A cable assembly for a flame sensor apparatus includes an inner conductor electrically connected to a photodiode that generates a current. The inner conductor transmits the current from the photodiode. A first insulating layer circumferentially surrounds the inner conductor. The first insulating layer includes a mineral insulation material. An inner sheath circumferentially surrounds the first insulating layer. The inner sheath includes an electrically conductive material. A second insulating layer circumferentially surrounds the inner sheath. The second insulating layer includes a mineral insulation material. An outer sheath circumferentially surrounds the second insulating layer. The outer sheath includes an electrically conductive material. The cable assembly is for use in temperatures up to about 300 degrees Celsius or greater. A method of attaching a cable assembly for a flame sensor apparatus.