First, the nature of equivalent circuits and the alternative electric or magnetic equivalents for any electromagnetic system are examined. In the remaining Sections, steady-state and symmetrical sudden short-circuit conditons are analysed for the3-phase synchronous, the 3-phase induction and the compounded d.c. machine, using the magnetic-equivalent representation. Results are obtained more easily than by the conventional procedure. Also, since the method of analysis is the same for each of the cases considered, results obtained for one type of machine can often be applied to another and the approach is truly general.