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grounding block question

Stockmanreef

Well Known Member
should the grounding blocks be placed on the firewall near the battery ground? Or can they be placed on the sub panel? Also, should one put penetrox of Noalox on the connections to the firewall or sub panel?
 
I have my main grounding block in the cabin side of the firewall, with the stud going through to the front, where I have a short jumper to tie to the battery negative terminal. This is in addition to the main airframe ground to battery negative and provides a very low impedance path to the system ground point. I don't have "small" electrical signal grounds FF; they all come through the firewall feedthrough and tie off here. Consequently, I don't put any anit-corrosion stuff on the tabs; shouldn't hurt anything but might get messy, attract dust, etc.

i-c4gXKWZ-M.jpg
 
Signals that are vulnerable to electrical noise should have their own dedicated ground wire, not use the airframe for the ground conductor. Audio jacks, especially microphone jacks, should be electrically isolated from the airframe using insulating step-washers.
Antagonists such as strobes should be wired according to manufactures instructions. Lacking instructions, I would use a twisted pair of wires for power and ground (not use airframe for negative power conductor).
A light coat of grease can help prevent corrosion in a damp environment. Grease will not degrade the electrical connection provided that the terminals are properly crimped or torqued. The grease gets forced out, thus allowing a metal to metal, gas-tight connection.
 
should the grounding blocks be placed on the firewall near the battery ground? Or can they be placed on the sub panel? Also, should one put penetrox of Noalox on the connections to the firewall or sub panel?

The most common path is going to have a bolt passing through the ground block (forest of tabs) through the firewall and attached to the battery ground strap on the other end of the bolt in front, directly connecting the ground wires to the battery and not using the airframe as the pathway.
 
thanks. This clears things up for the ground. What gauge wire should connect the forest of wires to the battery ground?

Now I just have to figure out how the heck to attach the G3X shunt. It appears that it is connected to the master relay via a piece of copper, then, the two terminals connect to.....
 
Bill--

what is that piece of green material that lines the lightning hole in the picture? I would like to line a couple of lightning holes in the bulkheads.

thanks
 
Make sure that starter current does not go through the shunt.
What gauge wire should connect the forest of wires to the battery ground?
If that wire carries starter current, then it should be as big as the starter positive wire. Otherwise, it should be as big as the main power bus feeder.
 
This is how I did my grounding bus. The battery ground goes through this bolt and into the forest of tabs. I needed to make a new hole to accommodate the ground strap length that came in the kit.
oWO.jpg


The forest side looks like this with the big bolt just pointed out hidden behind these wires. Another smaller hole needs to be drilled to attach the other end of the forest bus. The stock grounding location is not used in my setup and a bolt is just added to fill the hole and nutplate.
oWh.jpg


There is no ground wire per se, the grounding goes through the battery braided strap.
 
chris--

thanks for the pictures. This is what I was thinking of doing and seeing it is very helpful.

I assume that the grounding strips don't have to be flush to the firewall. The reason that I ask is that I was wondering if I could use the original battery ground nut plate already on the fire wall as one of the attachment points for the grounding bar. I think that the bolts are the same size and the bolts with the grounding bar are long enough to stick out far enough out of the back of the back off the nutplate to use as a connection point. Is it a bad idea to connect something to the bolt sticking out of the back of a nutplate?

Does this make any sense? Or is it a stupid idea?
 
I would make sure the bus sits on the firewall as flush as possible to maximize the contact area between the bus and the firewall. Just my opinion, I'm sure one of the engineers here can give a good electrical explanation either pro or con.
 
Does this make any sense? Or is it a stupid idea?
Not a stupid idea. It shows ingenuity.
But I would not do it because a steel bolt is a poor electrical conductor.
Although a short steel bolt might not offer much resistance.
It will not look good.
How about replacing the nutplate with a nut and use a brass bolt?
 
I use the technique you describe for holding prop balance weights on the inside of my spinner bulkhead. But, and it's a big but, I have access to both ends of the fastener.

If you use the technique on a firewall bolt, you lose control over the torque on the bolt itself. Any tightening torque you apply to a nut on the back side of a nutplate will be loosening torque on the bolt.

If you're serious about doing it, I'd look at the cross section resistance of a copper (or more realistically, brass) bolt vs steel, as others mentioned.

Charlie
 
Ken,

I put my two Forest of Tab (FoT) ground blocks on either side of the firewall and bolted through them with brass bolts. This was done so I wouldn't have any potential (pun intended) grounding issues. After the wires were installed, they were drawn back to the side so they would not interfere with removing the battery.

What surprised me was that I need more tabs aft of the firewall and only used two tabs on the forward side.

Note, the AN bolts in these pictures were replaced with brass bolts, washers, and nuts.

Forward side -- Aft Side

(Click to enlarge)
 
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thanks. This clears things up for the ground. What gauge wire should connect the forest of wires to the battery ground?

Now I just have to figure out how the heck to attach the G3X shunt. It appears that it is connected to the master relay via a piece of copper, then, the two terminals connect to.....

Ken:

I'm assuming you're referring to the ammeter shunt. If you look at the 3rd picture on this page: https://turnerb14a.blogspot.com/2018/12/more-cowl-baffles-wiring-control-cables.html you will see the shunt between the two feeds from the alternator and standby alternator, connected to the main cable that goes through the firewall to the main power relay. Vic Syracuse recommended this setup - we drew it on the firewall (photo here: https://www.dropbox.com/s/75yrjc82ygs48nh/IMG_0187.jpg?dl=0) and I just copied that setup. As you can see I used ANL fuses for each alternator - I used short pieces of very heavy (6 ga) wire to connect each of these to the shunt. The shunt has a tiny amount of resistance and the two wires across this resistance measure current (at least that's the way I understand it).
 
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