Describes method for calculating short-circuit currents in d.c. auxilliary systems in power plants and substations, which can be equipped with the following equipment, acting as short-circuit current sources:- rectifiers in three-phase a.c. bridge connection for 50 Hz;- stationary lead-acid batteries;- smoothing capacitors;- d.c. motors with independent excitation Provides a generally applicable method of calculation which produces results of sufficient accuracy on the conservative side. The contents of the corrigenda of February 1999 and March 2000 have been included in this copy.