The invention relates to a circuit arrangement for connecting a protective conductor to at least two liquid-conveying lines (11, 12), particularly to at least two liquid-conveying lines leading from inside a housing (1) of a medical appliance, particularly the housing of a blood treatment appliance, to the outside. The circuit arrangement comprises a plurality of protective devices (16A, 16B； 17A, 17B) for electrical contacting, which are designed such that each one can be used to create an electrical connection to a liquid circulating in the line. At least two protective devices (16A, 16B； 17A, 17B) for electrical contacting are associated with each liquid-conveying line (11, 12) in the circuit arrangement. Two protective measures are therefore taken for each liquid-conveying line. Furthermore, the protective devices (16A, 16B； 17A, 17B) of a liquid-conveying line (11； 12) are respectively electrically connected to another protective device (16A,16B；17A, 17B) of another liquid-conveying line (11； 12). The protective conductor concept according to the invention improves the safety of the patients and allows easy checking of the protective conductor connections.
