a dc control circuit supplies direct current of either polarity at a high or a low level to a crane hoist or the like via a single bus bar to control up , down , low or high speed functions . a network of diodes and ganged switches at a remote control panel supplies the selected level and direction of current to the bus bar while a control circuit moving with the powered equipment responds to the voltage level and polarity picked off of the bus bar by means of a high voltage responsive relay coil circuit and dual , parallel , diode , relay coil circuits responsive to polarity .