A lot of discussion on this, but perhaps not enough on specific steps and issues to consider on engine grounding.
My thoughts:
- Establish a common ground point on the firewall. ACS and Stein have nice ?Forest of Tabs? do to this. I like this one but I cut it in half, mounting the part with the bolt on the cabin side of the firewall. The other half (if I use it at all) gets mounted on the bulkhead behind the panel to add ?convenience? ground tabs. It connects to the same big brass ground post with a #10 wire.
https://www.steinair.com/product/40tab-grounding-buss/
Everything in the plane gets grounded here - no airframe grounds.
- Your battery(s) are grounded on this same post.
- On the firewall side I run a #2 welding wire to the ground lug on the stater. For you snorkel builders this is not convenient so the alternative is use the mounding bolt on the alternator to alternator bracket. The logic is the starter is what draws the current, not the engine - this minimizes voltage drop across the various engine joints as compared to just running a ground strap under some greasy engine cast bolt.
- Be very careful of building in other engine ground paths (like instrumentation, mag switches and such). In other words verify that if your engine ground failed (or you forgot to put it back on after maintenance) that your starter would not find some other path back to the battery ground. I hear horror stories of such incidents frying wires and panels.
- One engine ground only.
- I too am not a fan of the RV-14 engine mount ground arrangement.
Side note - I use welding wire for all battery, alternator and engine ground runs as I find it superior to branded straps (for grounds), more flexible and durable for all the other connections (as compared to standard aircraft large gauge wire). I do not use brass or copper buss bar for anything other than the ground Forest of Tabs. Specifically:
- #4 from each battery positive terminal to its master solenoid. Output of the combined solenoids gets a #2 to the starter solenoid and then from there to the starter.
- #4 for each battery ground
- #6 for the alternator output
Carl