This paper describes methods of calculating the peak temperature rise of the armature winding of a dc servo motor when operated on a specific duty cycle and for torque values greater than rated. It also defines the relationship of the maximum allowable time ON (tR) for a desired output torque such that the peak temperature rise will not exceed the temperature rating of the insulation thus ensuring adequate insulation life. A new approach of specifying these duty cycle characteristics is suggested which can be used to find the maximum time ON (tR) for a given torque as well as the peak temperature rise for any length of time ON (t1). The use of these characteristics can be extended from repetitive cycles to duty cycles where output torque requirements within a cycle are varying. This analytical approach is supported by experimental data.