A contactless inductive power distribution system operating at 10 KHz has a self tuning resonant power supply connected to a resonant primary conductive path 10110, 10111 comprising a pair of parallel litz wire conductors 10110, 10111 each encapsulated within an insulated sheath and supported on a structural monorail beam 10101 on which a plurality of electric vehicles can run. Each vehicle has an electric motor (not shown) capable of deriving power from a resonant pick-up coil 10115 wound on a ferrite core 10102 mounted on the vehicle in close proximity to the primary conductors 10110, 10111. Each vehicle also has switching means 10116 capable of preventing a lightly loaded vehicle from presenting a reduced load to the resonant primary. As shown, this comprises an isolating coil 10116 having a switch (not shown) to switch the coil between an open circuit and a short circuit, so that when the switch is switched from one state to another state the power coupled between the primary conductive path 10110, 10111 and the pick-up coil 10115 is changed.