nuckolls.bob(at)aeroelect
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 Posted: Thu Mar 10, 2022 12:09 pm Post subject: Z101b Fusing Question. |
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At 09:04 AM 3/10/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: Jeffrey Cohen <jcohen(at)post.com>
I am implementing Z101b on my experimental RV7 Aircraft.
Why does Z101b shows NO fuse or fusible Link Wire from the FAT WIRE TIE POINT to the ENG BUS ALT FEED RELAY?
Same question, why no fuse for the wire from the BATTERY CONTACTOR to the DIODE BRIDGE NTE53016?
Any thoughts why Bob did not fuse protect these wires? With a short, put 100A through a 12GA or 14GA wire, and it will get red hot and light something else on fire.
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Wires that are part of the distribution system (fat wires)
are generally heavy, short and mechanically well protected
from severe faults. Many such examples can be found on
a variety of aircraft of all sizes. In TC aircraft like
a C172, you don't find circuit protection on battery,
starter and bus feeders. We DO see protection on battery
end of alternator b-leads in deference to the potential
for hard fault inside an alternator . . . exceedingly
rare these days but the practice persists in both cars
and aircraft.
As to the hypothetical 100A 'short' . . . study the
mechanics of your system installation to deduce how
such a short might happen?
Consider the extensive bus-bar structures behind
the breaker panels of many aircraft . . . breakers
fed by fat wires with mechanically and electrically
low/zero risk for hard faults.
Some of your airplane's components are considered
by design and practice to be free of risk for
catastrophic failure. Judiciously installed fat-wire
feeders are among those components. On the other hand,
wires that branch out from bus bars driven by those
feeders are at greater risk due to relatively small
size, real estate they traverse and appliances they
power . . . each appliance feeder gets its own
appropriately sized fuse/breaker.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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