Steep-fronted voltage transients produced by switching operations are a major source of insulation failure in machine windings. Determination of the severity of these transients is essential if machine insulation systems are to be designed correctly. However, the severity of these transients varies widely depending upon plant parameters and system configurations. Consequently, there is a need to establish, in general terms which plant parameters and system configurations lead to particularly severe transient conditions. Computer studies have been carried out to examine what factors determine the severity of switch-closing transients in a cable-connected motor system supplied from a complex source. The source-side network included full representation of the busbar and its section, multiple cable connections and facilities for transformer of infinite busbar primary supply. The load-side network included the motor cable and a ladder-network representation of the motor winding. The Fourier transform method was used for the solution method so that frequency-dependent variables of the cables could be fully incorporated in the solution. The studies were based on a single-phase system representation simulating first-pole-to-close conditions. Busbar lengths and configurations were found to be of fundamental importance in defining transient severity. Short-busbar lengths and parallel-busbar configurations gave rise to particularly severe transients. The effect of increasing the number of cables connected to the busbar was found to be not as severe as expected, due to the presence of the short-busbar subsections in between the cables. Stray capacitance local to the motor-controlling switch, although not usually taken into consideration in such studies, was found to be a factor of some importance. Motor cable length and motor parameters were found to be of lesser importance.