Abstract: Recent developments in switching by means of electronic devices such as thyristors offer more possibilities to assist commutation in DC generators or motors. It is this latter aspect that has been utilised in an attempt to suppress the sparking that occurs between the trailing edge of a brash and the commutator of direct current machines. The semiconductor device chosen for the investigation was the asymmetric thyristor is used to switch into circuit an auxiliary brush whenever sparking occurs. The auxiliary brush is positioned trailing the main brush and electrically isolated by a small intervening layer of insulation. The auxiliary brush provides a path for the uncommutated current and associated energy to be dissipated in series connected resistors. The research has addressed the design of the brushes, brush gear, thyristor triggering and spark energy dissipating resistors. The realisation and testing of the system shows promising results.