>Bob, I recently bought a copy of the AeroElectric Connection and think
>it's a great resource...I have one question and I'm sure it's in the
>book somewhere (I just can't find it), but what is the difference
>between an Essential Bus and the other power distribution buses?
>
>Thanks for the primer!
>
You're welcome. I'm pleased that you find the work useful!
Not much . . . bus structures can be divided up for
a variety of reasons. The items powered from any particular
bus will have something in common. For example, a fuseblock
or row of breakers might be feed from the always hot side
of a battery contactor to supply needs of dome lights, clocks,
engine hour-meters, electronic ignition, . . . any item that
you want to have powered EVEN IF the rest of the electrical
system is shut down.
In the case of an ESSENTIAL bus, I encourage builders to
consider the electrical items most useful in getting to
intended destination. These must certainly include minimal
lighting, primary nav radio, turn coordinator, a voltmeter
and perhaps engine boost pump. The goal is to define a very
low energy budget for utilizing a finite amount of energy
on board in terms of battery capacity.
I discourage calling it an EMERGENCY bus . . . if airplanes
are properly designed and operated, electrical emergencies
don't happen. This is why we have an ESSENTIAL bus - to
keep an electrical event from becoming an EMERGENCY. Some
builders still call it their "avionics" bus and include
the now outdated "avionics master" switch in the normal
feed path. Note however that the essential bus in my drawings
have two, independent power pathways to get electrons to the
most needed devices.
Hope this helps . . .
Bob . . .
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