Abstract: A model railway or road vehicle installation in which vehicle-mounted electric drive motors are supplied through contact with track conductors, including a power supply providing an intrinsically safe a.c. component of such frequency and amplitude as to be capable of breaking down any contact inhibiting dielectric layer of dust, grease, metal oxide etc. on the track conductors, in addition to the normal d.c. component powering the vehicle. An automatic arrangement suppresses the a.c. component so long as good electrical contact is maintained so that the a.c. component is provided only when necessary. For facilitating slow speed operation, the d.c. supply is pulsed with a variable mark to space ratio dependent upon the desired vehicle speed thereby to maintain the torque output of the vehicle motor.