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From: Dale Rogers <dale.r@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel Pump Load
Date: Mon, 24 Jan 2005 0:38:23 -0500
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Wendell,

   The principal is the same, regardless of the load we're 
talking about.  The table came from Bob Nucholls' site:

http://www.aeroelectric.com/

and the 33 feet is merely the *maximum* distance that the 
rated current can be run without exceeding the temp spec.
The point of that spec is that if your run will be more 
than the maximum length allowed for that wire size, then 
you'll need to go to the next larger wire.  In theory, a 
much shorter run could tolerate slightly higher than the 
"rated" current.  I don't recommend doing that, though.  

   To address your pump circuit, you need to know what the 
maximum current draw is for the *stalled* pump.  Most likely 
the rating given will be for that condition.  So, if your 
pump is rated for, say, 8 Amps, #18 wire will give you a 
25% fudge factor (#20 is one amp too small) as long as your 
total run - B+ AND return - doesn't exceed 11 feet.  If it 
does, then you should use #16 wire.  Protection for the 
wire should be a 10A fuse/breaker.  That assures that the 
fuse will yield before the wire overheats, and that it 
won't trip under normal operation.

Regards,
Dale R.


> From: "Wendell Voto" <jwvoto@itlnet.net>
> Date: 2005/01/23 Sun PM 07:25:18 EST
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: Fuel Pump Load
> 
> Thanks Dale,
> I was really referring to the fuel pump breaker, didn't make that clear. I
> believe Tracy said to go to the higher breaker on this service.
> I have not seen as yet any real world wire sizing tables, were did you get
> the info for the 30 feet?  This is a more practical footage for aircraft
> wiring.  I have  table from powerstream.com giving 18ga. as capable of 16
> amp for chassis wiring but 2.3 amp for transmission wiring.  Would aircraft
> fall between these or is the transmission closer to what we need?  I don't
> like calculating from resistance per K feet and such.  Quick look-up tables
> is what I'd prefer if they exist for practical vehicle/aircraft wiring.
> Make any sense?
> Wendell