To: lancair.list@olsusa.com
Date: Sun, 5 Dec 1999 09:45:46 -0800
Subject: Fuses
Message-ID: <19991205.094548.-279357.0.refroelich@juno.com>
From: Robert E Froelich <refroelich@juno.com>
Mime-Version: 1.0

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The purpose of a fuse or circuit breaker is to protect the wiring and
load from over heating, burning and causing a fire.
Two of the arguments in favor of fuses in an aircraft are:  1) Many
circuits are not critical to a safe flight and should not be re-energized
in flight.Should an overload in the circuit cause the fuse to blow, do
you really want to send more current through the circuit and risk further
damage or fire?
2) The cost of a fuse holder and fuse is about $1.50 versus $25.00 for a
circuit breaker.The difference adds up in 30 circuits. 
A few critical circuits, such as the electric hydraulic pump to lower the
gear, need a circuit breaker that can be re-energized should it blow. 
The hope being that a transient problem caused the breaker to trip rather
than a permanent short circuit. Even these circuits,as a rule, should
not be re-energized more than once in flight.
A drawback to using fuses has been in not knowing whether a fuse had
blown.  This problem is solved with a series of red/green LED's on a
printed circuit board along with several components.  The circuit board
with it components and push button switch can be mounted in the access
door on the side panel to the fuses.  One push-on switch illuminates the
lights for a quick check of the fuses.  If all are green, all fuses are
good.  A red LED indicates that its associated fuse has 
blown. 
the diagram was published in the Australian Electronics magazines several
years ago. 
I am unable to copy the visio drawing to this E-mail.  If interested in
the diargram, send a self addressed stamped envelope to R.E.Froelich, 780
16th Avenue, Salt Lake City, UT 84103-3705.
Bob

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