Second factor is the minimum resistance required by NTC Thermistor. Minimum resistance required will vary from one application to another, depending on the line Voltage, peak Inrush Current and desired Inrush Current limitation due to fuse and circuit breaker ratings. As a rule of thumb, if the maximum allowable Inrush Current is not known either the diode bridge specifications or oscilloscope readings of Inrush Current will dictate the minimum resistance required by NTC Thermistor. Typically, 1/3rd of observed Inrush Current from oscilloscope readings is acceptable. MinR= Vpeak / Ilimit where MinR is Minimum Resistance required by NTC Thermistor at t=0 at 25ºC , Vpeak is Peak Voltage, and Ilimit is Desired Inrush Current limit.