Abstract: In order to minimize the initial in-rush produced on first energisation of a polyphase induction motor (10), careful control is exercised over the firing of controlled switching means (11) connected in series with each of the supply phases (A, B, C) or motor windings. This control includes effecting an initial selective firing of the switching means (11) such as to cause current to flow between two only (B,C) of the supply phases, the firing being timed to occur such that the voltage between these two phases (B,C) is decreasing in value at the moment of firing. Thereafter, the switching means (11) are sequentially fired in a manner resulting in the progressive increase in the angle of conduction of each switching means (11).