Conductor temperature imposes a significant restriction on transmission grid loads. The limits currently defined are based on seasonal extreme weather conditions, which frequently result in unused capacities which could be utilised to operate the lines even in overload situations. The aim of this project is to develop a more accurate way of estimating available line capacity. To do this it is necessary to accurately determine the effective conductor temperature and, using models, lab experiments and field measurements, examine its changes under different weather conditions and current flows. Based on this, the maximum possible volume of electricity or the maximum possible operating time for a specific overload can be determined, taking into account the current weather situation and the length and deterioration of the line.