Abstract: This paper conducts a comprehensive process study, from remote monitoring and on-site diagnosis to root cause analysis, addressing an abnormal intermittent voltage phenomenon observed at a 10kV high-voltage user within the electricity consumption information collection system. Through the system, it was discovered that one line voltage (Ucb) of the user"s three-phase three-wire energy meter intermittently dropped from the rated 100V, reaching a maximum drop to 40V, while the other line voltage (Uab) remained normal. On-site inspection and insulation testing determined the fault causes to be corrosion of the cartridge contact finger and moisture ingress in the c-phase current transformer due to prolonged exposure to a high-humidity environment. This led to insulation degradation and triggered intermittent partial discharge. This paper analyzes, in conjunction with the energy meter wiring diagram, the reason why moisture-induced discharge in the current transformer caused voltage fluctuations in the meter. Finally, the fault was promptly resolved through equipment replacement and environmental remediation, thereby ensuring normal power supply for the customer. This study provides a reference for addressing similar voltage anomalies in energy meters under high-humidity conditions.