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Dedicated ground

Rick RV-4

Well Known Member
I’m starting to run my wires under the seat floors and baggage area. The plans show using a local ground near the battery. Are most of you doing a dedicated ground wire up to the firewall? And if so using a #2 wire so as to match the wire going to the starter?

My plan as of now is to run a #2 wire up the right side of the aircraft to a B&C “forest of tabs”.


Thanks in advance
 
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What I did

That is what I did; #2 ground up the right side to a power bushing. Engine ground to the other side of bushing and forest of tabs inside…
 
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Ground

DC circuit ground carries the same amperage as the positive.
It would be wise to run a ground.
 
Are most of you doing a dedicated ground wire up to the firewall? And if so using a #2 wire so as to match the wire going to the starter?
Most? My guess is that it is 50:50. I grounded my battery per the plans. I have not heard of many (if any) noise issues on a 10 because of a local ground. If you do run a ground wire forward it should be the same size as the positive running forward.
 
Ours worked just fine without a dedicated ground.

Be sure to run a heavy duty ground from the engine back to the fuselage whichever way you do the rest of the grounds. Keep the starter loads where they belong.
 
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If you provide a dedicated grounding point (forest of tabs) for all sensitive electronics in the panel area, a dedicated ground wire from the battery to the dedicated grounding point is not really necessary.
The image/return current for the battery will basically follow the positive lead back to the battery in the closest conductive structure. i.e. the return current will take the path of least resistance for DC currents and mirror the positive cable as the frequencies increase, but that won't happen as the inductance of the battery cable and return will keep most RF currents localized to the forward area (forest of tabs) and local bulk capacitance.

You also don't need a dedicated return for things like large resistive loads (pitot heat, and incandescent lights).

The time when this would not apply is if you are building a composite airframe. Then you do need a dedicated electrical grounding network, and usually a dedicated electrical bonding network (for safety). This is how the big composite birds do it.
 
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I’m starting to run my wires under the seat floors and baggage area. The plans show using a local ground near the battery. Are most of you doing a dedicated ground wire up to the firewall? And if so using a #2 wire so as to match the wire going to the starter?

My plan as of now is to run a #2 wire up the right side of the aircraft to a B&C “forest of tabs”.


Thanks in advance

I grounded my batteries locally at the airframe. Noting that the only time you'll see the largest current from the battery is during engine starts, it shouldn't be a source for electromagnetic noise in flight (if you're starting your engine in flight, you won't probably won't be concerned with radio noise that point), which is really the main reason for controlling grounds. You'll be fine with a local ground for the battery, which is also per Van's OP-37 wiring drawing.

I also did as others have mentioned by bring all electrical devices, other than the battery, back to a single ground point at the firewall, that the engine is also grounded to. I too used the B&C 48 pin "forest".

A key point is to ensure your radio, strobes and other emitting or data sensitive devices are using shielded cable and/or twisted pair where appropriate.
 
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Ditto

I grounded my batteries locally at the airframe……

I also did as others have mentioned by bring all electrical devices, other than the battery, back to a single ground point at the firewall, that the engine is also grounded to. I too used the B&C 48 pin "forest".
.

Yep—this. I see no value in running a ground from the battery to the firewall. In 7 years I haven’t noticed any issues from grounding the battery locally.
 
I’m starting to run my wires under the seat floors and baggage area. The plans show using a local ground near the battery. Are most of you doing a dedicated ground wire up to the firewall? And if so using a #2 wire so as to match the wire going to the starter?

My plan as of now is to run a #2 wire up the right side of the aircraft to a B&C “forest of tabs”.


Thanks in advance

This is what I did. #2 +12V up the left side, #2 ground up the right side to the firewall and panel grounding bus. Not flying yet.

There will be a small ground bus tied to this line in the rear of the airplane for local grounds as needed as well.
 
This is what I did. #2 +12V up the left side, #2 ground up the right side to the firewall and panel grounding bus. Not flying yet.

There will be a small ground bus tied to this line in the rear of the airplane for local grounds as needed as well.

Aside from adding weight to the aircraft, this serves no purpose -- Unless you are trying to even out the mass distribution about the longitudinal axis...yeah, that's the ticket.
 
Aside from adding weight to the aircraft, this serves no purpose -- Unless you are trying to even out the mass distribution about the longitudinal axis...yeah, that's the ticket.
Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx
 
Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx

Well, there are many thousands of old 182’s flying around, battery in back, starter up front, ground return thru the airframe. My guess is that the thousands of rivets holding the pieces together and in such good contact that they are pretty much air tight form a low resistance path.
I don’t think anyone thinks the starter won’t work. The question is whether multiple paths back to the battery can lead to noise problems.
 
Ground

Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx

That's my opinion too. Even a nice solid steel auto has a huge ground cable going to the engine near or on the starter.
After 30+ years working on engines, it's the first thing I check if an engine won't turn over. What do I know? :D
 
Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx

If you are building a -10, you will be well over 100 amps for the starter inrush current…and the airframe must carry it all, just as the #2 cable connected to the starter does.

Will the airframe ground work? Sure. That doesn’t mean it is necessarily a better way…
 
Well, there are many thousands of old 182’s flying around, battery in back, starter up front, ground return thru the airframe. My guess is that the thousands of rivets holding the pieces together and in such good contact that they are pretty much air tight form a low resistance path.
I don’t think anyone thinks the starter won’t work. The question is whether multiple paths back to the battery can lead to noise problems.

The 182 is not a good example. Pretty much every Cessna out there was included in a 2006 service bulletin because of corrosion on the ground strap and attach point:
https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=16632
The repair procedure isn't encouraging to copy that principle.
 
Why not

Seems like cheap insurance to run a dedicated ground back. Will a local ground work, probably, will a dedicated ground work, for sure.
 
Opposite sides not recommended

When I was designing my electrical layout for the -10 I looked at a return earth cable. If you are going to do it run it with the +ve cable. If you run it up the opposite side of the fuselage you could end up creating electrical interference on your radios etc.
Just what I read from the Bob Nuckolls aeroelectric books.
 
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When I was designing my electrical layout for the -10 I looked at a return earth cable. If you are going to do it run it with the +ve cable. If you run it up the opposite side of the fuselage you could end up creating electrical interference on your radios etc.
Just what I read from the Bob Nuckolls aeroelectric books.

I have + up the left side and - on the right; absolutely no intereference or noise on any radio…
 
Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx

A proper connection does NOT expose the aluminum to air and therefore no oxygen available to let it oxidize. Any terminal connection to alum should get a light scuffing before the terminal is attached to remove existing oxidation. This is no different then your car, where the ground wire is attached to the steel frame or iron block; No rust (oxidation) occurring under the terminal where it is oxygen deprived.

Larry
 
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That's my opinion too. Even a nice solid steel auto has a huge ground cable going to the engine near or on the starter.
After 30+ years working on engines, it's the first thing I check if an engine won't turn over. What do I know? :D

It is very rare for a starter on a car to have a dedicated ground. Typically the negative goes to both the frame and the engine block. Most everything else is tied to those structures, including the starter. In order to make cars last longer, you will seen a ground distribution block and more ground feeds, but they just go different frame structures to keep rust from creating problems.

when dealing with large metal structures, It doesn't matter if the starter is 20" or 20' from the ground connection. If the terminal connection has high resistance, even 1" away is still the same problem as 20' away.


Larry
 
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The 182 is not a good example. Pretty much every Cessna out there was included in a 2006 service bulletin because of corrosion on the ground strap and attach point:
https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=16632
The repair procedure isn't encouraging to copy that principle.

and who is to say that 50 years down the road you will not have the same problem where your #2 cable connects to your forest of tabs? It doesn't matter where your ground cable attaches to, there is ALWAYS a risk that corrosion will form at the terminal connection.

Larry
 
Aluminum is conductive, but aluminum oxide is not. If you expose aluminum to air, oxide will form. So, in your opinion, what is the best way to make a good battery ground connection for 100 amps to the aluminum frame back at the battery that will not oxidize over time?
Tx

Our airframes are not composed of Aluminum Oxide. That would be non-optimal if they were. (see https://en.wikipedia.org/wiki/2024_aluminium_alloy)

In my "opinion" , the airframe makes for a fine ground path. Ohm's law would suggest that they are capable of carrying many many thousands of amps. Real world demonstration of lightning strikes on aircraft in flight back up this assertion.

For airframe grounding; Run the braided strap (1-2ga equivalent) from the battery [-] to the longeron. Use an AN5 bolt, lock washer - internal teeth - MS33353, AN960 washer, K1000 plate nut as the attachment stack up. Apply a thin coating of petroleum jelly (wipe it on/wipe it off) to the connection -- this serves as the gas tight barrier against oxidization.

On opinions:
For grins and giggles, measure the resistance of your airframe -- A point on the firewall to any point on the aft bulkhead. What did you get?

I measured my completed RV-7 -- it was 0.27 ohms, the in progress RV-14 was 0.3 ohms. I used exposed AN hardware, finished holes, and random points on the skin as contact points...
 
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Our airframes are not composed of Aluminum Oxide. That would be non-optimal if they were. (see https://en.wikipedia.org/wiki/2024_aluminium_alloy)

In my "opinion" , the airframe makes for a fine ground path. Ohm's law would suggest that they are capable of carrying many many thousands of amps. Real world demonstration of lightning strikes on aircraft in flight back up this assertion.

For airframe grounding; Run the braided strap (1-2ga equivalent) from the battery [-] to the longeron. Use an AN5 bolt, lock washer - internal teeth - MS33353, AN960 washer, K1000 plate nut as the attachment stack up. Apply a thin coating of petroleum jelly (wipe it on/wipe it off) to the connection -- this serves as the gas tight barrier against oxidization.

On opinions:
For grins and giggles, measure the resistance of your airframe -- A point on the firewall to any point on the aft bulkhead. What did you get?

I measured my completed RV-7 -- it was 0.27 ohms, the in progress RV-14 was 0.3 ohms. I used exposed AN hardware, finished holes, and random points on the skin as contact points...

Not sure where this is going. Nobody is questioning that the airframe is a good conductor. The question is if you use the airframe to carry the starter current, what is the best way to connect to it. I like your proposal to protect the attach point with gel or other corrosion protection just as the Cessna service bulletin suggests.

Yes, when 2024 is made, nobody adds aluminum oxide but the second it is exposed to air, the oxide will form and protect the metal's surface. If you measure resistance, you will notice that it takes poking your probe into the metal to get any reading, the surface of any aluminum that's being exposed to air is not conductive.

I won't be drilling a 5/16th hole into my tiny longeron, especially if I already know that this is a potential place of corrosion as the Cessna case shows. It could weaken the longeron quite a bit. Several smaller holes and AN3 bolts would be better.
 
If you measure resistance, you will notice that it takes poking your probe into the metal to get any reading, the surface of any aluminum that's being exposed to air is not conductive.

Uhm, nope -- it didn't take any "poking" at all, just touched the probe to the bare, ALCLAD skin.

Suggest you try as well.

Edit: On the subject of where to run the strap from the Battery [-], see page 10-23, Figure 3. Use one of the AN3-5A's that attach the battery stray to the F-1036B and F-1035 and F-1037B & F-1037C.
Edit 2: See OP 37, Page 12 Figure 1 for installation and location of the P5 strap.
 
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Uhm, nope -- it didn't take any "poking" at all, just touched the probe to the bare, ALCLAD skin.

Suggest you try as well.
The protective and non-conductive layer of aluminum oxide on the surface forms within one nanosecond and is (initially) just 4 nm thick. Maybe "poking" isn't the right term but if you saw it conducting, you did scratch off the protective layer and after you remove the probe, oxide will immediately form again.
 
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AC 43-13 gives you the recommended hardware stack-up for attaching electrical conductors to aluminum structure.
 
Oh boy, this is great! Popcorn time.
Another entry for the "never ending debates" forum. :D

Yep! I never thought this would be such an opinionated discussion but I’m loving it so far, as I’m learning quite a bit. I was leaning towards a #2 wire to the firewall (all the way from the battery) but now I’m considering just a local ground.
 
One more for you

Local ground at battery location,
as well as local ground for lights etc.
Forest of ground tabs for everything in the instrument panel.
Coms are crystal clear.
 
The protective and non-conductive layer of aluminum oxide on the surface forms within one nanosecond and is (initially) just 4 nm thick. Maybe "poking" isn't the right term but if you saw it conducting, you did scratch off the protective layer and after you remove the probe, oxide will immediately form again.

You'll need to provide the science behind the fact that the oxidized layer (not disputing it's existence) makes the AL non-conductive. Sorry, your need to press on the probe is not the science I am referring to. I have countless electrical appliance grounded to my airframe, including the battery and alternator, and they all work reliably. While many were scuffed before the terminal was installed, not all were and I certainly took more than a few nanoseconds between scuffing and installing the terminal.

By your logic, 99% of the GA fleet would have no flowing electons. Most planes use frame grounds for several or many items and most don't scuff the AL first and absolutely NONE get the terminal on within a few nanoseconds after scuffing.

For the record, I am not advocating that all use a frame ground or that it is better. Nothing wrong with dedicated grounds. Just trying to dispel these myths about frame grounding being bad.

Walt referenced the AC guidance for doing this. That is the BIBLE for aviation work. Are you telling us they got it wrong too?

Larry
 
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