Fourth factor is the ambient temperature. Ambient Temperature will dictate if there is a need for De-rating of Resistance and/or De-rating of Steady State Current. Rated resistance of NTC Thermistor is at 25ºC, so de-rating of resistance rating will be needed for ambient temperatures above 25ºC, as the resistance of the thermistor will be lower. Ametherm R/T curves will dictate how much de-rating is needed. Figure 1 is used to de-rate steady state current shown here, between 0ºC and 65ºC there is no De-rating necessary.