Subject:
[FlyRotary] Re: CBs and fuses
Regarding
protecting
wires
instead of loads, when dealing with a $10,000
radio,
or a $7,000 EFIS I'm much more concerned with
the
load than the wire. Call me crazy.
John
I think you’ll find that the radio and EFIS have
protection built in (internal fuse, fusible link, etc); or if the radio is
causing the fuse to blow, it is toast already, or perhaps the load can tolerate
short-term current that you wouldn’t want your wire to carry when it
shorts to ground or another wire. The over heated wire starts a fire and
burns up your plane.
Whatever the reason; to quote Bob Nuckols, “Fuses
and Circuit breakers are included to in the electrical system to accomplish
only one thing: keep the wiring from creating a fire hazard in the event that
the wire becomes overloaded.” The FAA publication EA 43-13 says “Protect
the wire with the circuit breaker or fuse located as close as possible to the
electrical power source”; and “The circuit breaker or fuse should
open the circuit before the wire emits smoke” (Duh!). It also
includes the words “In order to obtain the maximum utilization of the
connected equipment . . “
Clearly the two issues are tied together, the wire sized
for “maximum utilization of the equipment” and the circuit
protection protecting the wire (and the airplane) in the event of a short.
FWIW,
Al
---
Al Gietzen <ALVentures@cox.net> wrote:
>
John;
>
>
Joe gave you good info on loads. I am using the LS1
>
coils, and I did have a
>
15A fuse blow on one set of (3) coils. It
>
apparently happened on startup (I
>
don't recall doing anything behind the panel that
>
may have caused it), and
>
apparently under the right conditions, a high draw
>
can occur when things are
>
turned on. The engine, of course, still started and
>
ran on the other set of
>
coils, but I could tell something wasn't entirely
>
cricket.
>
>
I have looked for slow-blow blade-type fuses, but
>
have not found them.
>
>
Just as a reminder, the estimated loads are useful
>
in sizing wires, but
>
circuit protection is selected to protect the wire;
>
not the load.
>
>
Al
>
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