This part of IEC 1660 describes the mechanical and thermal effects on rigid conductors caused by short-circuit currents in d.c. auxiliary installations in power plants and substations. Such systems may contain the following items of equipment which act as sources, as well as contribution to the short-circuit currents: 1) Rectifiers in three-phase a.c. bridge connection for 50 Hz. 2) Stationary lead-acid batteries. 3) Smoothing capacitors. 4) D.C. motors with independent excitation.