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1. 08:42 AM - Re: Pilot accessible B lead CB (Robert L. Nuckolls, III)
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| Subject: | Re: Pilot accessible B lead CB |
At 12:50 PM 10/23/2023, you wrote:
>Thanks Bob.
>
>I can believe AFS policy of Quick Panels having a B lead CB by
>default is as much legal CYA as technical. In their defense they
>cannot control electrical power system implementation or changes on
>OBAM aircraft.
To be sure, throughout history of
electrical systems in aviation, there
are probably more airplanes with a
panel mounted breaker to the generator/
alternator feed than airplanes without.
There were a couple hundred thousand
airplanes built with breakers like those
pictured in the attachment. Non-pullable.
The 'policy' was to provide mandated
branch circuit protection from severe
overload . . . being able to pull a breaker
to mitigate a runaway alternator condition
was never a design goal.
The voltage ratings on breakers, relays
and switches are based on the ability of
the device to OPEN a circuit when experiencing
a specified fault current. A device rated
(and qualified) at 30 volts DC would
probably be in deep doo-doo attempting to
break a runaway alternator's b-lead.
In many instances policy has more to do
with tradition than with carefully considered
failure analysis or design rules for
accessories. In spite of the fact that
avionics master switches haven't been
a real thing for over 50 years, they're
still a feature on a lot of modern
airplanes.
The voltage ratings on breakers, relays
and switches are based on the ability of
the device to OPEN a circuit when experiencing
a specified fault current. A device rated
(and qualified) at 30 volts DC would
probably be in deep doo-doo attempting to
break a runaway alternator's b-lead.
Bob . . .
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