Third Factor is the steady state current. Operating current must be at or below the steady state current rating of the NTC Thermistor. Maximum Steady State Current can be found by: Imax=Output Power / Efficiency*Input Voltage where Imax is Maximum Steady State Current, Output Power is Output Power of the Power Supply, Efficiency is Efficiency of Power Supply and Input Voltage is Minimum Input Voltage. In some applications, NTC Thermistor is bypassed with a timed relay after Inrush Current. Even though the thermistor is out of circuit during operation, it is best to select a thermistor that can handle steady state current, in case the relay fails.