Abstract: The invention relates to a process for operating a lead-in-device receiving a conductor which passes through the cover of an electrical precipitation apparatus down to its electrode system. A portion of the conductor is encircled by an insulator which is radially spaced therefrom and of which the upper end provides support for a structural component having the conductor gas tightly passed therethrough. The space inside the insulator receives a sealing gas which is maintained under a pressure higher than that prevailing in the electrical precipitation apparatus. The sealing gas used for operating the device is a gas mixture consisting of an inert gas and at least 10 volume % of methane.