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Connecting two grounding blocks

claycookiemonster

claycookiemonster

Well Known Member
I intend to have a grounding block on the firewall for forward units and one on the back side of the instrument panel. I have been advised to connect these together to keep all grounds unified.

What wire gauge should be used? Both blocks will also be grounded to the airframe where they are mounted.
 
What Mike said

I used a through bolt with grounding blocks on both sides.
Works perfectly !!
 
I had originally thought I'd mount these back to back on the firewall too. I'm just seeing the distance from instrument panel to the firewall and all the other wires that need to be routed there. For the moment, two separate blocks with a connection seems cleaner than putting them together and having to lead all the grounds to one place. We'll see.
 
maybe your setup is different than mine, but I chose not to put a forrest of tabs on the hot side of the firewall and I didn't really feel like I missed anything. I don't really having any significant grounds out there other than the Pmags which I chose to ground with ring terminals to two separate points for redundancy anyway.

Did I forget something else? It's been known to happen :)
 
What size wire to use between the two ground blocks... Add up the amperage for all the devices going to the instrument panel ground and then consult the wire chart in 43.13.

Here's the chart.
 

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I highly recommend you use a BRAIDED GROUND STRAP for this application. You "should" already have a braided ground strap between your engine block and the firewall.

Ground.jpg

Each ground block should be individually grounded with the strap connecting the blocks together. The strap is there to minimize ground loops between the blocks, not for passing large amounts of current. Using a wire, even a large gauge one, can introduce AC/RF interference which can drive an avionics technician crazy something braided ground straps avoids. Don't ask how I know.

You can get braided ground straps at your local hardware, I mean aviation, store. ;)
 
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Desert Rat said:
maybe your setup is different than mine, but I chose not to put a forrest of tabs on the hot side of the firewall and I didn't really feel like I missed anything. I don't really having any significant grounds out there other than the Pmags which I chose to ground with ring terminals to two separate points for redundancy anyway.

Did I forget something else? It's been known to happen :)
Click to expand...

I agree. I never found a need for a forest of tabs on the hot side of the firewall.
 
claycookiemonster said:
I intend to have a grounding block on the firewall for forward units and one on the back side of the instrument panel. I have been advised to connect these together to keep all grounds unified.

What wire gauge should be used? Both blocks will also be grounded to the airframe where they are mounted.
Click to expand...

Also… the ground block attached on the instrument panel needs to be insulated from being grounded to the structure. Otherwise, there’s no point in connecting the two.
This bit of advice came directly to me from Mr. Bob Nuckolls himself.
 
I also forewent the forest of tabs on the hot side. A dual/redundant electrical system and dedicated grounds needed for both EI and EFI means lots of ground paths FWF. That said, adding the strip didn’t increase expected reliability. Not pretty but a component was eliminated (though not yet in the attached photo).

FWIW
 

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mfleming said:
Also… the ground block attached on the instrument panel needs to be insulated from being grounded to the structure. Otherwise, there’s no point in connecting the two.
This bit of advice came directly to me from Mr. Bob Nuckolls himself.
Click to expand...

Perhaps, but the point may be about confidence in the connection to airframe ground. Why worry about dissimilar metals and fasteners on primed aluminum maintain a good ground over the years?

I typically use the longer tab block and cut it in half. The big bolt half is on the inside of the firewall. The engine grounds on the side of the big bolt. On the cabin side of the big bolt I use a #10 wire to jump to the other half of the tab block that is now mounted on the next bulkhead aft, with the tabs facing aft. This block is used for all the avionics. On my planes the avionics take a total of 10-12 amps, so the #10 wire is overkill.

The larger loads go to the firewall tab block (pitot heat, autopilot servos, all the lights and such).

Carl
 
What about that big nut?

Freemasm

Your solution actually looks really great, but what about that big nut holding the whole thing together? I have the same nut, screwed on a little further, and wonder the same thing…why isn’t it a locknut of some kind? If it unscrews and you (me too) lose the grounds, we’re pretty much out of noise.
 
Thanks but it is not even finger tight yet. Still routing. Ex = You’ll see the battery + leads un-terminated and in space. No plans to follow and I’ve never laid out FW componentry before. Trying to minimize my mistakes and related expenses going forward. Been there. Done that. Got the tee shirt

Edit = Sorry. Reading on my phone and I missed your point. You could utilize a locking nut but a lock washer would suffice and both standard nut and lock washer can be found in brass.

Something interesting, to me at least. The ground strip I got from B&C has brass bolt washers and nut. The one I got from Stein has standard plated steel washers and nut.
 
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I rolled my own, but similar to the B&C product. I had two copper blocks that I bolted together through the firewall, sandwiching the firewall between them. That give me a common ground point on both sides of the firewall, and quite effectively connected the airframe to ground as well. I did not need any ground tabs FWF. Main battery ground was bolted directly to the block.
 
What would a guy need a forest for on the forward side of the firewall? Battery ground, and engine ground is all I have up front.
 
“Modern” EI and FI systems. Grounds for coils, injectors.

Back-up gens/alts that aren’t case ground

Second batteries.

Etc.
 
Cookie,

I did just what you’re talking about. I used an 8 ga wire to connect the three forrest of tabs. 200 hrs later and all is well.

Cold side of firewall.


Top of left gear tower.


FWF
 
Nothing connected in FWF

I must admit that despite having a forest of ground tabs in FWF, there's nothing connected to it.
On the big brass ground bolt there's only the battery cable, the engine ground strap and the two ground cables from the EFII harnesses.
 
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