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Bus Bar Equivalent AWG

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Drum

Joined: 28 Jun 2020
Posts: 8
Location: Southport, CT

Posted: Thu Jul 02, 2020 4:10 am Post subject: Bus Bar Equivalent AWG

Hi - I'm putting together a ground pwr jack for my RV-8.  It's easier for me to connect two contactors using bus bar stock instead of AWG 4 wire.  Would 0.5"x.025 brass bus bar stock on a 6'' run be acceptable?  Can't find a table of brass bus bar loading data.



Thanks in advance.



Warm regards,



Drum

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_________________
Drum G
RV8 - Firewall Forward
Holly Hill, SC

art(at)zemon.name
Guest

Posted: Thu Jul 02, 2020 4:35 am Post subject: Bus Bar Equivalent AWG

Drum,

This would be a good time to think about how you are going to use your ground power jack, because that will inform how much current needs to flow through the jack, for how long, and will let you calculate the heat which would be generated. For instance, if you intend to use the jack to power the EFIS while you program it, update the database, etc, then the current is negligible. If you are going to hook up a battery maintainer, again, the current is negligible. If you are going to use it to jump start the airplane with a dead battery then you need to shove a lot of current, which warrants a fat wire or bus bar, but maybe removing the battery and charging it and then reinstalling it would be preferable. Even in this case, you have a lot of current but (hopefully) for a short time so not much heat.

Â  Â  -- Art Z.

On Thu, Jul 2, 2020 at 7:23 AM Drum <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Drum" <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)>

 

 Hi - I'm putting together a ground pwr jack for my RV-8.Â  It's easier for me to connect two contactors using bus bar stock instead of AWG 4 wire.Â  Would 0.5"x.025 brass bus bar stock on a 6' run be acceptable?Â  Can't find a table of brass bus bar loading data.

	
Â 



-- 

https://CheerfulCurmudgeon.com/If I am not for myself, who will be for me? If I am only for myself, what am I? If not now, when?

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ceengland7(at)gmail.com
Guest

Posted: Thu Jul 02, 2020 5:25 am Post subject: Bus Bar Equivalent AWG

Art makes a good point.

But directly to your question, #4 wire area isÂ 0.03268...sq in. .5 x .025= 0.0125 sq in. Brass conductivity is quite a bit worse than copper. So you'd have roughly 1/3 the area, and brass has 28% of the conductivity of copper, if the area was the same.

[url=https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials#:~:text=Brass%20is%20only%2028%25%20as,7%25%20as%20conductive%20as%20copper!&text=The%20higher%20the%20%25%20IACS%2C%20the,C%20(68%C2%B0F).]https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials#:~:text=Brass%20is%20only%2028%25%20as,7%25%20as%20conductive%20as%20copper!&text=The%20higher%20the%20%25%20IACS%2C%20the,C%20(68%C2%B0F).[/url]Â 

Offsetting that is the very short distance for a bus bar (minimal total resistance).Â 

However, a thickness of 0.065" would give you the same area, and a piece of 3/8" copper tubing (available at your local hardware store), when flattened, would give you a 0.54" x 0.095" bar.



Charlie

On Thu, Jul 2, 2020 at 7:40 AM Art Zemon <art(at)zemon.name (art(at)zemon.name)> wrote:



 	  Quote: 	
		  Drum,

This would be a good time to think about how you are going to use your ground power jack, because that will inform how much current needs to flow through the jack, for how long, and will let you calculate the heat which would be generated. For instance, if you intend to use the jack to power the EFIS while you program it, update the database, etc, then the current is negligible. If you are going to hook up a battery maintainer, again, the current is negligible. If you are going to use it to jump start the airplane with a dead battery then you need to shove a lot of current, which warrants a fat wire or bus bar, but maybe removing the battery and charging it and then reinstalling it would be preferable. Even in this case, you have a lot of current but (hopefully) for a short time so not much heat.

Â  Â  -- Art Z.

On Thu, Jul 2, 2020 at 7:23 AM Drum <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Drum" <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)>

 

 Hi - I'm putting together a ground pwr jack for my RV-8.Â  It's easier for me to connect two contactors using bus bar stock instead of AWG 4 wire.Â  Would 0.5"x.025 brass bus bar stock on a 6' run be acceptable?Â  Can't find a table of brass bus bar loading data.

	
Â 



-- 

https://CheerfulCurmudgeon.com/If I am not for myself, who will be for me? If I am only for myself, what am I? If not now, when?

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art(at)zemon.name
Guest

Posted: Thu Jul 02, 2020 6:07 am Post subject: Bus Bar Equivalent AWG

There are a couple more offsetting features of the bus bar. First, it is mounted away from everything else, so that air can circulate freely around it, helping dissipate heat. Second, it is an uninsulated piece of metal. It can get hot without damaging anything, in particular, it can get hot without melting insulation.

This is kind of a fun thought experiment but, unless you are going to crank and crank and crank your engine through that ground power jack and a set of jumper cables, I kind of doubt that the choice of a bus bar vs a #4 cable or even vs a piece of AWG 18 wire will make any practical difference.

Â  Â  -- Art Z.

On Thu, Jul 2, 2020 at 8:42 AM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:



 	  Quote: 	
		  Art makes a good point.

But directly to your question, #4 wire area isÂ 0.03268...sq in. .5 x .025= 0.0125 sq in. Brass conductivity is quite a bit worse than copper. So you'd have roughly 1/3 the area, and brass has 28% of the conductivity of copper, if the area was the same.

[url=https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials#:~:text=Brass%20is%20only%2028%25%20as,7%25%20as%20conductive%20as%20copper!&text=The%20higher%20the%20%25%20IACS%2C%20the,C%20(68%C2%B0F).]https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials#:~:text=Brass%20is%20only%2028%25%20as,7%25%20as%20conductive%20as%20copper!&text=The%20higher%20the%20%25%20IACS%2C%20the,C%20(68%C2%B0F).[/url]Â 

Offsetting that is the very short distance for a bus bar (minimal total resistance).Â 

However, a thickness of 0.065" would give you the same area, and a piece of 3/8" copper tubing (available at your local hardware store), when flattened, would give you a 0.54" x 0.095" bar.



Charlie

On Thu, Jul 2, 2020 at 7:40 AM Art Zemon <art(at)zemon.name (art(at)zemon.name)> wrote:



 	  Quote: 	
		  Drum,

This would be a good time to think about how you are going to use your ground power jack, because that will inform how much current needs to flow through the jack, for how long, and will let you calculate the heat which would be generated. For instance, if you intend to use the jack to power the EFIS while you program it, update the database, etc, then the current is negligible. If you are going to hook up a battery maintainer, again, the current is negligible. If you are going to use it to jump start the airplane with a dead battery then you need to shove a lot of current, which warrants a fat wire or bus bar, but maybe removing the battery and charging it and then reinstalling it would be preferable. Even in this case, you have a lot of current but (hopefully) for a short time so not much heat.

Â  Â  -- Art Z.

On Thu, Jul 2, 2020 at 7:23 AM Drum <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Drum" <dgrinalds(at)gmail.com (dgrinalds(at)gmail.com)>

 

 Hi - I'm putting together a ground pwr jack for my RV-8.Â  It's easier for me to connect two contactors using bus bar stock instead of AWG 4 wire.Â  Would 0.5"x.025 brass bus bar stock on a 6' run be acceptable?Â  Can't find a table of brass bus bar loading data.

	
Â 



-- 

https://CheerfulCurmudgeon.com/If I am not for myself, who will be for me? If I am only for myself, what am I? If not now, when?



 	


 	


-- 

https://CheerfulCurmudgeon.com/If I am not for myself, who will be for me? If I am only for myself, what am I? If not now, when?

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jul 02, 2020 6:39 am Post subject: Bus Bar Equivalent AWG

 	  Quote: 	
		  However, a thickness of 0.065" would give you the same area, and a piece of 3/8" copper tubing (available at your local hardware store), when flattened, would give you a 0.54" x 0.095" bar.

 	


   Art and Charlie make excellent points. Another

   possibility is to fabricate a 4AWG welding

   cable jumper that's a 'bit too long' so that

   it simply makes a graceful curve between the

   studs.



   The copper tube idea has been floated and

   incorporated in projects here on the list

   for decades. Copper is the bus bar material

   of choice and you only need to flatten the ends

   to facilitate joining at the studs. This

   technique calls for attention to keeping

   the two flats planar to each other.



   My personal choice would be the welding

   cable jumper. Easy to build, soft and

   easy to work with. Does not conduct

   mechanical forces between the studs.



   I'm recalling an invitation I received from

   an RV builder in Wichita to visit his project

   in process on local airport. We had some

   good discussion about various chapters of

   his planning. While looking over stuff fire-wall-

   forward, I noticed that he had grounded battery(-)

   to the fire-wall sheet with a little chunk of aluminum

   angle.



   I brought this to his attention and suggested

   that the thin stainless was a poor conductor

   and that forcing it to carry battery recharge

   and starter cranking currents offer potential

   for serious ground-loop effects. But more important,

   the battery mass was getting tied to airframe

   by non-structural battery terminal by way

   of a non-ferrous hunk of metal that was almost

   guaranteed to be his first electrical system

   failure.



   I think he was rather fond of his short-n-

   simple grounding idea . . . he got a bit incensed

   but it was about time for me to depart anyhow.

   Never did hear any follow-up on the project.

   But it's an experience that reminds me to

   ponder system rigidity between significant

   chunks of hardware when making hard connection

   to studs designed for terminating relatively

   soft wires.



 

   Bob . . .

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ceengland7(at)gmail.com
Guest

Posted: Thu Jul 02, 2020 7:12 am Post subject: Bus Bar Equivalent AWG

On 7/2/2020 9:37 AM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                 	  Quote: 	
		  However,           a           thickness of 0.065" would give you the same area, and a piece           of           3/8" copper tubing (available at your local hardware store),           when           flattened, would give you a 0.54" x 0.095" bar.

         	
       

           Art and Charlie make excellent points. Another

           possibility is to fabricate a 4AWG welding

           cable jumper that's a 'bit too long' so that

           it simply makes a graceful curve between the

           studs.

         

           The copper tube idea has been floated and

           incorporated in projects here on the list

           for decades. Copper is the bus bar material

           of choice and you only need to flatten the ends

           to facilitate joining at the studs. This

           technique calls for attention to keeping

           the two flats planar to each other.

         

           My personal choice would be the welding

           cable jumper. Easy to build, soft and

           easy to work with. Does not conduct

           mechanical forces between the studs.

         

         I'm recalling an invitation I received from

         an RV builder in Wichita to visit his project

         in process on local airport. We had some

         good discussion about various chapters of

         his planning. While looking over stuff fire-wall-

         forward, I noticed that he had grounded battery(-)

         to the fire-wall sheet with a little chunk of aluminum

         angle.

       

         I brought this to his attention and suggested

         that the thin stainless was a poor conductor

         and that forcing it to carry battery recharge

         and starter cranking currents offer potential

         for serious ground-loop effects. But more important,

         the battery mass was getting tied to airframe

         by non-structural battery terminal by way

         of a non-ferrous hunk of metal that was almost

         guaranteed to be his first electrical system

         failure.

       

         I think he was rather fond of his short-n-

         simple grounding idea . . . he got a bit incensed

         but it was about time for me to depart anyhow.

         Never did hear any follow-up on the project.

         But it's an experience that reminds me to

         ponder system rigidity between significant

         chunks of hardware when making hard connection

         to studs designed for terminating relatively

         soft wires.

       

                

             Bob . . .                     	
     I do try to put some variation of an 'S' curve in the flattened     copper tubing, when I use that trick. Helps relieve flex stress in     one direction, anyway...

     

     Charlie

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

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Drum

Joined: 28 Jun 2020
Posts: 8
Location: Southport, CT

Posted: Sun Jul 05, 2020 7:42 am Post subject: Re: Bus Bar Equivalent AWG

Thank you for your help.  I will look for the welding cable jumper.  My installation is aft.  Turns out on the RV8, the battery tray has 4 nut plate attachment points for the contractors to sit.  Forward, those would be the battery master and starter contactors but aft I am planning on using the locations for the battery master and ground power contactors.



Of course, since the two contactors are connected to the same rigid surface, there might not be so many large movements relative to one another, but there is enough movement to eventually create issues.  



My two objectives here are to make sure there is not interference between wiring of battery and ground power and the elevator bellcrank/pitch servo which are located just aft of the battery in the RV8. Secondly, want to make it straightforward to disconnect the wiring from the battery to allow removal of the aft baggage floor permitting access to this area.



I will send pictures when I get the opportunity.



Thanks,



Drum

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_________________
Drum G
RV8 - Firewall Forward
Holly Hill, SC

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 05, 2020 9:22 am Post subject: Bus Bar Equivalent AWG

At 10:42 AM 7/5/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Drum" <dgrinalds(at)gmail.com>



 Thank you for your help.  I will look for the welding cable jumper.  My installation is aft.  Turns out on the RV8, the battery tray has 4 nut plate attachment points for the contractors to sit.  Forward, those would be the battery master and starter contactors but aft I am planning on using the locations for the battery master and ground power contactors.



 Of course, since the two contactors are connected to the same rigid surface, there might not be so many large movements relative to one another, but there is enough movement to eventually create issues.  



 My two objectives here are to make sure there is not interference between wiring of battery and ground power and the elevator bellcrank/pitch servo which are located just aft of the battery in the RV8. Secondly, want to make it straightforward to disconnect the wiring from the battery to allow removal of the aft baggage floor permitting access to this area.



 I will send pictures when I get the opportunity. 	


   great! thanks.



 

 

   Bob . . .

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