Method for identifying transient-type earth faults in a electrical network and selectively tripping the faulty portion, in which electrical network there are several branch lines (A - D) connected to a main line, and in which • the residual voltage U0 and the zero current 10 of at least one branch line (A-D) are measured to create zero-current and residual voltage signals, • the measured zero-current and residual-voltage signals are sampled continuously at a selected sampling frequency, and • the samples obtained are buffered periodically in a zero-current buffer memory and a residual-voltage buffer memory, respectively, • each recorded cycle is analysed using the buffered data, • a transient spike is identified as a fault candidate, if current and voltage spikes in different directions are observed according to a selected criterion, characterized in that, in the method • each absolute maximum value (I0max) is retrieved from the samples of the zero-current buffer memory as a current spike and its index (i) in this buffer memory, • the selected voltage data is retrieved from the residual-voltage buffer memory using the value of the index (i), • a value depicting the admittance-delta (INADMIT) is calculated as follows for the transient spike: • the differences are formed from the samples of the zero-current buffer memory and the samples of the residual-voltage buffer memory using the said index (i) and its chosen offset value (i - 4; i + 4), i) wherein the zero current's 10 difference DELTAI0 is calculated from the samples of the zero-current buffer memory and the residual voltage's U0 difference DELTAUO is calculated from the samples of the residual-voltage buffer memory, and ii) the admittance-delta INADMIT is calculated as the ratio DELTAI0/DELTAU0, • the polarity of the admittance-delta (INADMIT) of each spike is determined, with the aid of which each spike is classified as a forward-direction or reverse-direction spike using selected criteria, and • the fault candidate is ascertained to be a branch-line (A-D) transient earth fault when a forward spike is detected in the branch line and a selected additional criterion it met, which criterion is related with detection of a second spike or related with the stability of the residual voltage, within selected time (FWDreset) from the detection of said forward spike, and a selective tripping is performed. • the residual voltage U0 and the zero current 10 of at least one branch line (A-D) are measured to create zero-current and residual voltage signals, • the measured zero-current and residual-voltage signals are sampled continuously at a selected sampling frequency, and • the samples obtained are buffered periodically in a zero-current buffer memory and a residual-voltage buffer memory, respectively, • each recorded cycle is analysed using the buffered data, • a transient spike is identified as a fault candidate, if current and voltage spikes in different directions are observed according to a selected criterion, • each absolute maximum value (I0max) is retrieved from the samples of the zero-current buffer memory as a current spike and its index (i) in this buffer memory, • the selected voltage data is retrieved from the residual-voltage buffer memory using the value of the index (i), • a value depicting the admittance-delta (INADMIT) is calculated as follows for the transient spike: • the differences are formed from the samples of the zero-current buffer memory and the samples of the residual-voltage buffer memory using the said index (i) and its chosen offset value (i - 4; i + 4), i) wherein the zero current's 10 difference DELTAI0 is calculated from the samples of the zero-current buffer memory and the residual voltage's U0 difference DELTAUO is calculated from the samples of the residual-voltage buffer memory, and ii) the admittance-delta INADMIT is calculated as the ratio DELTAI0/DELTAU0, i) wherein the zero current's 10 difference DELTAI0 is calculated from the samples of the zero-current buffer memory and the residual voltage's U0 difference DELTAUO is calculated from the samples of the residual-voltage buffer memory, and ii) the admittance-delta INADMIT is calculated as the ratio DELTAI0/DELTAU0, • the polarity of the admittance-delta (INADMIT) of each spike is determined, with the aid of which each spike is classified as a forward-direction or reverse-direction spike using selected criteria, and • the fault candidate is ascertained to be a branch-line (A-D) transient earth fault when a forward spike is detected in the branch line and a selected additional criterion it met, which criterion is related with detection of a second spike or related with the stability of the residual voltage, within selected time (FWDreset) from the detection of said forward spike, and a selective tripping is performed.