A method of tracking thermal age of a heating cable in a system including a control unit that monitors the heating cable, the method comprising: receiving, by the control unit, a thermal aging curve associated with a type of the heating cable, the thermal aging curve being generated by: applying a thermal aging process to an example cable having the type; at discrete data points in time during the thermal aging process, collecting from the example cable a test cable signal generated by passing a line current through the example cable; extracting, from the test cable signal collected at each data point, a plurality of amplitude components each representing a corresponding amplitude of one of a plurality of harmonic frequencies of the line frequency; for each data point, calculating one or more ratios of one or more pairs of the amplitude components; storing at least one of the ratios corresponding to each data point; and correlating each of the stored ratios with a corresponding location of a plurality of locations defining the thermal aging curve; collecting, by the control unit, a cable signal generated by passing a line current through the heating cable; extracting, from the cable signal by the control unit, spectral information comprising a line frequency, one or more harmonic frequencies of the line frequency, and an amplitude component for each of the line frequency and harmonic frequencies; calculating, by the control unit, one or more measured functional dependencies between one or more pairs of the harmonic frequency amplitudes; and comparing, by the control unit, one or more of the measured functional dependencies to one or more of the stored ratios to determine a current location of the heating cable on the thermal aging curve, the current location indicating the thermal age of the heating cable. receiving, by the control unit, a thermal aging curve associated with a type of the heating cable, the thermal aging curve being generated by: applying a thermal aging process to an example cable having the type; at discrete data points in time during the thermal aging process, collecting from the example cable a test cable signal generated by passing a line current through the example cable; extracting, from the test cable signal collected at each data point, a plurality of amplitude components each representing a corresponding amplitude of one of a plurality of harmonic frequencies of the line frequency; for each data point, calculating one or more ratios of one or more pairs of the amplitude components; storing at least one of the ratios corresponding to each data point; and correlating each of the stored ratios with a corresponding location of a plurality of locations defining the thermal aging curve; applying a thermal aging process to an example cable having the type; at discrete data points in time during the thermal aging process, collecting from the example cable a test cable signal generated by passing a line current through the example cable; extracting, from the test cable signal collected at each data point, a plurality of amplitude components each representing a corresponding amplitude of one of a plurality of harmonic frequencies of the line frequency; for each data point, calculating one or more ratios of one or more pairs of the amplitude components; storing at least one of the ratios corresponding to each data point; and correlating each of the stored ratios with a corresponding location of a plurality of locations defining the thermal aging curve; collecting, by the control unit, a cable signal generated by passing a line current through the heating cable; extracting, from the cable signal by the control unit, spectral information comprising a line frequency, one or more harmonic frequencies of the line frequency, and an amplitude component for each of the line frequency and harmonic frequencies; calculating, by the control unit, one or more measured functional dependencies between one or more pairs of the harmonic frequency amplitudes; and comparing, by the control unit, one or more of the measured functional dependencies to one or more of the stored ratios to determine a current location of the heating cable on the thermal aging curve, the current location indicating the thermal age of the heating cable.