psm(at)att.net
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 Posted: Mon Nov 10, 2008 3:50 pm Post subject: Fuse sizes - another point of view. |
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I decided to use fuses on my Zodiac XL. Further, I decided to use
only fuse sizes in 5 amp increments - 5, 10, 15, etc. I did this for
my convenience rather than a need to match exact current loads on each circuit.
Fuses are disaster prevention devices rather than current
regulators. A normal fuse will blow when exposed to the rated
current for a very short time. A short circuit from power to ground
will quickly draw a huge current, so a fuse of nearly any size will
protect the wiring in that circuit.
Wiring is not meant to melt at the rated current like fuses are. The
normal standard for the current limit on any size wire is that
current that will cause the temperature of the wire to increase by 10
degrees. It takes a whole lot more current than that to melt the wire.
My other decision was to put the fuses behind the instrument panel,
as is commonly done in cars, rather than some place the pilot can
fool with them in flight. This was done for a number of reasons but
two of them come to mind first. 1) In my many years of flying and
driving I have never had a fuse or circuit breaker blow. 2) In the
unusual case where a circuit does blow, I think it is unlikely that
the problem will be found while flying. This should require a major
repair on the circuit in question which can only be done on the ground.
Perhaps it is appropriate for nearly all planes to have panels full
of circuit breakers and emergency procedures that call for cycling
the circuit breaker when an electrical failure occurs. This may be a
life saver in hard IFR if the only thing that went wrong is the
circuit breaker decided to trip for some random reason. In my case -
mostly Day VFR - I figure I should focus on flying the plane rather
than trouble shooting the electronics until the flight is over.
Paul
XL getting close
(Retired Electrical Engineer)
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