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Question on Z-13 in revision 12A

 
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jason(at)jasonbeaver.com
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PostPosted: Wed Mar 17, 2010 1:52 am    Post subject: Question on Z-13 in revision 12A Reply with quote

I noticed that the e-bus alternate feed design changed from revision 11 to revision 12A. In revision 11, the alternate feed path used a 7A fuse and was wired with 16AWG and a 20AWG fuselink. In 12A, it uses an 15A fuse and is wired with 14AWG, but still uses a 20AWG fuselink. Is this correct, or should it now use an 18AWG fuselink?

Also at 7A, the formally specified 16AWG wire will already have a 10�C temp rise, and the 20AWG fuselink would have a 35�C temp rise. If we size the wires for a 15A feed at the same temperature rise, shouldn't we use a 10AWG wire with a 14AWG fuselink? At 15A, the currently specified 14AWG already has a 35�C temp rise and have no idea how hot an 18AWG or 20AWG fuselink would be.

Am I missing something?

thanks,

jason


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nuckolls.bob(at)aeroelect
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PostPosted: Wed Mar 17, 2010 5:57 am    Post subject: Question on Z-13 in revision 12A Reply with quote

At 02:11 AM 3/17/2010, you wrote:
Quote:


I noticed that the e-bus alternate feed design
changed from revision 11 to revision 12A. In
revision 11, the alternate feed path used a 7A
fuse and was wired with 16AWG and a 20AWG
fuselink. In 12A, it uses an 15A fuse and is
wired with 14AWG, but still uses a 20AWG
fuselink. Is this correct, or should it now use an 18AWG fuselink?

Also at 7A, the formally specified 16AWG wire
will already have a 10�C temp rise, and the
20AWG fuselink would have a 35�C temp rise. If
we size the wires for a 15A feed at the same
temperature rise, shouldn't we use a 10AWG wire
with a 14AWG fuselink? At 15A, the currently
specified 14AWG already has a 35�C temp rise and
have no idea how hot an 18AWG or 20AWG fuselink would be.

Am I missing something?

Sort of. The Z-figures are NOT detailed wiring diagrams for
your airplane. They're suggestions for architectures that
offer failure tolerant solutions to design goals.

The sizes of batteries, alternators, wires, breakers, contactors,
relays, switches and the quantities of such things are dependent
on your particular suite of components.

While strict observance of any suggested wire sizes in a Z-figure
will yield a 'functional' system, it may not conform to the
best we know how to do. Check out examples of e-bus architectures
across the various Z-figures, they're not identical. And don't
get wrapped around the AC43-13 wire-sizing exercise axle. Suggest
you size wires using suggested current ratings in the chart
on page 8-8. Keep in mind too that the 'ratings' are EXCEEDINGLY
conservative. 20A through a 22AWG wire doesn't smoke it. See:

http://aeroelectric.com/Pictures/Wire/22AWG_20A.pdf

Finally, if a fusible link is to FUNCTION as a fusible
link, then it MUST be thermally stressed at some level
much greater than the feeder it protects, so yes, it
will run warmer than the feeder.

Bob . . .


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