Abstract: With the continuous development of urban distribution networks, loop closure operation becomes an important load transfer method without power interruption to improve grid operation efficiency and service quality. Based on an actual fault case, this paper reconstructs a loop-closure tripping event on a cable-overhead hybrid line in a power supply area. The analysis reveals that the core cause is the superposition of reversed primary cable phase sequence, internal wiring errors in the live-line indicator, and misjudgment of phase verification results. This paper proposes an intelligent live-line indicator with dual functions of external phase verification and internal self-checking. By collecting branch voltages, calculating phase differences in real time, and providing visual alarms, the device accurately determines phase sequence consistency. It reduces the risk of loop closure failure and even remote relay protection tripping caused by secondary equipment wiring errors to the greatest extent. The proposed method provides theoretical support and technical assurance for reliable loop closure operation in distribution networks.