses a significant risk for electrical fires. The low-voltage AC series fault arc exhibits negative resistance properties, making it challenging to identify using conventional relay protection systems. Moreover, its elevated temperature can rapidly lead to fire hazards. Therefore, this paper analyzes the physical characteristics of AC fault arc; the magnetohydrodynamics simulation model is constructed to study the temperature change and influencing factors in the stable stage of the arc, and the harm of arc fault is analyzed in combination with the standard. Finally, the experimental platform of AC arc fault ignition risk is built to verify the reliability of the simulation model and show the harm of minor current arc faults. The research uncovers the significant risk and mechanism of ignition caused by fault arcs. It elucidates the progression of the temperature field and clarifies how factors such as current level and arc gap distance influence the arc temperature. Additionally, it identifies the deficiencies in current detection standards and proposes measures for improvement. This research holds great importance in safeguarding against low-voltage series fault arcs.