Grounding Blick forest of tabs

[laz]

I know this has been beat to death, but I need some help understanding this grounding issue.. I am wiring my RV8 and what I plan to do so far, is this.

1. I have a ground from my firewall battery connected to the firewall with a 5/16 brass bolt. I have a grounding strap from the engine to that same bolt.

From there I have a #6 cable going to a forest of Tabs mounted on the bulkhead behind the Instrument panel. The forest of tabs is insulated from the bulkhead so its only connection to ground is the # 6 wire ate the firewall listed above.

2. I plan to ground everything , all avionics, Efis, Lights, Fuel pumps Flap motor, virtually everything to that forest of Tabs.

Does this make sense? Will it cause a "ground loop" because my avionics share a common ground with everything else?

I have tried to get a clear answer on the Aeo electric forum but never seem to get a clear yes and no answer.

Thanks

[bret]

That's where mine is except I have two # 8 wires on two copper studs out of a solenoid going to the forest for redundancy.

[RV7Guy]

You are fine with this set up. You can locally ground your wing tip lights at the tip rib as well. I used a different set up for the grounding on the new one to save space. I'll have a bolt through the firewall as well that ties everything together. Please note, I'm not done with this set up. I'll be changing the bolts to allow for more thread clearance and the large bolt will have a self locking nut on it.


[IMG][/IMG]

Originally Posted by laz

I know this has been beat to death, but I need some help understanding this grounding issue.. I am wiring my RV8 and what I plan to do so far, is this.

1. I have a ground from my firewall battery connected to the firewall with a 5/16 brass bolt. I have a grounding strap from the engine to that same bolt.

From there I have a #6 cable going to a forest of Tabs mounted on the bulkhead behind the Instrument panel. The forest of tabs is insulated from the bulkhead so its only connection to ground is the # 6 wire ate the firewall listed above.

2. I plan to ground everything , all avionics, Efis, Lights, Fuel pumps Flap motor, virtually everything to that forest of Tabs.

Does this make sense? Will it cause a "ground loop" because my avionics share a common ground with everything else?

I have tried to get a clear answer on the Aeo electric forum but never seem to get a clear yes and no answer.

Thanks

[Raymo]

Originally Posted by laz

I know this has been beat to death, but I need some help understanding this grounding issue.. I am wiring my RV8 and what I plan to do so far, is this.

1. I have a ground from my firewall battery connected to the firewall with a 5/16 brass bolt. I have a grounding strap from the engine to that same bolt.

From there I have a #6 cable going to a forest of Tabs mounted on the bulkhead behind the Instrument panel. The forest of tabs is insulated from the bulkhead so its only connection to ground is the # 6 wire ate the firewall listed above.

2. I plan to ground everything , all avionics, Efis, Lights, Fuel pumps Flap motor, virtually everything to that forest of Tabs.

Does this make sense? Will it cause a "ground loop" because my avionics share a common ground with everything else?

I have tried to get a clear answer on the Aeo electric forum but never seem to get a clear yes and no answer.

Thanks

I am not an expert but this is my understanding.

A ground loop occurs when two electrical devices are connected (e.g. serial) but are grounded to two separate locations (e.g. wing skin and battery terminal). The two grounds will have different potentials, or resistance, causing the balance or difference of the two to run over the serial connection, causing static or interference with the signal.

Grounding all electrical devices to one common location should eliminate the possibility of a ground loop.

[deene]

Good practice in small aircraft (certified and EAB) is to have a well designed
ground system and to minimize common mode noise in sensitive subsystems.

A local common ground point (forest of tabs is a nice solution) is required for
equipment that has low level signals like avionics. The forest will need a good
connection to the battery.

For high current noisy equipment (pumps, motors, lights, etc.), the best
ground point for each (in al airframes) is the airframe itself and NOT the forest.
This equipment is very tolerant to common mode ground noise and the al
airframe is a very good path to the battery.

This approach offers good performance with minimum common mode noise in
sensitive equipment and is lighter and lower cost.

This is the Bob Nuckolls philosophy I recommend as a retired electrical engineer (computer
equipment, CPU chip design) with several graduate degrees and a good number of EAB
projects/instrument panels under my belt.

Back to the OP, I would recommend the following mods:

- Make sure the battery ground cable is also well connected to the airframe (and not just to the SS firewall)
- Remove all grounds from the forest except the avionics, and instrumentation grounds.
Also, make sure these do not have grounds to the airframe at any other point
except at antennas. Pay particular attention to the audio system
- Locally ground the boost pump, flap motor system, lights and similar equipment to the airframe

[laz]

Thanks Deen and others who responded.

It appears that I will go with the "Local Ground" for all the noisy stuff. and use the forest of tabs on the bulkhead behind the Panel for all others. This confusion all started out when I read and read and read The Aero Electric book. In the chapter on grounding there was a change that I did not really pick up on that separated the Panel grounding from the forest of tabs.

I am installing a Garmin G3X Touch with a GRT MiniX as a backup,a Garmin 650, Mode S transponder, Garmin autopilot and a second com. Stein did the wing diagram for me and just that stuff has over 20 grounds.

I did go thru some structure as well as the SS firewall. I will run large cable # 8 or #6 to the forest of tabs on the bulkhead behind the instrument panel. I Isolated the Tabs form that bulkhead because there is not much structure on that bulkhead so I figured connecting it to the firewall ground point would be best.

Thanks agin for the help.

[deene]

I'm just finishing up helping a friend install a Steinair G3X system in his RV8,
they do really nice work. I'll try to post some pics next week.

BTW, you can combine 2 or 3 ground wires into a single blue faston terminal to
reduce the number of tabs required...in fact Stein did that on our panel reducing
tabs used to 5.

Good luck, Laz, I'm sure your installation will work out fine. And good show for
seeking advice...VAF is a good deep source for help in all areas of EAB
construction.

[bjustus]

I like the idea of grounding heavy load items and "far away" non sensitive components to the airframe. I already did my landing/taxi lights this way and was planning to ground the Dynon Pitot heat locally but then saw this in the instructions:

"Do not connect the Black (Ground) wire to the airframe as a Ground connection.
Doing so will introduce high currents (10A) into the airframe. This can introduce a significant voltage drop, and potentially cause engine instrumentation, avionics,
and audio system electrical problems."

What's the best way to deal with this ground to keep from introducing noise from this high amp device? I'm assuming not a good idea to plant this one in the "forest"?