Well, hot bus is a bus that is constantly energized with power from any source, i.e. battery or generator, when the rest of the system is "locked out" from the power source.
In my airplane as an example, emergency power is available when turning on the emergency power switch independent of the battery switch is in the on/off position. Emergency power is taken from the Battery Hot Bus (or known as the Battery Direct Bus).
Fuelling panel, stairs and emergency annunciator lights is typically powered from a Hot Bus.
Last edited by MD80rookie; 6th September 2010 at 16:27.
Reason: spelling