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  #1  
Old 03-30-2021, 09:19 AM
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Default Remote Ground Block to Firewall Connection

I am putting my ground block on the aft side of the subpanel. Question is:

How large a wire to use between the ground block and the 1/4-28 bolt that the battery ground is connected to on the firewall? 8 gauge would seem large enough, but is there a way to determine based on the loads or is there a better way?
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  #2  
Old 03-30-2021, 10:46 AM
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Default here's what Bob Nuckolls says

Someone asked Bob Nuckolls a similar question a couple weeks ago.

http://forums.matronics.com/viewtopi...5815a91c8a53fa
.
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Last edited by johnbright : 03-30-2021 at 10:49 AM.
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  #3  
Old 03-30-2021, 12:48 PM
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Default

Quote:
Originally Posted by johnbright View Post
Someone asked Bob Nuckolls a similar question a couple weeks ago.

http://forums.matronics.com/viewtopi...5815a91c8a53fa
.
I saw that, but in that case the ground tab forest was connected directly to the airframe. I can do that, but still wonder if 1) it would be better to wire the forest to the engine ground with the 8ga or larger wire, or 2) make the forest of tabs part of the airframe at it's mounting point.
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  #4  
Old 03-30-2021, 01:19 PM
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Default

Quote:
Originally Posted by rockitdoc View Post
I saw that, but in that case the ground tab forest was connected directly to the airframe. I can do that, but still wonder if 1) it would be better to wire the forest to the engine ground with the 8ga or larger wire, or 2) make the forest of tabs part of the airframe at it's mounting point.
I'm the one who asked that question on the AeroElectric list.

I was hoping to hear if not grounding the forest of tabs, as you have done, and running a separate wire to the main ground location was a better option than grounding locally.
From Bob's answer, I guess with a metal airplanes, it doesn't matter but that seems to go against my understanding of ground loops.

EDIT: I overcame my fear of being flamed on the AeroElectric lis and asked a clarifying question
The question posted on the list was : So, would it better if the forest of tabs was not grounded at the sub panel and keep the connecting wire?
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Last edited by mfleming : 03-30-2021 at 01:33 PM.
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  #5  
Old 03-30-2021, 01:50 PM
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Default

Quote:
Originally Posted by mfleming View Post
I'm the one who asked that question on the AeroElectric list.

I was hoping to hear if not grounding the forest of tabs, as you have done, and running a separate wire to the main ground location was a better option than grounding locally.
From Bob's answer, I guess with a metal airplanes, it doesn't matter but that seems to go against my understanding of ground loops.

EDIT: I overcame my fear of being flamed on the AeroElectric lis and asked a clarifying question
The question posted on the list was : So, would it better if the forest of tabs was not grounded at the sub panel and keep the connecting wire?
My fear of ground loops lead me to a similar conclusion; that is, run a ground wire to the firewall. Still don't know which way would be 'best'. So, more research...
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  #6  
Old 03-30-2021, 01:55 PM
rapid_ascent rapid_ascent is offline
 
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Default

My ground block is mounted to the firewall (air frame) and my current plan is to connect directly from the battery negative terminal to the ground block with a AWG 2 equivalent braid. Some may say AWG 4 is sufficient. This essentially is what Vans has but they suggest the connection to a recess stiffener. The engine ground is connected later on to the firewall. I'm not that far yet, but I am at the point of making the battery to ground block connection.
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  #7  
Old 03-30-2021, 02:35 PM
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Default

Quote:
Originally Posted by rockitdoc View Post
My fear of ground loops lead me to a similar conclusion; that is, run a ground wire to the firewall. Still don't know which way would be 'best'. So, more research...
I did it like Bob recommended - grounded the forest to the airframe behind the panel. The engine and the battery are grounded FWF together and also to the airframe. No ground loops that I'm aware of since all the noise makers are grounded together with the potential noise listeners.

I also have a 25pin ground "bus" on the panel, which is connected to the forest of tabs. Local airframe grounds are used in a few places like lights. I just did it like Bob writes in his book and it seems to make sense, the smoke is still in the wires, and no strange noises in the headsets that I have detected yet.
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  #8  
Old 03-30-2021, 03:26 PM
PilotjohnS PilotjohnS is offline
 
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Default Ground loop misinformation

Lets clarify what a ground loop really is. First it is not bad to have two ways for electrons to get back to a ground point; that is called redundancy. What a ground loop is that is bad, is when there are many ways for the return electrons to go, and the preferred route is through critical circuits, such as audio wiring. Then multiple ground return paths could cause a problem. ( hence a ground loop). This is especially significant in non metal airplanes and things that may be struck by lightning. Ouch. So the audio wiring is especially important to have only one ground return path because the signals are so low in terms of voltage and currents, any extraneous currents will cause noise.

For this case, i think grounding the forest of tabs at the subpanel is ok. Thats what i am doing, but i am running an additional ground wire forward since my substructure is fully primed and I want a really low ground resistance to both ac and dc currents, and lightning currents.
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  #9  
Old 03-30-2021, 05:41 PM
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Thats what i decided to do, too. Ground block is grounded to subpanel and connected to battery ground with 8ga. Prolly not needed, but belt and suspenders is my motto when gravity is involved. I primed allmy interior structure as well.
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  #10  
Old 03-30-2021, 06:39 PM
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Default Ground block same as master panel panel power

I ran 6ga to my circuit breaker block, so I used the same to take the ground block back to the same bolt the battery ground is tied to, through the firewall. In reality 8ga would have been fine for both, but I was in the “more is more better” phase of the build. I got over it. .
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