One key difference between the Class 56 and the various preceding British locomotives produced during the 1950s and 1960s is the use of self-exciting alternators rather than direct current (DC) generators for the generation of both traction current and auxiliary supply. This change reportedly results in the power unit being considerably more robust, as well as greatly reducing the risk of flash-overs and other earth-related faults. Traction supply was rectified since the type employs DC traction motors. Much of the auxiliary apparatus, such as the compressors and traction motor blowers, were powered via the unrectified 3-phase AC output of the auxiliary alternator, and therefore run at a speed proportional to engine r.p.m.