Accurate, economical, and reliable detection of series arc faults is one of the key approaches to preventing electrical fires. To address the challenges in single-ended series arc detection in low-voltage AC distribution systems, specifically, the difficulty in identifying the fault location and extracting transient components, a boundary-active series arc fault detection method is proposed, which can isolate the fault zone while reducing the complexity of fault feature extraction. First, the characteristics of the high-frequency components generated by series arc faults are analyzed, revealing that relying solely on the natural attenuation of the line cannot ensure absolute selectivity in fault identification. Then, the influence of ferrite magnetic ring boundary on the high-frequency characteristics of series arc faults is analyzed. Finally, based on the characteristics introduced by the added magnetic ring boundary, a detection method is developed that identifies series arc faults by analyzing the differential voltage of adjacent waves on both sides of the magnetic boundary. It is found that the proposed boundary element can significantly attenuate the propagation of high-frequency components, effectively isolating the fault zone’s high-frequency signals. Moreover, the boundary-based high-frequency voltage detection method eliminates the need for high-precision current sensors. Experimental results show that the proposed method can effectively avoid the interference from external faults and achieve reliable detection of series arc faults in low-voltage distribution systems.