Method for determining a parameter for mapping a thermal load of an electrical equipment (9, 11, 19, 21) for a determination time on the basis of an ambient temperature of the electrical equipment (9, 11, 19, 21) at the determination time and a determined value of a thermal operating parameter of the equipment at the determination time by means of a first mathematical model, which describes a dependence of the thermal operating parameter of the equipment at a calculation time on the ambient temperature of the electrical equipment (9, 11, 19, 21) at the calculation time and the electrical utilization of the equipment (9, 11, 19, 21) at the calculation time, wherein the parameter for the time of determination is determined as the equivalent electrical utilization of the electrical equipment (9, 11, 19, 21), in which the first mathematical model predicts the value of the thermal operating parameter of the electrical equipment determined for the time of determination, taking into account the ambient temperature at the time of determination. wherein the determined thermal operating parameter of the electrical equipment (9, 11, 19, 21) is determined at the time of determination by means of a second mathematical model which describes a dependence of the thermal operating parameter of the electrical equipment (9, 11, 19, 21) on a course of an ambient temperature of the electrical equipment (9, 11, 19, 21), a course of an electrical utilization of the equipment (9, 11, 19, 21) and an initial value for the thermal operating parameter, wherein a value for the thermal operating parameter at an initial point in time is used as the initial value for the thermal operating parameter, wherein the value for the thermal operating parameter was preferably measured at the electrical equipment (9, 11, 19, 21) at the initial point in time, wherein the course of the ambient temperature describes the course of the ambient temperature of the equipment (9, 11, 19, 21) between the initial time and the time of determination, and wherein the course of the electrical utilization of the equipment (9, 11, 19, 21) describes the course of the electrical utilization of the equipment (9, 11, 19, 21) between the initial time and the determination time, characterized in that a course of the characteristic variable is determined for an evaluation period, which comprises a plurality of evaluation times, in that a determined value for the thermal operating parameter of the electrical equipment (9, 11, 19, 21) is determined for each evaluation time as a determination time by means of the second mathematical model and the characteristic variable for the respective evaluation time as a determination time is determined by means of the first mathematical model on the basis of the value thus determined for the thermal operating parameter of the electrical equipment (9, 11, 19, 21). wherein the parameter for the time of determination is determined as the equivalent electrical utilization of the electrical equipment (9, 11, 19, 21), in which the first mathematical model predicts the value of the thermal operating parameter of the electrical equipment determined for the time of determination, taking into account the ambient temperature at the time of determination. wherein the determined thermal operating parameter of the electrical equipment (9, 11, 19, 21) is determined at the time of determination by means of a second mathematical model which describes a dependence of the thermal operating parameter of the electrical equipment (9, 11, 19, 21) on a course of an ambient temperature of the electrical equipment (9, 11, 19, 21), a course of an electrical utilization of the equipment (9, 11, 19, 21) and an initial value for the thermal operating parameter, wherein a value for the thermal operating parameter at an initial point in time is used as the initial value for the thermal operating parameter, wherein the value for the thermal operating parameter was preferably measured at the electrical equipment (9, 11, 19, 21) at the initial point in time, wherein the course of the ambient temperature describes the course of the ambient temperature of the equipment (9, 11, 19, 21) between the initial time and the time of determination, and wherein the course of the electrical utilization of the equipment (9, 11, 19, 21) describes the course of the electrical utilization of the equipment (9, 11, 19, 21) between the initial time and the determination time, characterized in that a course of the characteristic variable is determined for an evaluation period, which comprises a plurality of evaluation times, in that a determined value for the thermal operating parameter of the electrical equipment (9, 11, 19, 21) is determined for each evaluation time as a determination time by means of the second mathematical model and the characteristic variable for the respective evaluation time as a determination time is determined by means of the first mathematical model on the basis of the value thus determined for the thermal operating parameter of the electrical equipment (9, 11, 19, 21).