[rvator4twa]

My RV-6A flew about 200 hours with a Subaru and now I am replacing it with a rebuilt O360 with dual EFII systems. One of my helpers, a shade tree auto mechanic suggested that the firewall mounted negative battery terminals should go to the engine case rather than one of the firewall set of bolts holding the sea of interior tabs. I don't believe Van's instructions suggest that although they aren't perfectly clear.

 

[vlittle]

Follow the Van's plans. Ground battery to FW, then engine nearby to the same point.

Less likely to have a broken wire causing your electrical system to fail completely. Main connection is not under vibration and there are half as many.

 

[bret]

I have 5 grounds engine side.

 

[Carl Froehlich]

Use this to solve a variety of ground issues: http://www.steinair.com/product/20tab-grounding-buss/

Mount it on the firewall with the tabs on the cabin side to have a central ground for all your stuff. Either connect the battery ground to the firewall side of the ground lug (firewall mounted battery) or the aft side of the ground lug (battery mounted aft of the firewall. Run a ground wire for the engine from the lug to the ground lug on the starter. Use the same gauge wire for the engine ground as you do the starter power.

I find #2 or #4 welding wire great for starter ground and power, and for the run to the starter solenoid for aft mounted batteries. I took a torch to this stuff to see how it handled heat - it did better than aircraft Tefzel wire. Even so, I run all wires that get routed under the cylinders in a piece of fire sleeve.

I recommend avoiding using the air frame for grounds, especially avionics.

Carl

 

[sf3543]

Ground the battery to the airframe.
Also ground the engine to the airframe using a case bolt on the engine to a ground on the airframe. I always use a #2 AWG wire for this.
The motor mounts do not provide an adequate electrical path for grounding.
Poor grounding can be the result of many electrical issues.
Good luck.

 

[Canadian_JOY]

And now for the dissenting opinion... Take a look at the Grumman airplanes. They all have the battery ground connected to the engine case, then the engine case connected to the airframe via bonding straps. This works exceptionally well, and has proven robust and durable, in aircraft that are now pushing 45 years old, and often with many thousands of flight hours on them.

If you model the circuit using a resistor as each ground connection (because each ground connection IS a small resistor) it's very quick and easy to see why the primary grounding point should be the engine. After all, it's the engine case that's acting as the return path for the largest current consumer in the airplane, the starter, and it likewise is the return path for the next largest flow of electricity - the alternator. Grounding the battery directly to the engine ensures these large current flows transit the smallest number of mechanical connections (resistors).