Cribbly Dock, it all depends upon the position of the BUS TIE switch on the ELEC panel. If OFF, neither the Bus Tie Contactors nor the System Isolation Contactor can be controlled to close. Therefore the APU Generator cannot connect to either bus, good or bad. During the Smoke procedure, the switch is selected OFF to isolate the buses, so the only way to power a bus is from it's own generator.