Inrush Current is caused at the moment the switch is thrown because the filter capacitor acts as a short and the minimum Equivalent Series Resistance of capacitor and line resistance is only a few milli Ohms, leading to a high Inrush Current. Four factors play an important role: Energy of Inrush Current, Minimum Resistance Required by NTC Thermistor (at t=0), Steady State Current, and Ambient Temperature.