An electronic appliance powered by a power supply unit connected to a mains type electricity network, and for connection to a transmission line having two conductor elements and to a terminal in order to transfer data between the line and the terminal. The appliance has a front-end component connected to the line via an isolating transformer. Also, various additional components are connected to an electrical ground of the appliance. A discharge component is connected to the conductor elements of the line and becomes conductive in the event of a voltage surge due to a lightning strike. This eliminates the surge by establishing a flow of current from the line to electrical ground. A capacitive and/or resistive type divider component is interposed between the discharge component and electrical ground in order to co-operate with the power supply unit and/or one or more additional components to constitute a divider bridge.