OTLM device simultaneously measures conductor temperature, sag (icing), ambient temperature, humidity and current of power lines. Measurements are carried out directly at the OTLM fixing points on the OHL phase conductor and are transmitted to the OTLM Centre via available communication channels with the exact GPS time stamp. The current transformer (energy harvesting) and the supply unit provide the power supply for the operation without any other outside source of power supply (battery as an additional option). Housing is made of fire-resistant composite material for heavy ambient conditions. In case of communication failure data is stored locally in OTLM. Installation is simple and fast. The device can be installed on a conductor with a diameter from 15,00 mm and up to 45,00 mm.