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http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2011.pdf

Dale R.


>
> From: "Marc Wiese" <cardmarc@charter.net>
> Date: 2005/01/23 Sun PM 07:06:54 EST
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Wire/fuse sizes in aircraft
>
> You guys really need to get the FAA's AC 43.13 1A and B (latest ones are
> greatly revised!). It is the bible for aircraft repair; and in it in the
> electrical section it gives wire sizes depending on load, voltage and
> length, and from that you can figure the fusing you need. It is required
> reading for anybody who wants to get a repairman's certificate or has
> gotten an A/P license. If your intend to build an aircraft, you need
> these books. Also check those switches-don't use AC switches. Use
> switches rated for DC.  Test will be at 8 am tomorrow.
> Marc Wiese
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
> Behalf Of Dale Rogers
> Sent: Saturday, January 22, 2005 9:06 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Fuel Pump Load
>
> 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
>
>
>
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