Apparatus for monitoring the temperature of a high voltage conductor includes an electrically and thermally conductive fixture for attachment to a high voltage conductor, and a high voltage insulator having a high voltage end and a reference potential end. The insulator is connected at the high voltage end to the fixture. The insulator contains a fiber optic cable in a fiber optic cable passageway from the reference potential end to the high voltage end. The cable extends beyond the insulator. An optical temperature sensor head is optically coupled to the cable the high voltage end. The sensor head includes a sensor crystal which transmits light that varies with temperature of the sensor crystal. An electrically and thermally conductive enclosure enclosing the sensor head is supported in the fixture for thermally conductive contact with the high voltage conductor effective to couple the temperature of the high voltage conductor to the sensor crystal. An optoelectrical unit powers and detects the optic signal carrying the information about the temperature of the high voltage conductor.