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wire size

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Scot

Joined: 20 Jul 2009
Posts: 8

Posted: Wed Dec 05, 2012 10:03 am Post subject: wire size

I am in the process of designing the electrical system for the my RV-7.  I know this will be a very basic question, but herding electrons is not one of my strong suits.  I am starting to run wires through the wing for all the various electronics and I want to make sure I am reading the wire size figure in Chapter 11 in AC 43-13.  Just for my education lets use Duckworth Landing Lights as example.  I believe they recommend 16 AWG(for 55W lights) with a local / airframe ground.  Wanting to understand how all this stuff works I reference Figure 11-2 in AC 43-13.

   

 First, I figure the AMPS drawn per light is 55 / 14 or 3.93; call it 4 AMPs continuous.  The wire run to the lights is estimated to be 18 feet. I am including the length of the wing + a portion of the fuselage and an estimate of the turns etc to reach the panel. Depending on how fine your pencil is, the chart seems to indicate I could use AWG 18.  If I want to run the ground all the way back to the panel, then the length will be 36 feet.  Then I need to use AWG 14 with the ensuing increase is weight.  I know the weight increase is minimal for one device.  But landing lights, nav lights, strobes, etc it all adds up.

   

 Just in case someone wonders, my concern with local ground is the potential of leakage into the avionics.

  

 I am reading all this correctly.  Thank you all for your kind advice.

  

 Scott

  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 05, 2012 10:58 am Post subject: wire size

 	  Quote: 	
		  I know the weight increase is minimal for one device.  But landing 

lights, nav lights, strobes, etc it all adds up.



Just in case someone wonders, my concern with local ground is the 

potential of leakage into the avionics.



I am reading all this correctly.  Thank you all for your kind advice.


	


    Have you read the chapters on wiring and

    grounding in the AeroElectric Connection?



    The rule of thumb for voltage drop limiting

    is 5% of system voltage or 0.7 volts. A 4

    amp load produces this size of drop with

    a loop resistance of 175 milliohms. An 18'

    run of wire would have to be run with

    material having a resistance of about 175/18

    or 10 milliohms per foot. 20AWG meets the requirement

    for a single run of wire and local ground. This

    exercise is described in a paper at:



http://tinyurl.com/ar6k3ed



    Local grounds are fine as long as you perform

    due diligence for eliminating airframe ground

    loops in for potential victims by means of centralized

    ground bussing as described in chapter on grounding

    and figure Z15 in the wiring diagrams.

   Bob . . .

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Scot

Joined: 20 Jul 2009
Posts: 8

Posted: Wed Dec 05, 2012 12:36 pm Post subject: wire size

The rule of thumb for voltage drop limiting

    is 5% of system voltage or 0.7 volts. A 4

    amp load produces this size of drop with

    a loop resistance of 175 milliohms. An 18'

    run of wire would have to be run with

     material having a resistance of about 175/18

    or 10 milliohms per foot. 20AWG meets the requirement

    for a single run of wire and local ground. This

    exercise is described in a paper at:



http://tinyurl.com/ar6k3ed

 

 After reading (and re-reading) the link you sent I have calculated that using an 18 AWG wire will meet the requirement.  Using the constant of 700, 6.39 mOhm and 4 Amp draw I get a length of 27.39 feet.  If I want to I can step to a 16 AWG  and the acceptable length is 43.64.  All of this assuming a local ground.

   

 I will go back and re-read that chapter in your book.  Thank you.

  

 Scott

  

 



 

  [quote] I am in the process of designing the electrical system for the my RV-7.  I know this will be a very basic question, but herding electrons is not one of my strong suits.  I am starting to run wires through the wing for all the various electronics and I want to make sure I am reading the wire size figure in Chapter 11 in AC 43-13.  Just for my education lets use Duckworth Landing Lights as example.  I believe they recommend 16 AWG(for 55W lights) with a local / airframe ground.  Wanting to understand how all this stuff works I reference Figure 11-2 in AC 43-13.

   

 First, I figure the AMPS drawn per light is 55 / 14 or 3.93; call it 4 AMPs continuous.  The wire run to the lights is estimated to be 18 feet. I am including the length of the wing + a portion of the fuselage and an estimate of the turns etc to reach the panel. Depending on how fine your pencil is, the chart seems to indicate I could use AWG 18.  If I want to run the ground all the way back to the panel, then the length will be 36 feet.  Then I need to use AWG 14 with the ensuing increase is weight.  I know the weight increase is minimal for one device.  But landing lights, nav lights, strobes, etc it all adds up.

   

 Just in case someone wonders, my concern with local ground is the potential of leakage into the avionics.

  

 I am reading all this correctly.  Thank you all for your kind advice.

  

 Scott

[b]

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bicyclop(at)pacbell.net
Guest

Posted: Wed Dec 05, 2012 7:17 pm Post subject: wire size

Scott,

     

     If you are going to do HID, 55w will be plenty enough. If you are     going to use halogen lights, plan for more than 55w. I had a pair of     75w for years and when I went to 100w, I finally felt it was about     bright enough. I normally wig-wag them and everybody sees that     coming. I turn them both on steady for night landings. The weight     difference for larger gauge wire is negligible. Local ground will     work fine.

     

     Pax,

     

     Ed Holyoke

     

     

     

     On 12/5/2012 12:35 PM, Scott Ahrens wrote:     [quote]       The rule of thumb for voltage drop limiting

             is 5% of system voltage or 0.7 volts. A 4

             amp load produces this size of drop with

             a loop resistance of 175 milliohms. An 18'

             run of wire would have to be run with

             material having a resistance of about 175/18

             or 10 milliohms per foot. 20AWG meets the requirement

             for a single run of wire and local ground. This

             exercise is described in a paper at:

         

         http://tinyurl.com/ar6k3ed

       

       After reading (and re-reading) the link you sent I have         calculated that using an 18 AWG wire will meet the requirement.          Using the constant of 700, 6.39 mOhm and 4 Amp draw I get a         length of 27.39 feet.  If I want to I can step to a 16 AWG  and         the acceptable length is 43.64.  All of this assuming a local         ground.

        

       I will go back and re-read that chapter in your book.  Thank         you.

        

       Scott

        

       

         

          

                 	  Quote: 	
		             I am in the process of designing the electrical system             for the my RV-7.  I know this will be a very basic question,             but herding electrons is not one of my strong suits.  I am             starting to run wires through the wing for all the various             electronics and I want to make sure I am reading the wire             size figure in Chapter 11 in AC 43-13.  Just for my             education lets use Duckworth Landing Lights as example.  I             believe they recommend 16 AWG(for 55W lights) with a local /             airframe ground.  Wanting to understand how all this stuff             works I reference Figure 11-2 in AC 43-13.

            

           First, I figure the AMPS drawn per light is 55 / 14 or             3.93; call it 4 AMPs continuous.  The wire run to the lights             is estimated to be 18 feet. I am including the length of the             wing + a portion of the fuselage and an estimate of the             turns etc to reach the panel. Depending on how fine your             pencil is, the chart seems to indicate I could use AWG 18.              If I want to run the ground all the way back to the panel,             then the length will be 36 feet.  Then I need to use AWG 14             with the ensuing increase is weight.  I know the weight             increase is minimal for one device.  But landing lights, nav             lights, strobes, etc it all adds up.

            

           Just in case someone wonders, my concern with local             ground is the potential of leakage into the avionics.

            

           I am reading all this correctly.  Thank you all for your             kind advice.

                           

               Scott

             

	
     [b]

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