A device for electric connection to an energy supply conductor for medium and high voltage, including: a voltage-carrying element; a tubular outer shell formed by a thermoplastic polymer and connected to the voltage carrying element; wherein the voltage-carrying element extends in a longitudinal direction of the tubular shell, and wherein, at least along a part of the length of the voltage-carrying element, the outer shell extends in a longitudinal direction with a space between its inner periphery and an outer periphery of the voltage-carrying element; the outer shell being provided with an outer contact surface to be connected to a wall of a gas-tight container somewhere along the part of the length of the voltage-carrying element; wherein the outer shell is arranged so as to separate said space from an atmosphere outside a container to which the device may be connected. At least along a section of the part of the length of the voltage-carrying element the space is filled with a filler of an electrically insulating material other than that of the outer shell, the filler completely filling the space along the section.