The present invention relates to a device operable electrically via a mains voltage connection, in particular without a ground wire connection, having a live element and having an application part, wherein the application part is insulated by a basic insulation with respect to the live element. In this respect, an insulation monitor is provided which monitors the quality of the basic insulation of the application part with respect to the live element. The present invention furthermore comprises a medical device having a heating module for heating a medical fluid, wherein the heating module comprises a heating element having a heating coil arranged on a first ceramic layer, wherein the heating element is arranged on a second ceramic layer, wherein the second ceramic layer advantageously forms a heating plate of the heating module.