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Single ground vs. distributed ground

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sat Apr 26, 2014 1:12 pm Post subject: Single ground vs. distributed ground

I'm in the process of wiring the panel and avionics on my Velocity (composite, canard).



I have built an Avionics Shelf which runs the width of the cabin just behind the panel. The shelf is made out of a pair of 1" aluminum angle stock and a sheet of aluminum on top. 



On the right side of the shelf I have mounted a ground block that connects to the battery via 2AWG welding cable. 



As I am connecting wires, the number of wires that are attaching to the ground block keeps increasing.   



I can think of a couple of solutions:



1) crimp multiple wires to a single terminal. With the 22AWG wires, I could get up to four wires in a single (red) terminal .



2) Make another ground block and mount it to the left side on the avionics shelf.  This would have the added benefit of eliminating ground wires from the bundle crossing over to the right side ground block. 



I'm leaning towards #2, but I'm wondering what the opinions are on these solutions or if there's one I haven't thought of.



Thanks in advance.

Don

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tim2542(at)sbcglobal.net
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Posted: Sat Apr 26, 2014 3:38 pm Post subject: Single ground vs. distributed ground

Buy an avionics ground bus from Bob K. Sweet and simple single point ground system for the avionics.

Just wondering....why 2awg wire to the avionics? Seems rather large.

Tim 



 	  Quote: 	
		   On Apr 26, 2014, at 2:12 PM, "donjohnston" <don(at)velocity-xl.com> wrote:

 

 

 

 I'm in the process of wiring the panel and avionics on my Velocity (composite, canard).

 

 I have built an Avionics Shelf which runs the width of the cabin just behind the panel. The shelf is made out of a pair of 1" aluminum angle stock and a sheet of aluminum on top. 

 

 On the right side of the shelf I have mounted a ground block that connects to the battery via 2AWG welding cable. 

 

 As I am connecting wires, the number of wires that are attaching to the ground block keeps increasing.  [Embarassed] 

 

 I can think of a couple of solutions:

 

 1) crimp multiple wires to a single terminal. With the 22AWG wires, I could get up to four wires in a single (red) terminal .

 

 2) Make another ground block and mount it to the left side on the avionics shelf.  This would have the added benefit of eliminating ground wires from the bundle crossing over to the right side ground block. 

 

 I'm leaning towards #2, but I'm wondering what the opinions are on these solutions or if there's one I haven't thought of.

 

 Thanks in advance.

 Don

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=422415#422415

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sat Apr 26, 2014 4:04 pm Post subject: Re: Single ground vs. distributed ground

 	  tim2542(at)sbcglobal.net wrote: 	
		  Buy an avionics ground bus from Bob K. 	




Well that would result in scrapping and undoing what I've already done. 



 	  Quote: 	
		  Just wondering....why 2awg wire to the avionics? Seems rather large. 	




Couple of reason: 1) I have more than just the avionics being grounded at that block (trim motor, AP servo, cooling fan, etc.). 2) I had the wire and the room.

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Dragoon6

Joined: 06 May 2014
Posts: 3
Location: Los Alamos, NM

Posted: Tue May 06, 2014 7:53 pm Post subject: Re: Single ground vs. distributed ground

Don, 



I have a Glasair (i.e. all fiberglass) airplane, which I bought rather than built. I am rewiring to install new equipment and I've discovered no less than 5 grounding locations. I have one (large) main ground bus, along with smaller ground buses located in various regions behind the panel: one on the floor, one on the pilot's side, one on the side of my nag/com stack, etc.  



So long as these buses are connected and that you stay away from ground loops, you should be fine with multiple grounds. My radios and such were fine before I tore everything apart. The only issue I had was loose/improperly installed coax connectors and a bum engine monitor. 



Be sure to keep your maximum voltage drop to less than 0.5V (as per the AC 43.13-2B) if you have a 14V system. I am increasing a few of my ground wires between the various smaller ground buses or terminal blocks: maybe from a #14 AWG up to a #12 or #10 AWG. 



I run a 60A alternator and use #4 AWG for my battery and starter (long runs) but a #6 AWG for my alternator line to the hot bus. My battery has two #4 AWG ground lines, one running to the main ground bus while the other runs to the engine case. 



Moderation is always a plus, but having more than one ground bus in a glass airplane is not the end of the world. Plan your layout well, as I can attest to the fact that trying to track a rat's nest of wires after the fact is NOT fun. 



Best wishes and have fun!

Travis 

Los Alamos, NM

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