747-400 Main Deck Cargo Handling

[QAVION]

A few days ago, whilst in the cockpit of an SQ 747-400 Freighter, I noticed that APU Generator #2 was AVAILable, but not selected whilst main deck cargo was being loaded.

Is it standard practice/a precautionary measure to evenly distribute the electrical load by doing this... or is there actually some kind of airplane logic preventing both the right sync bus and the main deck cargo handling systems being fed by APU gen #2 at the same time? I couldn't find any reference to it in the -400 Maintenance Manual (Doors or Elec Chapters).

Thanks.
Q.