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06-02-2016, 09:41 AM
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Join Date: Mar 2016
Location: Rockland County, NY
Posts: 195
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determining circuit breaker size
I have the Aero Electric book. I seem to reference the book depending on what area I need knowledge on. One thing that I did not see in the book so far, is how to determine the size of the circuit breaker required for a certain circuit. Can anyone give some insight on how I could determine what size breaker to use on a specific circuit? Or provide me a reference in his book on where to look.
thanks in advance
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06-02-2016, 09:58 AM
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Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,563
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The basics will be: Determine the total amount of amperage the circuit will feed, then provide for a percentage above that to allow for a margin of safety above whatever that total amperage would be. Simplistic approach that I am sure can be expounded upon by more expert advisors. They may provide more specific details (the devil is always in the details isn't it?).
One caveat in addition to the circuit breaker size is the size of wiring feeding the circuit. Whatever amperage is being drawn by the circuit must have the appropriate size wiring for that load. That is another discussion as equally important.
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06-02-2016, 10:35 AM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Your reference for wiring and circuit breaker or fuse selection is AC43.13 which is (or should be) a mandatory document for all builders of aircraft.
There are actually only two or three pages that you will use for your wiring selection, but I don't have it with me right now. You can download it, try Google.
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RV-9A complete
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06-02-2016, 11:28 AM
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Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,189
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Most things you install will provide the information needed but, as vlittle said, you can use the generic recommendations too.
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Ray
RV-7A - Slider - N495KL - First flt 27 Jan 17
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All lines by TSFlightLines (aka Hoser)
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06-02-2016, 12:15 PM
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Join Date: Jan 2006
Location: Vonore, TN
Posts: 369
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OP Drawings
If you are building a simple electrical system the Van's OP drawings will give you a place to start for CB and wire sizes. Of course, once you vary from the Van's design you're on your own.
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John Tierney
Vonore, TN
RV-7A - N777JT Flying
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06-02-2016, 01:45 PM
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Join Date: Mar 2016
Location: Rockland County, NY
Posts: 195
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Quote:
Originally Posted by John Tierney
If you are building a simple electrical system the Van's OP drawings will give you a place to start for CB and wire sizes. Of course, once you vary from the Van's design you're on your own.
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Don't tell anyone but I am not building an RV.....
How can I see the RV drawings for reference.?
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06-02-2016, 01:54 PM
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Join Date: Nov 2011
Location: Kennesaw GA
Posts: 141
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Important!
The circuit breaker is there to protect your wire from glowing red and starting a fire, not to protect your equipment. The breaker should be sized to match your wire, not your equipment. It is okay to use a big wire, a suitable breaker and not use all of the AMPs it will carry.
Determine the maximum AMPs for a given circuit, use the size wire that will carry that load, + your safety factor and then use a CB that will protect that wire.
http://www.aeroelectric.com/articles/wiresize.pdf
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Last edited by jdearborn : 06-02-2016 at 01:57 PM.
Reason: information link added
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06-02-2016, 04:41 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Update:
AC43.13 Change 1
page 11-13 for breaker/fuse sizes.
pages 11-30 and 11-31 for wire size vs load and length selection.
You choose the wire size based on load and length first, then you select the breaker size. It is acceptable to use a smaller breaker, as its only purpose is to protect the wire.
If a load needs a fuse to protect it, it is likely a non-aircraft part (or a Garmin Aera!). In this case, a separate fuse as close to the load as possible is acceptable, as specified by the manufacturer. In general, this is shoddy design and to be avoided as much as possible. All of the avionics widgets that I designed either did not require overcurrent protection or had internal fuses to prevent smoke.
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
Last edited by vlittle : 06-02-2016 at 04:43 PM.
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