Abstract: A method and apparatus for determining the thermal capacity of overhead power lines is disclosed. The apparatus includes two rods of similar diameter and material properties to the line to be rated. One of the rods has a heater inside that dissipates a known amount of energy approximately equal to what the line loses during operation at the static rating. The rods are oriented parallel to the line and the temperature of each is measured. Using this information and standard equations governing the cooling of power lines, a very accurate, real-time reading of the line's thermal capacity is generated.