As SMOC says, the displayed set up is not possible
All Boeings I have known from B707 on have a protection which trips off EXT PWR when a GEN comes on line to that bus. End of story. The diagram reminds me of something out of a training leaflet to show what the indications are for various power breakers made or open but not an operational scenario.
The B747 electrical system is fairly simple. 4 AC buses, each powered by an engine driven alternator and 4 DC buses fed by TRUs. Both the AC and DC systems are tied/paralleled to avoid out of phase stuff and to load share. Some important equipment is fed from stand by, essential or direct from the ships battery depending on its importance. These buses are sourced from whatever power is available, generally automatically. The APU just runs the ship on the ground prior to engine start. NB this is VERY simplified!!! It just goes to show that Westinghouse got it right first time in the 1950s!