A residual-current circuit breaker includes a core-balance transformer, a first conductor and a second conductor of an electrical supply system which is to be protected being routed through the core-balance transformer, and a secondary winding being arranged on the core-balance current transformer. The secondary winding is connected to a release by circuitry. A test circuit connecting the first conductor and the second conductor has at least a first test resistor and a reset button, in order to provide accurate checking of an ability of residual current tripping to function, the test circuit has a second test resistor arranged in series with the first test resistor by circuitry. The second test resistor is bridged by a bypass line that is routed through the core-balance transformer and at least one first voltage dependent resistor is arranged in the bypass line by circuitry.