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8awg line to forrest of tabs

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Dennis Jones

Joined: 17 Sep 2006
Posts: 45
Location: Poplar Grove, IL

Posted: Sun Jan 28, 2007 11:16 pm Post subject: 8awg line to forrest of tabs

Bob



My aircraft has a tandem seating configuration. I want to have the forrest of tabs toward the back of the aircraft, the location of all the electric stuff. I would rather run the #2 from the battery to the firewall pass through bolt with out breaking the line to attach to the forrest of tab bolt. Can I run a #8 from the negative post of the battery directly to the forrest of tabs and run the #2 to the firewall without a break in the line? Also what options are there to attach the #8 to the same lug as the #2?



Thanks

Jonsey

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nuckollsr(at)cox.net
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Posted: Mon Jan 29, 2007 5:26 am Post subject: 8awg line to forrest of tabs

At 11:16 PM 1/28/2007 -0800, you wrote:

 	  Quote: 	
		  

<djones(at)northboone.net>



Bob



My aircraft has a tandem seating configuration. I want to have the forrest 

of tabs toward the back of the aircraft, the location of all the electric 

stuff. I would rather run the #2 from the battery to the firewall pass 

through bolt with out breaking the line to attach to the forrest of tab 

bolt. Can I run a #8 from the negative post of the battery directly to the 

forrest of tabs and run the #2 to the firewall without a break in the 

line? Also what options are there to attach the #8 to the same lug as the #2?



Thanks

Jonsey


	


  I'm having trouble visualizing your description.

  What kind of airplane are we talking about? Do

  I understand that you want separate locations for

  the firewall pass-thru bolt and the forest-of-tabs?



  Hmmmm . . . I think I'm getting it. Is this a metal

  airplane with a rear mounted battery, midships ground

  block and a ground stud on the firewall?



  Bob . . .

        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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Dennis Jones

Joined: 17 Sep 2006
Posts: 45
Location: Poplar Grove, IL

Posted: Mon Jan 29, 2007 9:07 am Post subject: 8awg line to forrest of tabs

Yes to both questions. Steel tube and rag. 



--

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nuckollsr(at)cox.net
Guest

Posted: Mon Jan 29, 2007 11:41 am Post subject: 8awg line to forrest of tabs

At 10:34 AM 1/29/2007 -0600, you wrote:

 	  Quote: 	
		  

<djones(at)northboone.net>



Yes to both questions. Steel tube and rag.


	


   Hmmmm . . . Okay. If it were my airplane I'd "float"

   the forest-of-tabs from the airframe at whatever location

   you choose to mount it. Bring 2AWG to the ground block

   from the battery. Bring a second 2AWG from ground block

   to a thru-bolt at the firewall where the crankcase jumper

   picks up a ground for the crankcase.



   This is to accommodate systems that might have grounded

   transducers at the crankcase but get their power grounds

   at the forest of tabs. Can you elaborate why you're not

   interested in putting the tabs on the firewall? I'm still

   thinking this is electrically better even if it means some

   ground wires are a bit longer.



   Bob . . .

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue Jan 30, 2007 7:56 am Post subject: Re: 8awg line to forrest of tabs

Discussions with some customers resulted in the following tales:



1) Battery in the tail of a metal-skinned aircraft. Battery positive is to contactor and fatwire going forward. Battery negative is to the airframe. Aircraft structure is riveted double epoxy coated aluminum sheets. Big engine. 200A ground current. Scares me Bubela. Are the rivets getting hot?



2) Purchased aircraft had ground to metal airframe. New owner installed separate ground wires, one to ground everything in the left and right wings, one to the tail loads, one to the panel. Now he has amazing instrument deflections when various loads are energized. 



These tales are illustrations that ground currents are just like any other currents. I mention this because familiarity with automobile electrics where the steel chassis carries the ground currents often lead builders to ignore this essential point. 



Furthermore grounds are often grouped together or wired to "common" ground busses without much regard to the voltage drops caused by large ground currents flowing through them. Often many loads will attach their  ground connections to a smaller ground bus, often buried in the  panel right under sensitive instruments. This needs rethinking. You wouldn't put a positive high-current conductor there...!?



I agree with the "forest of tabs" approach and I suggest that the idea of other "ground busses" etc. needs some careful thinking to take grouped ground currents into consideration. 



"Never be afraid to tell the world who you are." 

  - Anonymous

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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