Underground insulated telecommunication cables must be impregnated with a hydrophobic material in order to prevent water penetration damage. To do so, the cable wire bundle must be heated to a temperature of 60 to 90 degrees C to ensure proper fluidity of the hydrophobic material that must fill the free spaces between the copper wires of the telephone cable. This paper described the microwave heating method of the wires before their impregnation. A cylindrical applicator was designed to perform a telephone bundle heating test. 800 W of microwave power were used on a telephone cable made up of 800 wires of 0.4 mm in diameter. A uniform heating was obtained throughout the section. Microwave heating was also found to be 53 per cent more energy efficient than hot air heating. 4 refs., 4 figs.