Wendell Voto <jwvoto@itlnet.net> wrote:
 
> Okay,  I'm conviced, I'll go for 100% over rated current draw.


Wendell,

   You are on the verge of being a victim of over-simplification.  
I'll try to be as succinct as possible and still cover the
important considerations.

   Rule number 1: The fuse/breaker is there to protect the
wire.  If too much current is pushed through the wire, it
will melt.  You don't want that to happen.

   Rule number 2: The wire MUST be large enough to handle
all the loads connected to it - plus a "fudge" factor of
about 10 - 30%.  Remember: larger wire == more weight, so
you want to keep your wire sizes pretty close to the actual
loads they'll be carrying. Over on one of the canard lists,
someone put up a chart of how much current each wire size
will carry.  Probably Aeroelectric has a similar chart.

   Rule number 3: If your fuse is too big for the wire, the
wire will protect the fuse.  You don't want that to happen.

   Here's an example of how to pick your wire/fuse combination:

The maximum output of the alternator is 65 Amps.  A #6 wire
will carry about 54A - up to 33 feet - without an excessive
rise in temperature (35*C over ambient).  A #4 wire will
carry up to 72A under the same conditions.

Since your worst-case normal operation only passes 65A - and
is usually a lot less - a 70A breaker should never trip
unless something is seriously awry, yet still trip before
your wire gets too hot from a short.

Hope this is some help.
Dale R.
COZY MkIV #1254