NAV/Strobe/POS light fixture wiring

I’m installing Aveo NAV/STRB/POS wingtip lights on the wingtips of my RV6 build. I have the older flat top wingtips with no cutouts. Per Aveo Engineering, they recommend using a shielded harness, and it’s also a good idea to bring the ground wire back to the main ground bus. The question is - can I use the shield to also serve as the return path for ground? If not, where do I ground the shield? Both ends, or just the cockpit end?
That same question applies to any other shielded cables I will have. Which end to ground?

Following

Shield grounding mystery!

Seem to recall a saying ground one end if you wanna keep the bad signal out of the wires, both ends if you’re trying to keep the noise in inside the shield and wire.

I know on the Garmin SL 40 mike wire diagram it says to ground both ends.

Hopefully somebody knowledgeable will post an answer the question for both of us.

i wired my Rocket to accommodate either. http://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/LIGHTS.pdf

I just left it with the local frame grounding at both end (as shown), no interference noted. Some LEDs, however, use PWM current regulators that can cause interference, so using the shield as the ground return may provide better performance. In that case, I would remove the separate frame ground at the wingtip.

VV

AVEO Woes

Hello,

I went through four different iterations involving light box Gen 1,2, and 3 trying to quiet down my AVEO ZipTips.

Getting things quiet has some science and a lot of art. Most wing wiring in GA is unshielded. That said I wish I had built my wings with shielded wires. The advice I came across is to ground only one end of the shielding lest you attract a current from a ground loop. Don't intentionally pass a current in your shield, that defeats its purpose.

wawrzynskivp said:

Hello,

The advice I came across is to ground only one end of the shielding lest you attract a current from a ground loop. Don't intentionally pass a current in your shield, that defeats its purpose.

Click to expand...

This is what I don’t understand. If you are only going to ground the shield at the IP end ground bus, and also ground the light fixture at the same point, then they are electrically the same, so running the ground return through the shield shouldn’t make any difference. Would the shield not be able to drain off noise generated by the light at the same time?

Generally tie the shield at both ends. This provides the lowest impedance for attenuating noise that might be radiating from the inner conductors. As mentioned, in the case of RF noise from a switching regulator for the LEDs (common), this will help tame that.
If you use the shield as the power return, that noise will be carried on the shield and radiate, defeating the purpose of the shield. (The noise is on both the power AND power return)

The exception to tying both ends of the shield to ground is for microphone audio, or audio inputs in general. This is because the audio signals (especially microphones) are very small and it is possible that the shield might be carrying sneak currents from other equipment. If so, the noise from those currents can capacitively couple onto the audio. That is the famous “ground loop”. By only grounding one end of the shield, that situation is prevented.

Better yet is if the light designers just put a common mode filter on the LED power supply power leads. That kills most of the noise issues. Instead, they have you “fix” it with a bunch of $$ shielded cable.

So, the short answer to your question is overall shield and grounded at both ends.

Thanks Mike for the explanation. I talked to Damien at Aveo and he recommended using shielded cable, even though it isn’t always necessary with their lights. I’m not getting the fancy high dollar wingtips with installed lighting that has had some noise issues apparently. I’m just getting the small fixtures that go on the outside at the tips.
So, I’ll order 20awg 4 conductor shielded wire from Stein, and ground the shield at both ends using solder sleeves.