nuckolls.bob(at)aeroelect
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 Posted: Wed Sep 16, 2015 10:32 am Post subject: Alternator B-lead circuit protection |
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At 03:41 AM 8/7/2015, you wrote:
| Quote: | --> AeroElectric-List message posted by: Dan Charrois <dan(at)syz.com>
Hi everyone. I have a quick question with regards to protecting alternator B-leads.
A lot of people do so with ANL fuses, yet I know some aircraft (like my C150) do so with a circuit breaker. Of course, a disadvantage of the ANL is that if it blew while on a trip, after fixing whatever caused the problem, a person would have to source a new fuse which could result in the aircraft being grounded waiting for one to be shipped (are ANL fuses that easy to find? |
B-lead protection is a legacy design philosophy with
roots dating back to generators . . . it pay homage
to failure mode effects analysis rules that ASSUMES
that even unthinkable/unlikely thing will happen
and mitigates the effects.
99.999% of all circuit breakers and fuses installed
on airplanes go the lifetime of the airplane NEVER
being tasked with saving a wire at risk for fault,
overheating and fire. Yet, we have installed tons
of such devices on airplanes from C-140 to B-747
because it's 'never been a bad thing to do.'
This knowledge combined with a fortuitous introduction
to fuse bocks by a Bussmann salesman at OSH gave
rise to the notion that we could save a LOT of weight,
cost of ownership, installation time and panel space
with no impact on a failure tolerant system.
http://tinyurl.com/o3cjb84
Referring to the FARs we find that regulatory (and
for the most part) good design practices will
protect all but battery and engine cranking
conductors from the ravages of a hard fault
(we're talking perhaps 1000 amps here) . . .
that
Breakers
http://tinyurl.com/oypxaot
Current limiters
http://tinyurl.com/k9tmfmh
Fuses vs. breakers
http://tinyurl.com/o9joztv
http://tinyurl.com/pvmvs62
http://tinyurl.com/pw2bbgg
Bob . . . [quote][b]
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