A method in the manufacturing of an insulated electric high voltage DC termination or joint comprising the step of: - providing an insulated electric high voltage DC cable comprising a high voltage DC conductor, a polymer based insulation system surrounding the high voltage DC conductor, the polymer based insulation system comprising an insulation layer and a semiconducting layer surrounding the insulation layer, and a grounding layer surrounding the semiconducting layer; - removing the grounding layer and the semiconducting layer in at least one end portion of the high voltage DC cable, thereby exposing the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable, - temporarily covering the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable by a cover impermeable to at least one substance present in the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable in a non-homogenous distribution; - subjecting the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable for a heat treatment procedure, while being covered by the cover, thereby equalizing the concentration of the at least one substance in the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable; - removing the cover; and - mounting a pre-equalized field grading adapter or joint body in the at least one end portion of the high voltage DC cable, wherein the field grading adapter or joint body is pre-equalized by means of - mounting the field grading adapter or joint body in an end portion of a piece of cable having an exposed insulation layer with a similar composition as the insulation layer of the polymer based insulation system of the high voltage DC cable, thereby covering the insulation layer of the piece of cable; - subjecting the field grading adapter or joint body to a heat treatment procedure such that one or more substances from the insulation layer of the piece of cable diffuse into the field grading adapter or joint body; and - removing the field grading adapter or joint body from the piece of cable and covering the inner surface of the field grading adapter or joint body with a cover, which is impermeable to the one or more substances diffused into the field grading layer until the field grading adapter or joint body is mounted in the at least one end portion of the high voltage DC cable. - providing an insulated electric high voltage DC cable comprising a high voltage DC conductor, a polymer based insulation system surrounding the high voltage DC conductor, the polymer based insulation system comprising an insulation layer and a semiconducting layer surrounding the insulation layer, and a grounding layer surrounding the semiconducting layer; - removing the grounding layer and the semiconducting layer in at least one end portion of the high voltage DC cable, thereby exposing the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable, - temporarily covering the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable by a cover impermeable to at least one substance present in the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable in a non-homogenous distribution; - subjecting the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable for a heat treatment procedure, while being covered by the cover, thereby equalizing the concentration of the at least one substance in the insulation layer of the polymer based insulation system in the at least one end portion of the high voltage DC cable; - removing the cover; and - mounting a pre-equalized field grading adapter or joint body in the at least one end portion of the high voltage DC cable, - mounting the field grading adapter or joint body in an end portion of a piece of cable having an exposed insulation layer with a similar composition as the insulation layer of the polymer based insulation system of the high voltage DC cable, thereby covering the insulation layer of the piece of cable; - subjecting the field grading adapter or joint body to a heat treatment procedure such that one or more substances from the insulation layer of the piece of cable diffuse into the field grading adapter or joint body; and - removing the field grading adapter or joint body from the piece of cable and covering the inner surface of the field grading adapter or joint body with a cover, which is impermeable to the one or more substances diffused into the field grading layer until the field grading adapter or joint body is mounted in the at least one end portion of the high voltage DC cable.