Abstract: Assessment accuracy of the corona resistance of enameled wires remains a key industry challenge. This study examines the influence of service duration of steel ball electrodes used in corona resistance tester on enameled wire specimens. Results reveal that failure time of enameled wires increases with the extending of the service period of steel ball electrodes regardless of median value or average value. electrodes used less than three months yield time-to-failure data with dispersion comparable to initial data obtained by using new steel ball. And both data groups show no statistically significant difference in mean values. However, failure time data exhibits markedly increased dispersion even includes an extreme abnormal value when the steel ball was used over six months. Statistical analysis confirms a significant difference in mean values between three month and six month datasets while showing no significant difference in median values.