Thermal-mechanical fatigue assessment systems and methods include a controller operable to estimate a temperature of the conductor having a non-linear resistance based on an ambient temperature input and a current input for current flow through the conductor when connected to an energized electrical power system. A state of fatigue of the conductor may be assessed in view of an estimated first temperature differential between the conductor and an arc extinguishing medium surrounding the conductor, an estimated temperature differential between the temperature of the arc quenching medium and the ambient temperature, and the estimated temperature of the conductor.