Vattenfall (Swedish State Power Board) was the first company to use the thermographic technique for inspection of high tension electrical equipment. The method has mainly been used for inspection of switchgear- and transformer stations. Recently Vattenfall has introduced a high resolution imager mounted in a helicopter for inspection ofjoints in the transmission lines. The inspection programme has started due to some phase dropping caused by increased resistance in the joints. The Rank Taylor Hobson Talytherm 8-1000 camera is mounted in a vibration free rig under the fuselage of the helicopter. The inspector, seated alongside the pilot, controls all the functions of the camera, together with the viewing angle pan and tilt, with the use of a single control panel. Mounted in front of the inspector is a 9" monitor on which the thermal image is displayed. The complete inspection is recorded on a S-VHS video tape for later retrieval together with comments and inspection data such as line identification, tower number, load and weather conditions. A HP-computer with the Talytherm T.E.M.P.S. Imager/Data analysing system is used to determine over-temperature compared with the transmission line. As the reconditioning criteria is based on the joint resistance an FEM computer programme has been developed to calculate the resistance using the temperature pattern on the surface of the joint and the connecting lines. The temperature pattern based on data such as: geometrical data, resistance, load, wind speed and direction can be calculated with the programme. The resistance can then be determined by comparing the results with the measured temperature pattern by the thermal inspection.