An apparatus for connecting an electrical device to a high-voltage power grid with a leadthrough plug-in bushing which has a hollow receiving section which extends in a plug-in direction and is composed of an electrically nonconductive insulating material, wherein a metallic contact part is arranged on a closed end region of the receiving section, which metallic contact part extends through the insulating material of the receiving section or lengthens said receiving section in the direction of the closed end region. The apparatus can be assembled and serviced in a simple, quick and therefore cost-effective manner. The receiving section is equipped with a current sensor which is designed to detect an electric current flowing across the metallic contact part.