A method for identifying an outgoing circuit having an earth fault in a three-phase power supply system, wherein a zero voltage and zero currents of outgoing circuits are measured and stored, where a space vector representation of the zero voltage and an active component of the space vector representation of zero currents are determined and, after determining an earth fault at a first time, a second time at which the space vector representation of the zero voltage has a local minimum and a third time at which the space vector representation of the zero voltage has a local maximum are determined, where the trapezoidal sum of the active component of the space vector representation of the zero currents is determined and used to determine the outgoing circuit having the earth fault via comparison with a predefined variable threshold value, an earth fault being determined if this threshold value is exceeded.