Method for determining a mean time to failure of an electrical device, comprising: measuring temperatures by means of a temperature sensor during an operational time; determining a mean temperature value (AOTj) at which the electrical device has operated during an operational time from the measured temperatures during the operational time; determining a temperature range in which the determined mean temperature value (AOTj) is located, said range being bounded by a first temperature value which corresponds to a first predetermined value of mean time to failure and a second temperature value which corresponds to a second predetermined value of mean time to failure; determining an adjusted mean time to failure time (MTTF) of the electrical device based on said mean temperature value (AOTj), said first value of the temperature range, said second value of the temperature range, said first predetermined value of mean time to failure and said second predetermined value of mean time to failure; providing the first predetermined value mean time to failure and the second predetermined value of mean time to failure for a predetermined load condition of the electrical device which corresponds to a percentage of a maximum amount of power that can be supplied by a power supply of the electrical device, and wherein determining the adjusted mean time to failure comprises: applying the following expression: MTTF i = MTTF Tx − MTTF Tx − MTTF Ty ∗ AOT j − Tx Ty − Tx wherein: - Tx is the second (lower) value of the temperature range; - Ty is to the first (upper) value of the temperature range; - AOTj is the determined mean temperature value; - MTTF Tx is the predetermined second mean time to failure; - MTTF Ty is the predetermined first mean of time to failure; - MTTF i is the adjusted mean time to failure. wherein the method further comprises: determining a compensated operational time based on operational time and actual load of the electrical device; and comparing the compensated operational time to the adjusted mean time to failure; and/ or determining a time difference between the adjusted mean time to failure and the compensated operational time. measuring temperatures by means of a temperature sensor during an operational time; determining a mean temperature value (AOTj) at which the electrical device has operated during an operational time from the measured temperatures during the operational time; determining a temperature range in which the determined mean temperature value (AOTj) is located, said range being bounded by a first temperature value which corresponds to a first predetermined value of mean time to failure and a second temperature value which corresponds to a second predetermined value of mean time to failure; determining an adjusted mean time to failure time (MTTF) of the electrical device based on said mean temperature value (AOTj), said first value of the temperature range, said second value of the temperature range, said first predetermined value of mean time to failure and said second predetermined value of mean time to failure; providing the first predetermined value mean time to failure and the second predetermined value of mean time to failure for a predetermined load condition of the electrical device which corresponds to a percentage of a maximum amount of power that can be supplied by a power supply of the electrical device, and wherein determining the adjusted mean time to failure comprises: applying the following expression: MTTF i = MTTF Tx − MTTF Tx − MTTF Ty ∗ AOT j − Tx Ty − Tx wherein: - Tx is the second (lower) value of the temperature range; - Ty is to the first (upper) value of the temperature range; - AOTj is the determined mean temperature value; - MTTF Tx is the predetermined second mean time to failure; - MTTF Ty is the predetermined first mean of time to failure; - MTTF i is the adjusted mean time to failure. wherein the method further comprises: determining a compensated operational time based on operational time and actual load of the electrical device; and comparing the compensated operational time to the adjusted mean time to failure; and/ or determining a time difference between the adjusted mean time to failure and the compensated operational time. applying the following expression: MTTF i = MTTF Tx − MTTF Tx − MTTF Ty ∗ AOT j − Tx Ty − Tx wherein: - Tx is the second (lower) value of the temperature range; - Ty is to the first (upper) value of the temperature range; - AOTj is the determined mean temperature value; - MTTF Tx is the predetermined second mean time to failure; - MTTF Ty is the predetermined first mean of time to failure; - MTTF i is the adjusted mean time to failure. - Tx is the second (lower) value of the temperature range; - Ty is to the first (upper) value of the temperature range; - AOTj is the determined mean temperature value; - MTTF Tx is the predetermined second mean time to failure; - MTTF Ty is the predetermined first mean of time to failure; - MTTF i is the adjusted mean time to failure. wherein the method further comprises: determining a compensated operational time based on operational time and actual load of the electrical device; and comparing the compensated operational time to the adjusted mean time to failure; and/ or determining a compensated operational time based on operational time and actual load of the electrical device; and comparing the compensated operational time to the adjusted mean time to failure; and/ or determining a time difference between the adjusted mean time to failure and the compensated operational time.