flickroll

flickroll

Well Known Member
I'm in the process of wiring up my panel. I want to have really good grounds for every device at the panel. I have bought grounding blocks from Stein to ground each wire to, and I will run a wire from the grounding blocks to the battery ground in order to keep all grounds in the airplane at the same potential. Question: which size wire should the battery ground be? I was thinking about an 8 AWG. The next wire size that I have in my wire inventory is a 12 AWG. I don't see any disadvantage to the #8 except for just a little extra weight. I do not intend to ground the grounding blocks to the airframe at the panel. Thoughts?

Jim Shannon
RV-8 N52VV
Charlottesville, VA
 
Just as a general rule...size the wire according to the alternator capacity...whatever size wire you chose for the alternator output, that is the minimum size to use on the ground block. If you think you will ever AMP-UP to a larger alternator, now is the time to plan on that wire gauge selection.
 
flickroll said:
Question: which size wire should the battery ground be?

Jim Shannon
RV-8 N52VV
Charlottesville, VA
Click to expand...

As I read the first part of your post, you were only listing electrical loads in the panel.

Your question above however is a bit confusing:confused: If you looking for the size wire to take your instrument ground block back to the battery, the #8 will be way more than enough.

But if you want to just ground the battery to the airframe, and let the airframe carry all of the ground loads, then the #8 will become a short lived fusible link for the starter.

Use a heavy ground strap, or a cable at least the size of your starter feed cable to ground the battery. You can then run the #8 from that ground point back to your instrument ground block, although it is going to be redundant to the airframe carrying the same load. Many folks do add the wire, as extra insurance against electrical noise.

On a firewall mounted battery setup, I would add it. For a rear battery, probably not.

Good luck.
 
Try Aeroelectric Connection.

for the Avionics, I used his suggestion of a mated pair of 25 pin Dsub connectors with multiple wires from the connectors to the ground block. This lets you crimp a male pin on each ground wire for the electronics, and just push it in the DSUB block. See page 18-11 of this PDF:
http://www.aeroelectric.com/articles/Rev11/18Audio_R11.pdf

IMG_2515.jpg

IMG_2518.jpg


For the heavier loads I ran panel ground wires of appropriate gauge for each device (say a switch or whatever) directly to the "forest of tabs" ground block on the aft side of the firewall.
 
Sorry for the confusion. What I am trying to do is eliminate all electrical noise before it has a chance to start. So what I want to do is have a single point ground for all panel mounted devices, and this grounding system will be interconnected grounding blocks (2 ea.) with a #8 wire run back to the battery ground on the firewall. Thus by doing it this way there cannot be instrument grounds with differing potentials. The wire from the battery negative to the firewall ground (which also grounds the engine) is a #2 AWG cable. The #8 I am referring to is only a wire used to commonly ground all of the instruments.

Jim
 
Honda Style Grounding

The next plane I build I am going to wire it like a Honda, with a separate ground wire to everything.

Hans
 
flickroll said:
Sorry for the confusion. What I am trying to do is eliminate all electrical noise before it has a chance to start. So what I want to do is have a single point ground for all panel mounted devices, and this grounding system will be interconnected grounding blocks (2 ea.) with a #8 wire run back to the battery ground on the firewall. Thus by doing it this way there cannot be instrument grounds with differing potentials. The wire from the battery negative to the firewall ground (which also grounds the engine) is a #2 AWG cable. The #8 I am referring to is only a wire used to commonly ground all of the instruments.

Jim
Click to expand...

In that case, you have it right------good.

Carry on:D
 
Well - not quite....

Sorry for the confusion. What I am trying to do is eliminate all electrical noise before it has a chance to start. So what I want to do is have a single point ground for all panel mounted devices, and this grounding system will be interconnected grounding blocks (2 ea.) with a #8 wire run back to the battery ground on the firewall. Thus by doing it this way there cannot be instrument grounds with differing potentials. The wire from the battery negative to the firewall ground (which also grounds the engine) is a #2 AWG cable. The #8 I am referring to is only a wire used to commonly ground all of the instruments.

Mike S said:
In that case, you have it right------good.

Carry on:D
Click to expand...

In the system described, where is the "single point"?

Make the single point the firewall - and drop the two #8 links to the firewall. What you described is not exactly a "single point".

These #8 links will still be sharing current pulses from the equipment, and causing small voltage variations at the equipment that is dependent on other equipment. What ground reference will your voltage regulator use?

Just take all of the avionics ground lines directly to the firewall - making it a true single point. The system described probably would be OK, but why bother when the fix is so easy?
 
flickroll said:
Sorry for the confusion. What I am trying to do is eliminate all electrical noise before it has a chance to start. So what I want to do is have a single point ground for all panel mounted devices, and this grounding system will be interconnected grounding blocks (2 ea.) with a #8 wire run back to the battery ground on the firewall. Thus by doing it this way there cannot be instrument grounds with differing potentials. The wire from the battery negative to the firewall ground (which also grounds the engine) is a #2 AWG cable. The #8 I am referring to is only a wire used to commonly ground all of the instruments.

Jim
Click to expand...

O.K., time out. Confusion reigns here.

Are you mounting the above mentioned grounding blocks directly to the sub panel, or other airframe part, and running a #8 wire???

Or, are the grounding blocks electrically isolated (insulated) from the airframe, and only the #8 wire is carrying the ground load.??

If the latter, as I understood you to mean, it sure does sound like as close to a "single point" ground as you can reasonably expect with this setup.

If you are doing it as in the former, (which I think Gil is assuming) then I definitely agree with Gil about just mounting at the firewall.

The B and C kit is set up to use a single brass bolt to mount the ground tab to/through the firewall, and anchor the ground strap also.
 
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Thought so

Thanks for the reply, I had figured that is what you were doing.

As far as I can see things here, this should work fine--------electrically it is the same as mounting the tab block on the FW, and using longer individual leads from each instrument, as Gil suggested.

Either one should work just fine. Your method seems like it would be less cluttered.

Hopefully Stein, or another professional in the avionics world will chime in.
 
It is not exactly electrically the same...

Mike S said:
Thanks for the reply, I had figured that is what you were doing.

As far as I can see things here, this should work fine--------electrically it is the same as mounting the tab block on the FW, and using longer individual leads from each instrument, as Gil suggested.

Either one should work just fine. Your method seems like it would be less cluttered.

Hopefully Stein, or another professional in the avionics world will chime in.
Click to expand...

As I said earlier, where exactly is the "single" ground point?

"Electrically the same" and "RF grounding the same" are not compatible...:)

Why bother with the two blocks and the #8 wire that will be sharing ground currents?

Just take the grounds directly to the firewall - and define the firewall itself as the "single ground point" for the entire aircraft, not just the avionics.

In practise, it probably would work, but why not follow the theory and make a true single point ground? It is even likely to be less work in this case.
 
Not exactly...

flickroll said:
That is exactly what I am doing. One single ground point.

Jim
Click to expand...

Your definition is actually three grounding points connected by two lengths of #8 wire. Ground currents will be shared (and interact) in the #8 wires.

See posting above...
 
az_gila said:
Just take the grounds directly to the firewall - and define the firewall itself as the "single ground point" for the entire aircraft, not just the avionics.
Click to expand...

This is not practical on an -8, which is why I am going to use the method described.

Jim Shannon
 
flickroll said:
This is not practical on an -8, which is why I am going to use the method described.
Click to expand...

In my 6, I ran a #8 from the main firewall ground, to a junction box under the seat. Numerous grounds attach to that junction.
The loads don't exceed the amperage limit of the #8.

Although some small wing tip lights ground to the wing itself, I'm not a fan of using the airframe as the total ground.

L.Adamson --- RV6A
 
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