Ron,
I'm not familiar with Navy ways (thanks for going that route, incidentally). In heavy industry we only shield one end due to potential (no pun intended) for a ground loop.
Do you know why they ground both sides? (Is the possibility for a ground loop mitigated by the short distance between grounded points and anticipated low differentials in voltage?
BTW, the tips are simply beautiful.
Thanks,
Mike
Thanks Mike.
The short version is that to create a ground loop, you need to have a difference in potentials between both ends of the circuit, which in this case would be one of end of the shielded cable versus the other. And that doesn’t exist in my installation. I’ll explain...
First off, a ship is ungrounded - every energized circuit, including shielding, has a ground or return phase that goes back to the source; this is done to prevent potential between human beings and steel decks and hull (which is a good thing in a wet environment).
Much like ships, airplanes are hulls too. So, you can have your “ship” essentially ungrounded by returning all grounds back to the source. This is commonly referred to as a two-wire system, which I use and advocate.
Incidentally, in my current career (pun intended), I build and manage power plants. We have both open (one end) and closed (both ends) grounded circuits for the various reasons we’re discussing. However, there are two different topics here, single wire vs two wire and open vs closed grounding. The thing is that you don’t have to only use one method for an airplane, especially a metal hull airframe. You can mix and match as needed by each system; it just makes it a little more complicated to ensure which systems are grounded which way and document, document, document...
I have a return ground for each load that runs back to a ground block that is a single ground point for the electrical system. Now, most airplanes don’t live in salt water (some do) and you can do a hybrid system which has some grounds to the hull, but I would limit this to only small loads that do not generate EMF. I would run my strobe lights back to ground, but having a stall warner go to hull ground would be fine.
For my circuits, significantly the wingtip lights we’re talking about, I have a ground wire contained within at least one wire bundle, and then I ground my shielding to that ground wire - not to the hull, although mathematically, you can ground both ends to the hull and have the same potential - assuming good conductivity of the airframe. The ground circuit wire ensures a common potential for the circuit, assuming a good copper wire, which has about 0.01 Ω per foot. This method eliminates the potential for a ground loop.
It’s well documented that both single wire and two wire systems work well, however the main advantage of a two wire system, which I use, is minimizing EMF, which creates the noise we hope to avoid. The downside is extra work, cost of the wire and the weight. There’s probably a primer war like forum somewhere for 2 vs 1 wire systems, but because you’ve asked, in my opinion, the effort is minimal (you’re already running one wire to the same spot), the cost is small compared to the total avionics package and the weight is also not significant on the aircraft; I calculated 5.5 pounds extra on my current RV. I want to point out that if you're building a composite or wood airframe, then your only option is a two wire system.
My evidence that my installation method is effective is that the three airplanes I’ve built were done the way I describe and are absolutely noise free. My latest RV (build #4) has a Garmin G3X system, and while running through the magnetometer test, I barely got any deflection while I stepped through the entire test. I’m hoping my latest build (likely my last) will have the same outcome.
My advice is to ground both ends to keep the noise in the circuit, and ground one end to keep the noise out of it...build on.